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1

Potentiometric titration and equivalent weight of humic acid  

USGS Publications Warehouse

The "acid nature" of humic acid has been controversial for many years. Some investigators claim that humic acid is a true weak acid, while others feel that its behaviour during potentiometric titration can be accounted for by colloidal adsorption of hydrogen ions. The acid character of humic acid has been reinvestigated using newly-derived relationships for the titration of weak acids with strong base. Re-interpreting the potentiometric titration data published by Thiele and Kettner in 1953, it was found that Merck humic acid behaves as a weak polyelectrolytic acid having an equivalent weight of 150, a pKa of 6.8 to 7.0, and a titration exponent of about 4.8. Interdretation of similar data pertaining to the titration of phenol-formaldehyde and pyrogallol-formaldehyde resins, considered to be analogs for humic acid by Thiele and Kettner, leads to the conclusion that it is not possible to differentiate between adsorption and acid-base reaction for these substances. ?? 1960.

Pommer, A.M.; Breger, I.A.

1960-01-01

2

Derivative analysis of potentiometric titration data to obtain protonation constants  

SciTech Connect

A methodology is described to calibrate glass electrodes and to analyze potentiometric titration data to calculate protonation constants. The analysis uses the variation of dV/dpH with titrant addition in terms of two physical parameters which involve the concentrations of H{sup +}, OH{sup -}, and H{sub m}A. The data for titration of acetic acid and 8-hydroxyquinoline in 0.10-5.0 m NaCl media are analyzed by this method to obtain the stoichiometric protonation constants of the acids, the ionization constants of water, and the parameters s and b in the pH electrode calibration equation, pcH = spH{sub m} + b, where pcH = -log[H{sup +}], pH{sub m} is the pH meter reading. 31 refs., 3 figs., 6 tabs.

Chen, J.F.; Xia, Y.X.; Choppin, G.R. [Florida State Univ., Tallahassee, FL (United States)] [Florida State Univ., Tallahassee, FL (United States)

1996-11-15

3

Simultaneous potentiometric determination of cationic and ethoxylated nonionic surfactants in liquid cleaners and disinfectants.  

PubMed

A sensitive potentiometric surfactant sensor based on a highly lipophilic 1,3-didecyl-2-methyl-imidazolium cation and a tetraphenylborate (TPB) antagonist ion was used as the end-point detector in ion-pair potentiometric surfactant titrations using sodium TPB as a titrant. Several analytical and technical grade cationic and ethoxylated nonionic surfactants (EONS) and mixtures of both were potentiometrically titrated. The sensor showed satisfactory analytical performances within a pH range of 3-10 and exhibited satisfactory selectivity for all CS and EONS investigated. Ionic strength did not influence the titration except at 0.1M NaCl, in which a slight distortion of the second inflexion corresponded with the nonionic surfactant. Two-component combinations of four CS and three EONS were potentiometrically titrated using the sensor previously mentioned as the end-point detector. The quantities of the surfactants varied between 2 and 6 ?mol for CS and 2.50 and 7.50 ?mol for EONS. The known addition methodology was used for determination of the surfactant with considerably lower concentration in the mixture. Three commercial products containing cationic surfactants as disinfectants and nonionic surfactants were potentiometrically titrated, and the results for both type of surfactants were compared with those obtained with standard conventional methods. PMID:21147321

Samardži?, Mirela; Sak-Bosnar, Milan; Maduni?-?a?i?, Dubravka

2011-01-15

4

Characterization of Sea Lettuce Surface Functional Groups by Potentiometric Titrations  

NASA Astrophysics Data System (ADS)

In pursuit of our ultimate goal to better understand the prodigious capacity of the marine macroalga Ulva lactuca (sea lettuce) for adsorbing a broad range of dissolved trace metals from seawater, we performed an initial characterization of its surface functional groups. Specifically, the number of distinct functional groups as well as their individual bulk concentrations and acid dissociation constants (pKas) were determined by potentiometric titrations in NaCl solutions of various ionic strengths (I = 0.01-5.0 M), under inert nitrogen atmosphere at 25°C. Depending on the ionic strength, Ulva samples were manually titrated down to pH 2 or 3 with 1 N HCl and then up to pH 10 with 1 N NaOH in steps of 0.1-0.2 units, continuously monitoring pH with a glass combination electrode. Titrations of a dehydrated Ulva standard reference material (BCR-279) were compared with fresh Ulva tissue cultured in our laboratory. A titration in filtered natural seawater was also compared with one in an NaCl solution of equal ionic strength. Equilibrium constants for the ionization of water in NaCl solutions as a function of ionic strength were obtained from the literature. Fits to the titration data ([H]T vs. pH) were performed with the FITEQL4.0 computer code using non-electrostatic 3-, 4-, and 5-site models, either by fixing ionic strength at its experimental value or by allowing it to be extrapolated to zero, while considering all functional group pKas and bulk concentrations as adjustable parameters. Since pKas and bulk concentrations were found to be strongly correlated, the latter were also fixed in some cases to further constrain the pKas. Whereas these calculations are currently ongoing, preliminary results point to three, possibly four, functional groups with pKas of about 4.1, 6.3, and 9.5 at I = 0. Bulk concentrations of the three groups are very similar, about 5-6×10-4 mol/g based on dry weight, which suggests that all are homogeneously distributed over the surface and probably part of a single macromolecular scaffold. Fresh Ulva tissue appears to contain the same three functional groups but at lower concentrations, based on wet weight. The titration in natural seawater was largely dominated by the non-carbonate alkalinity of the solution and could not be robustly modeled. Results of fits with ionic strengths fixed at their experimental values indicate that the pKas of all three groups display prominent Debije-Hückel-type behavior, hence that these acid dissociation reactions involve a different mechanism than metal-proton exchange reactions on mineral surfaces, whose distribution coefficients (i.e., equilibrium constants) generally show a weak ionic strength dependence.

Ebling, A. M.; Schijf, J.

2008-12-01

5

Simple home-made sensors for potentiometric titrations. [Nitroform CH(NO/sub 2/)/sub 3/  

SciTech Connect

A sensor for potentiometric titrations was prepared by coating a spectroscopic graphite rod with a solution of poly(vinyl chloride) and dioctyphthalate in tetrahydrofuran. The reference electrode was an Ag/AgCl single-junction electrode. The sensor was used in precipitation, acid-base, compleximetric, and redox titrations. Preparation of the coated-graphite sensor is simple and rapid. Moreover, it is quite inexpensive. A limitation is its applicability in aqueous media only, because organic solvents will dissolve the membrane. Various uncoated types of graphite have also been investigated as sensors, particularly in two applications of interest in the analysis of propellants: the titration of nitroform and perchlorate. Obviously, these sensors can be used also in nonaqueous, or partially nonaqueous media. These sensors may also find use in the potentiometric titration of fluoride vs La(III) or Th(IV).

Selig, W.

1982-04-01

6

A novel approach for high precision rapid potentiometric titrations: Application to hydrazine assay  

NASA Astrophysics Data System (ADS)

We propose a high precision rapid personal computer (PC) based potentiometric titration technique using a specially designed mini-cell to carry out redox titrations for assay of chemicals in quality control laboratories attached to industrial, R&D, and nuclear establishments. Using this technique a few microlitre of sample (50-100 ?l) in a total volume of ˜2 ml solution can be titrated and the waste generated after titration is extremely low comparing to that obtained from the conventional titration technique. The entire titration including online data acquisition followed by immediate offline analysis of data to get information about concentration of unknown sample is completed within a couple of minutes (about 2 min). This facility has been created using a new class of sensors, viz., pulsating sensors developed in-house. The basic concept in designing such instrument and the salient features of the titration device are presented in this paper. The performance of the titration facility was examined by conducting some of the high resolution redox titrations using dilute solutions--hydrazine against KIO3 in HCl medium, Fe(II) against Ce(IV) and uranium using Davies-Gray method. The precision of titrations using this innovative approach lies between 0.048% and 1.0% relative standard deviation in different redox titrations. With the evolution of this rapid PC based titrator it was possible to develop a simple but high precision potentiometric titration technique for quick determination of hydrazine in nuclear fuel dissolver solution in the context of reprocessing of spent nuclear fuel in fast breeder reactors.

Sahoo, P.; Malathi, N.; Ananthanarayanan, R.; Praveen, K.; Murali, N.

2011-11-01

7

An on-line potentiometric sequential injection titration process analyser for the determination of acetic acid.  

PubMed

An on-line potentiometric sequential injection titration process analyser for the determination of acetic acid is proposed. A solution of 0.1 mol L(-1) sodium chloride is used as carrier. Titration is achieved by aspirating acetic acid samples between two strong base-zone volumes into a holding coil and by channelling the stack of well-defined zones with flow reversal through a reaction coil to a potentiometric sensor where the peak widths were measured. A linear relationship between peak width and logarithm of the acid concentration was obtained in the range 1-9 g/100 mL. Vinegar samples were analysed without any sample pre-treatment. The method has a relative standard deviation of 0.4% with a sample frequency of 28 samples per hour. The results revealed good agreement between the proposed sequential injection and an automated batch titration method. PMID:12207255

van Staden, J F; Mashamba, Mulalo G; Stefan, Raluca I

2002-09-01

8

Concentration-related response potentiometric titrations to study the interaction of small molecules with large biomolecules.  

PubMed

In the present paper, the utility of a special potentiometric titration approach for recognition and calculation of biomolecule/small-molecule interactions is reported. This approach is fast, sensitive, reproducible, and inexpensive in comparison to the other methods for the determination of the association constant values (Ka) and the interaction energies (?G). The potentiometric titration measurement is based on the use of a classical polymeric membrane indicator electrode in a solution of the small-molecule ligand. The biomolecule is used as a titrant. The potential is measured versus a reference electrode and transformed into a concentration-related signal over the entire concentration interval, also at low concentrations, where the millivolt (y-axis) versus log canalyte (x-axis) potentiometric calibration curve is not linear. In the procedure, Ka is calculated for the interaction of cocaine with a cocaine binding aptamer and with an anticocaine antibody. To study the selectivity and cross-reactivity, other oligonucleotides and aptamers are tested, as well as other small ligand molecules such as tetrakis(4-chlorophenyl)borate, metergoline, lidocaine, and bromhexine. The calculated Ka compared favorably to the value reported in the literature using surface plasmon resonance. The potentiometric titration approach called "concentration-related response potentiometry" is used to study molecular interaction for seven macromolecular target molecules and four small-molecule ligands. PMID:25390494

Hamidi-Asl, Ezat; Daems, Devin; De Wael, Karolien; Van Camp, Guy; Nagels, Luc J

2014-12-16

9

Potentiometric titration of Co(II) in presence of Co(III).  

PubMed

A potentiometric titration for cobalt(II) determination in the presence of Co(III) based on the oxidation of Co(II) with Na(2)CrO(4) in ethylenediamine medium and back-titration of the oxidant excess with (NH(4))(2)Fe(SO(4))(2) in acid medium is described. The titration is monitored with a Pt indicator electrode and carried out until the greatest jump of potential from one drop of titrant appears. A RSD smaller than 1.5% has been obtained for 50-300 mumol Co(II). The method proposed was applied in the analysis of a new type electroless copper plating solutions containing Co(II)-ethylenediamine complex compounds as reducing agents. Cu(II), Co(III) and Cr(III) do not interfere in the determination of Co(II). PMID:18967436

Norkus, E

1998-12-01

10

Near infrared spectral changes of cytochrome aa3 during potentiometric titrations.  

PubMed Central

Singular value decomposition (SVD) was used to deconvolute the spectral changes occurring in the near infrared region during potentiometric titrations of cytochrome aa3. Overall oxidized minus reduced difference spectra revealed a broad absorbance feature centered near 830 nm with an apparent Em near 250 mV. However, SVD did not isolate any spectral species with an absorbance centered near 830 nm. It was found that the spectral changes occurring in the wavelength region from 650 to 950 nm were associated mainly with cytochromes a and a3. It was concluded that the absorbance at 830 nm should not be used as an independent measure of the concentration of CuA in cytochrome aa3. PMID:7696488

Hendler, R W; Harmon, P A; Levin, I W

1994-01-01

11

Uncertainty evaluation in the chloroquine phosphate potentiometric titration: application of three different approaches.  

PubMed

A measurement result cannot be properly interpreted if not accompanied by its uncertainty. Several methods to estimate uncertainty have been developed. From those methods three in particular were chosen in this work to estimate the uncertainty of the Eu. Ph. chloroquine phosphate assay, a potentiometric titration commonly used in medicinal control laboratories. The famous error-budget approach (also called bottom-up or step-by-step) described by the ISO Guide to the expression of Uncertainty in Measurement (GUM) was the first method chosen. It is based on the combination of uncertainty contributions that have to be directly derived from the measurement process. The second method employed was the Analytical Method Committee top-down which estimates uncertainty through reproducibility obtained during inter-laboratory studies. Data for its application were collected in a proficiency testing study carried out by over 50 laboratories throughout Europe. The last method chosen was the one proposed by Barwick and Ellison. It uses a combination of precision, trueness and ruggedness data to estimate uncertainty. These data were collected from a validation process specifically designed for uncertainty estimation. All the three approaches presented a distinctive set of advantages and drawbacks in their implementation. An expanded uncertainty of about 1% was assessed for the assay investigated. PMID:16870384

Rodomonte, Andrea Luca; Montinaro, Annalisa; Bartolomei, Monica

2006-09-11

12

Microcalorimetric and potentiometric titration studies on the adsorption of copper by extracellular polymeric substances (EPS), minerals and their composites.  

PubMed

Equilibrium adsorption experiments, isothermal titration calorimetry and potentiometric titration techniques were employed to investigate the adsorption of Cu(II) by extracellular polymeric substances (EPS) extracted from Pseudomonas putida X4, minerals (montmorillonite and goethite) and their composites. Compared with predicted values of Cu(II) adsorption on composites, the measured values of Cu(II) on EPS-montmorillonite composite increased, however, those on EPS-goethite composite decreased. Potentiometric titration results also showed that more surface sites were observed on EPS-montmorillonite composite and less reactive sites were found on EPS-goethite composite. The adsorption of Cu(II) on EPS molecules and their composites with minerals was an endothermic reaction, while that on minerals was exothermic. The positive values of enthalpy change (Delta H) and entropy change (DeltaS) for Cu(II) adsorption on EPS and mineral-EPS composites indicated that Cu(II) mainly interacts with carboxyl and phosphoryl groups as inner-sphere complexes on EPS molecules and their composites with minerals. PMID:20227874

Fang, Linchuan; Huang, Qiaoyun; Wei, Xing; Liang, Wei; Rong, Xinming; Chen, Wenli; Cai, Peng

2010-08-01

13

Titration  

NSDL National Science Digital Library

The purpose of this project is to construct a mathematical model describing the effects of titration, and then to use that model to determine the concentration and the identity of an acid in a solution by fitting the model to real titration data.

Smith, David

2002-01-16

14

Predicting proton titration in cationic micelle and bilayer environments  

NASA Astrophysics Data System (ADS)

Knowledge of the protonation behavior of pH-sensitive molecules in micelles and bilayers has significant implications in consumer product development and biomedical applications. However, the calculation of pKa's in such environments proves challenging using traditional structure-based calculations. Here we apply all-atom constant pH molecular dynamics with explicit ions and titratable water to calculate the pKa of a fatty acid molecule in a micelle of dodecyl trimethylammonium chloride and liquid as well as gel-phase bilayers of diethyl ester dimethylammonium chloride. Interestingly, the pKa of the fatty acid in the gel bilayer is 5.4, 0.4 units lower than that in the analogous liquid bilayer or micelle, despite the fact that the protonated carboxylic group is significantly more desolvated in the gel bilayer. This work illustrates the capability of all-atom constant pH molecular dynamics in capturing the delicate balance in the free energies of desolvation and Coulombic interactions. It also shows the importance of the explicit treatment of ions in sampling the protonation states. The ability to model dynamics of pH-responsive substrates in a bilayer environment is useful for improving fabric care products as well as our understanding of the side effects of anti-inflammatory drugs.

Morrow, Brian H.; Eike, David M.; Murch, Bruce P.; Koenig, Peter H.; Shen, Jana K.

2014-08-01

15

Improved methylene blue two-phase titration method for determining cationic surfactant concentration in high-salinity brine.  

PubMed

The methylene blue (MB) two-phase titration method is a rapid and efficient method for determining the concentrations of anionic surfactants. The point at which the aqueous and chloroform phases appear equally blue is called Epton's end point. However, many inorganic anions, e.g., Cl(-), NO3(-), Br(-), and I(-), can form ion pairs with MB(+) and interfere with Epton's end point, resulting in the failure of the MB two-phase titration in high-salinity brine. Here we present a method to extend the MB two-phase titration method for determining the concentration of various cationic surfactants in both deionized water and high-salinity brine (22% total dissolved solid). A colorless end point, at which the blue color is completely transferred from the aqueous phase to the chloroform phase, is proposed as titration end point. Light absorbance at the characteristic wavelength of MB is measured using a spectrophotometer. When the absorbance falls below a threshold value of 0.04, the aqueous phase is considered colorless, indicating that the end point has been reached. By using this improved method, the overall error for the titration of a permanent cationic surfactant, e.g., dodecyltrimethylammonium bromide, in deionized (DI) water and high-salinity brine is 1.274% and 1.322% with limits of detection (LOD) of 0.149 and 0.215 mM, respectively. Compared to the traditional acid-base titration method, the error of this improved method for a switchable cationic surfactant, e.g., tertiary amine surfactant (Ethomeen C12), is 2.22% in DI water and 0.106% with LOD of 0.369 and 0.439 mM, respectively. PMID:25365626

Cui, Leyu; Puerto, Maura; López-Salinas, José L; Biswal, Sibani L; Hirasaki, George J

2014-11-18

16

Mixtures of hydrogenated and fluorinated lactobionamide surfactants with cationic surfactants: study of hydrogenated and fluorinated chains miscibility through potentiometric techniques.  

PubMed

The work reported herein deals with the aqueous behavior of hydrocarbon and/or fluorocarbon ionic and nonionic surfactants mixtures. These mixtures were studied using potentiometric techniques in NaBr (0.1 mol L-1) aqueous solution as well as in pure water. Mixed micelles were formed from a cationic surfactant (dodecyl or tetradecyltrimethylammonium bromide respectively called DTABr or TTABr) and neutral lactobionamide surfactants bearing a hydrogenated dodecyl chain (H12Lac) or a fluorinated chain (CF3-(CF2)5-(CH2)2- or CF3-(CF2)7-(CH2)2-). We showed that concentrations of ionic and nonionic surfactants in the monomeric form as well as the composition of the mixed micelles can be specified thanks to a potentiometric technique. The complete characterization does not request any model of micellization a priori. The activities of the micellar phase constituents, as well as the free enthalpies of mixing, were calculated. The subsequent interpretation only relies on the experimental characterization. Comparison of the behaviors of the various systems with a model derived from the regular solution theory reveals the predominant part of electrostatic interactions in the micellization phenomenon. It also appears that the energy of interaction between hydrogenated and fluorinated chains is unfavorable to mixing and is of much lower magnitude than the electric charges interactions. PMID:17935362

Peyre, Véronique; Patil, Sandeep; Durand, Grégory; Pucci, Bernard

2007-11-01

17

Determination of pKa values of new phenacyl-piperidine derivatives by potentiometric titration method in aqueous medium at room temperature (25±0.5oC).  

PubMed

Dissociation constant (pKa) of ten novel phenacyl derivatives of piperidine were determined by potentiometric titration method in aqueous medium at room temperature (25 ±0.5°C). The sample solutions were prepared in deionized water with ionic strength 0.01M and titrated with 0.1M NaOH solution. In addition, ?G values were also calculated. Different prediction software programs were used to calculate pKa values too and compared to the experimentally observed pKa values. The experimental and theoretical values were found in close agreement. The results obtained in this research would help to predict the good absorption of the studied compounds and can be selected as lead molecules for the synthesis of CNS active agents because of their lipophilic nature especially compound VII. PMID:25015461

Zafar, Shaista; Akhtar, Shamim; Tariq, Talat; Mushtaq, Noushin; Akram, Arfa; Ahmed, Ahsaan; Arif, Muhammad; Naeem, Sabahat; Anwar, Sana

2014-07-01

18

The effects of O-substituents of hexahomotrioxacalix[3]arene on potentiometric discrimination between dopamine and biological organic/inorganic cations.  

PubMed

As an interesting type of molecular recognition at a membrane surface, the tri-O-acetic acid ester (host 2) of hexahomotrioxacalix[3]arene, when incorporated into poly(vinyl chloride) (PVC) liquid membranes, displays a high potentiometric selectivity for dopamine over, not only other catecholamines (noradrenaline, adrenaline), but also quaternary ammonium guests (tetramethylammonium, choline, and acetylcholine) and inorganic cations (Na+, K+, NH4+). Interestingly, changes in membrane potential based on the host-guest complexation of host 2 that were observed dopamine/inorganic cation selectivity were not displayed by the related hosts 3 and 4, which contain amide substituents. This paper describes our efforts to separately estimate the two factors contributing to the dopamine selectivities, i.e., the guest lipophilicity factor and the host-guest complexation factor, in an attempt to understand the effects of the O-substituents of these hosts. The potentiometric experiments showed that, although the guests had roughly equal lipophilicity, the electromotive force (EMF) response for dopamine by host 2 was excellent. Furthermore, host 2 displayed ca. a 20-fold stronger complexation for dopamine, compared to noradrenaline, adrenaline, K+, and NH4+ cations. These results indicate that the high potentiometric selectivity of the ion-selective electrode for dopamine mainly reflect, not the guest lipophilicity factor but the host-guest complexation factor. On the other hand, host 3 displayed ca. a 3000-fold stronger binding to Na+ than dopamine, thus explaining the reasons for the lower dopamine-selectivities of host 3 compared to host 2. It is interesting to note that the high potentiometric selectivities for dopamine were displayed by not only host 2 but also host 5, regardless of the simple structure of the O-substituents. PMID:17329883

Saijo, Ryosuke; Murakami, Hiroyuki; Tsunekawa, Saori; Imanishi, Souhei; Shirai, Naohiro; Ikeda, Shin-Ichi; Odashima, Kazunori

2007-03-01

19

On the binding of calcium by micelles composed of carboxy-modified pluronics measured by means of differential potentiometric titration and modeled with a self-consistent-field theory.  

PubMed

We perform differential potentiometric titration measurements for the binding of Ca2+ ions to micelles composed of the carboxylic acid end-standing Pluronic P85 block copolymer (i.e., CAE-85 (COOH-(EO)26-(PO)39-(EO)26-COOH)). Two different ion-selective electrodes (ISEs) are used to detect the free calcium concentration; the first ISE is an indicator electrode, and the second is a reference electrode. The titration is done by adding the block copolymers to a known solution of Ca2+ at neutral pH and high enough temperature (above the critical micellization temperature CMT) and various amount of added monovalent salt. By measuring the difference in the electromotive force between the two ISEs, the amount of Ca2+ that is bound by the micelles is calculated. This is then used to determine the binding constant of Ca2+ with the micelles, which is a missing parameter needed to perform molecular realistic self-consistent-field (SCF) calculations. It turns out that the micelles from block copolymer CAE-85 bind Ca2+ ions both electrostatically and specifically. The specific binding between Ca2+ and carboxylic groups in the corona of the micelles is modeled through the reaction equilibrium -COOCa+ <==> -COO- + Ca2+ with pKCa = 1.7 +/- 0.06. PMID:17154568

Lauw, Y; Leermakers, F A M; Cohen Stuart, M A; Pinheiro, J P; Custers, J P A; van den Broeke, L J P; Keurentjes, J T F

2006-12-19

20

UPTAKE OF METAL IONS BY A NEW CHELATING ION EXCHANGE RESIN. PART 3: PROTONATION CONSTANTS VIA POTENTIOMETRIC TITRATION AND SOLID STATE 31P NMR SPECTROSCOPY  

Microsoft Academic Search

A new chelating ion exchange resin which incorporates methylenediphosphonate, carboxylate, and sulfonate functional groups in a polystyrene-divinylbenzene matrix has been prepared. This resin exhibits exceptionally high affinity for polyvalent cations even from moderately acidic aqueous media. Metal ion coordination occurs primarily at the diphosphonate group with the secondary binding sites contributing to charge neutralization when necessary and possible, and to

K. L. Nash; P. G. Rickert; J. V. Muntean; S. D. Alexandratos

1994-01-01

21

Going Beyond, Going Further: Knives, Forks, and Beer Cans as Potentiometric Sensors.  

ERIC Educational Resources Information Center

Background information, materials needed, and procedures used are provided for potentiometric fluoride, halide, orthophosphate, and sulfate titrations. Typical results obtained are also provided for each type of titration. (JN)

Selig, Walter S.

1985-01-01

22

Coupled chemical processes at clay/electrolyte interface: a batch titration study of Na-montmorillonites.  

PubMed

The present work addresses the protolytic charge of montmorillonite, which occurs on the broken-bond sites at the particle edges. The purpose is to overcome the general difficulty arising in potentiometric titration due to coupled side reactions, which severely impede the titrant budget (partial dissolution of the clay and of secondary phases, hydrolysis and readsorption of dissolved species, cation exchange). Batch potentiometric titrations were carried out on the montmorillonite fractions extracted from two bentonites (MX80 and SWy2) to quantify their protolytic charge. The effects of equilibration time (24 h and 7 days), pH from 4 to 10, and ionic strength (0.1 and 0.01 mol L(-1)) were extensively studied for the MX80 sample. Quantification of dissolution was achieved by analysis of the equilibrium solutions for dissolved species and by La(3+) exchange of the readsorbed species. The results clearly show that secondary phases such as iron- or silica-rich minerals contribute to the dissolved species, according to the nature of the raw bentonite. Furthermore, readsorption affects significant amounts of dissolved species. The overconsumption of proton/hydroxide due to dissolution, readsorption, and hydrolysis of dissolved species was evaluated using a self-consistent thermodynamic calculation. The ability of such calculation to correct the raw titration curves in order to extract the titrable surface charge of montmorillonite was evaluated by comparison with the continuous titration procedure. Especially in the alkaline domain, correcting the raw batch titration curves for the measured side reactions failed to reproduce the continuous titration curves. These observations demonstrate the limitations of the batch titration method and the superiority of fast, continuous methods for quantifying the dissociable surface charge of clays. PMID:16777124

Duc, Myriam; Thomas, Fabien; Gaboriaud, Fabien

2006-08-15

23

The potentiometric determination of chlorine in organic compounds at the milligram and decimilligram level  

Microsoft Academic Search

Summary A rapid procedure for chlorine in milligram samples by a method combining thePregl microcombustion and theNorthrop potentiometric titration is described. Accuracy and precision are reported for 5 determinations on each of four test samples. Similar data are given for three water-soluble organic hydrochlorides where only the potentiometric titration part of the procedure is involved.

J. A. Kuck; Martha Daugherty; Doris K. Batdorf

1954-01-01

24

Differentiating nonaqueous titration of aspirin, acetaminophen, and salicylamide mixtures.  

PubMed

Mixtures containing aspirin, acetaminophen, and salicylamide were assayed potentiometrically by nonaqueous titration. The difference in pKa values for these weak acids was sufficient to permit successful differentiation. The titrant was tetrabutylammonium hydroxide, and the titration solvent was dimethylformamide. The procedure was applied to commercial dosage forms. PMID:1151713

Rhodes, H J; DeNardo, J J; Bode, D W; Blake, M I

1975-08-01

25

Studies on the solid acidity of heated and cation-exchanged montmorillonite using n-butylamine titration in non-aqueous system and diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy  

NASA Astrophysics Data System (ADS)

The effects of heating and cation exchange on the solid acidity of montmorillonite were investigated using n-butylamine titration in non-aqueous system and diffuse reflectance Fourier transform infrared spectroscopy. The number of total, Brønsted, and Lewis acid sites showed the same modulation tendency with increasing heating temperature, reaching a maximum at 120 °C and subsequently decreasing until it reaches a minimum at 600 °C. The Lewis acid sites result from unsaturated Al3+ cations, and their number increased with the heating temperature due to the dehydration and dehydroxylation of montmorillonite. The generation and evolution of Brønsted acidity were mainly related to interlayer-polarized water molecules. Water adsorbed on the unsaturated Al3+ ions also acted as a Brønsted acid. The acid strength of the Brønsted acid sites was dependent on the polarization ability of the exchangeable cation, the amount of interlayer water, and the degree of dissociation of the interlayer water coordinated to exchangeable cations. All cation-exchanged montmorillonites exhibited different numbers of acid sites and various distributions of acid strength. Brønsted acidity was predominant in Al3+-exchanged montmorillonite, whereas the Na+- and K+-exchanged montmorillonites showed predominantly Lewis acidity. Moreover, Mg2+- and Li+-exchanged montmorillonites exhibited approximately equal numbers of Brønsted and Lewis acid sites. The Brønsted acidity of cation-exchanged montmorillonite was positively correlated with the charge-to-radius ratios of the cations, whereas the Lewis acidity was highly dependent on the electronegativity of the cations. The acid strengths of Al3+- and Mg2+-exchanged montmorillonites were remarkably higher than those of monovalent cation-exchanged montmorillonites, showing the highest acid strength ( H 0 ? -3.0). Li+- and Na+-exchanged montmorillonites exhibited an acid strength distribution of -3.0 < H 0 ? 4.8, with the acid strength ranging primarily from 1.5 to 3.3 in Li+-exchanged montmorillonite, whereas only weaker-strength acid sites (1.5 < H 0 ? 4.8) were present in K+-exchanged montmorillonite. The results of the catalysis experiments indicated that montmorillonite promoted the thermal decomposition of the model organic. The catalytic activity showed a positive correlation with the solid acidity of montmorillonite and was affected by cation exchange, which occurs naturally in geological processes.

Liu, Hongmei; Liu, Dong; Yuan, Peng; Tan, Daoyong; Cai, Jingong; He, Hongping; Zhu, Jianxi; Song, Zhiguang

2013-06-01

26

Thermodynamic analysis of Bacillus subtilis endospore protonation using isothermal titration calorimetry  

NASA Astrophysics Data System (ADS)

Bacterial proton and metal adsorption reactions have the capacity to affect metal speciation and transport in aqueous environments. We coupled potentiometric titration and isothermal titration calorimetry (ITC) analyses to study Bacillus subtilis spore-proton adsorption. We modeled the potentiometric data using a four and five-site non-electrostatic surface complexation model (NE-SCM). Heats of spore surface protonation from coupled ITC analyses were used to determine site specific enthalpies of protonation based on NE-SCMs. The five-site model resulted in a substantially better model fit for the heats of protonation but did not significantly improve the potentiometric titration model fit. The improvement observed in the five-site protonation heat model suggests the presence of a highly exothermic protonation reaction circa pH 7 that cannot be resolved in the less sensitive potentiometric data. From the log Ks and enthalpies we calculated corresponding site specific entropies. Log Ks and site concentrations describing spore surface protonation are statistically equivalent to B. subtilis cell surface protonation constants. Spore surface protonation enthalpies, however, are more exothermic relative to cell based adsorption suggesting a different bonding environment. The thermodynamic parameters defined in this study provide insight on molecular scale spore-surface protonation reactions. Coupled ITC and potentiometric titrations can reveal highly exothermic, and possibly endothermic, adsorption reactions that are overshadowed in potentiometric models alone. Spore-proton adsorption NE-SCMs derived in this study provide a framework for future metal adsorption studies.

Harrold, Zoë R.; Gorman-Lewis, Drew

2013-05-01

27

Potentiometric determination of saccharin in commercial artificial sweeteners using a silver electrode  

Microsoft Academic Search

A simple, precise, rapid and low-cost potentiometric method for saccharin determination in commercial artificial sweeteners is proposed. Saccharin present in several samples of artificial sweeteners is potentiometrically titrated with silver nitrate solution using a silver wire as the indicator electrode, coupled to a titroprocessor. The best pH range was from 3.0 to 3.5 and the detection limit of sodium saccharin

João Carloni Filho; Alberto Oppermann Santini; Ana Lúcia M Nasser; Helena Redigolo Pezza; José Eduardo de Oliveira; Cristo Bladimiros Melios; Leonardo Pezza

2003-01-01

28

ChemTeacher: Titration  

NSDL National Science Digital Library

ChemTeacher compiles background information, videos, articles, demonstrations, worksheets and activities for high school teachers to use in their classrooms. The Titration page includes resources for teaching students about the theory and applications of titrations.

2012-07-24

29

Modern Directions for Potentiometric Sensors.  

PubMed

This paper gives an overview of the newest developments of polymeric membrane ion-selective electrodes. A short essence of the underlying theory is given, emphasizing how the electromotive force may be used to assess binding constants of the ionophore, and how the selectivity and detection limit are related to the underlying membrane processes. The recent developments in lowering the detection limits of ISEs are described, including recent approaches of developing all solid state ISEs, and breakthroughs in detecting ultra-small quantities of ions at low concentrations. These developments have paved the way to use potentiometric sensors as in ultra-sensitive affinity bioanalysis in conjunction with nanoparticle labels. Recent results establish that potentiometry compares favorably to electrochemical stripping analysis. Other new developments with ion-selective electrodes are also described, including the concept of backside calibration potentiometry, controlled current coulometry, pulsed chronopotentiometry, and localized flash titration with ion-selective membranes to design sensors for the direct detection of total acidity without net sample perturbation. These developments have further opened the field for exciting new possibilities and applications. PMID:19890473

Bakker, Eric; Chumbimuni-Torres, Karin

2008-01-01

30

Acid-base titrations for polyacids: Significance of the pK sub a and parameters in the Kern equation  

NASA Technical Reports Server (NTRS)

A new method is suggested for calculating the dissociation constants of polyvalent acids, especially polymeric acids. In qualitative form the most significant characteristics of the titration curves are demonstrated and identified which are obtained when titrating the solutions of such acids with a standard base potentiometrically.

Meites, L.

1978-01-01

31

Titanium (III) cation selective electrode based on synthesized tris(2pyridyl) methylamine ionophore and its application in water samples  

PubMed Central

The introduction of low detection limit ion selective electrodes (ISEs) may well pave the way for the determination of trace targets of cationic compounds. This research focuses on the detection of titanium (III) cation using a new PVC-membrane sensor based on synthesized tris(2pyridyl) methylamine (tpm) ionophore. The application and validation of the proposed sensor was done using potentiometric titration, inductively coupled plasma atomic emission spectrometry (ICP-AES), and atomic absorption spectrometry (AAS). The membrane sensor exhibited a Nernstian response to the titanium (III) cation over a concentration range of 1.0 × 10?6–1.0 × 10?2?M and pH range from 1–2.5. The Nernstian slope, the lower of detection (LOD), and the response time (t95%) of the proposed sensor were 29.17 ± 0.24?mV/dec, 7.9 × 10?7?M, and 20?s, respectively. The direct determination of 4–39??g/ml of titanium (III) standard solution showed an average recovery of 94.60 and a mean relative standard deviation of 1.8 at 100.0??g/ml. Finally, the utilization of the electrodes as end-point indicators for potentiometric titration with EDTA solutions for titanium (III) sensor was successfully carried out. PMID:24722576

Rezayi, Majid; Karazhian, Reza; Abdollahi, Yadollah; Narimani, Leila; Sany, Seyedeh Belin Tavakoly; Ahmadzadeh, Saeid; Alias, Yatimah

2014-01-01

32

Permian potentiometric analysis  

SciTech Connect

Pacific Northwest Laboratory (PNL) was requested to analyze potentiometric data from the Wolfcamp Formation of the Permian System to evaluate the recommendations by the University of Texas/Bureau of Economic Geology (UT/BEG) that additional geohydrologic boreholes be drilled into the Wolfcamp. The UT/BEG recommended that two stratigraphic and two geohydrologic borings be drilled into the Permian System during FY83 and that several shallow hydrologic tests be made in the Dockum Formation. A geostatistical technique known as kriging was applied to objectively evaluate these geohydrologic borehole recommendations. The Deaf Smith County location appears to be an excellent choice for a borehole. No high quality potentiometric data are available from Deaf Smith County and a borehole location immediately upgradient from the candidate repository site is needed. Adding this borehole location to the potentiometric data base will significantly reduce field data uncertainty near the location being studied. The Swisher County location does not appear to be the best choice. High quality data values H2206 and H2360 are located immediately upgradient from the proposed repository site. The best placement of additional geohydrological boreholes in the Wolfcamp Formation depends strongly upon the proposed repository location. The variability of the potentiometric data causes estimation errors to rapidly increase away from locations of field measurements. Suggested locations for additional boreholes for the Deaf Smith investigations are in northwest Randall or central Potter Counties. Ideal borehole locations for the Swisher county studies appear to be in southeast Randall and Armstrong Counties.

Devary, J.L.

1983-09-01

33

Processing and analysis of potentiometric data.  

PubMed Central

Potentiometric titration curves have traditionally been collected as the difference in absorbance at two wavelengths, and analyzed by plotting voltage vs. log (oxidized/reduced). The collection method, designed to monitor changes in local peak height, is effective for that purpose only when spectral backgrounds do not change slope as voltage changes, and the analysis method is valid only for a single isolated component (one whose midpoint potential is far from that of anything else in the mixture). Yet these methods are commonly used where such restrictions do not pertain, e.g. the study of cytochromes in mitonchondria. In this paper, we present more appropriate methods of collection and analysis, and suggest that, even with the best available methods, any conclusion should be confirmed in several ways. Experimental results are presented in accompanying papers. PMID:3697475

Shrager, R I; Hendler, R W

1986-01-01

34

Surfactant/detergent titration analysis method and apparatus for machine working fluids, surfactant-containing wastewater and the like  

DOEpatents

The present invention is an improved method and related apparatus for quantitatively analyzing machine working fluids and other aqueous compositions such as wastewater which contain various mixtures of cationic, neutral, and/or anionic surfactants, soluble soaps, and the like. The method utilizes a single-phase, non-aqueous, reactive titration composition containing water insoluble bismuth nitrate dissolved in glycerol for the titration reactant. The chemical reaction of the bismuth ion and glycerol with the surfactant in the test solutions results in formation of micelles, changes in micelle size, and the formation of insoluble bismuth soaps. These soaps are quantified by physical and chemical changes in the aqueous test solution. Both classical potentiometric analysis and turbidity measurements have been used as sensing techniques to determine the quantity of surfactant present in test solutions. This method is amenable to the analysis of various types of new, in-use, dirty or decomposed surfactants and detergents. It is a quick and efficient method utilizing a single-phase reaction without needing a separate extraction from the aqueous solution. It is adaptable to automated control with simple and reliable sensing methods. The method is applicable to a variety of compositions with concentrations from about 1% to about 10% weight. It is also applicable to the analysis of waste water containing surfactants with appropriate pre-treatments for concentration. 1 fig.

Smith, D.D.; Hiller, J.M.

1998-02-24

35

Surfactant/detergent titration analysis method and apparatus for machine working fluids, surfactant-containing wastewater and the like  

DOEpatents

The present invention is an improved method and related apparatus for quantitatively analyzing machine working fluids and other aqueous compositions such as wastewater which contain various mixtures of cationic, neutral, and/or anionic surfactants, soluble soaps, and the like. The method utilizes a single-phase, non-aqueous, reactive titration composition containing water insoluble bismuth nitrate dissolved in glycerol for the titration reactant. The chemical reaction of the bismuth ion and glycerol with the surfactant in the test solutions results in formation of micelles, changes in micelle size, and the formation of insoluble bismuth soaps. These soaps are quantified by physical and chemical changes in the aqueous test solution. Both classical potentiometric analysis and turbidity measurements have been used as sensing techniques to determine the quantity of surfactant present in test solutions. This method is amenable to the analysis of various types of new, in-use, dirty or decomposed surfactants and detergents. It is a quick and efficient method utilizing a single-phase reaction without needing a separate extraction from the aqueous solution. It is adaptable to automated control with simple and reliable sensing methods. The method is applicable to a variety of compositions with concentrations from about 1% to about 10% weight. It is also applicable to the analysis of waste water containing surfactants with appropriate pre-treatments for concentration.

Smith, Douglas D. (Knoxville, TN); Hiller, John M. (Oak Ridge, TN)

1998-01-01

36

Sorption modelling on illite Part I: Titration measurements and the sorption of Ni, Co, Eu and Sn  

NASA Astrophysics Data System (ADS)

In this study the physico-chemical, titration and sorption characteristics of Na-illite du Puy (Na-illite) have been measured and modelled. Samples of illite, collected in the region of le Puy-en-Velay, France, were purified and conditioned to the Na-form and physico-chemically characterised. Potentiometric titrations on suspensions of the Na-illite were carried out using a batch backtitration technique in 0.01, 0.1 and 0.5 M NaClO 4 background electrolytes from pH˜3 to ˜11.5 in an inert atmosphere glove box. The supernatant solutions from each titration experiment in each series were analysed for K, Mg, Ca, Sr, Si, Al, Fe and Mn. The titration data were modelled in terms of the protolysis of two amphoteric edge sites ( tbnd S W1OH and tbnd S W2OH) without an electrostatic term. Sorption edges (solid/liquid distribution ratios versus pH at trace sorbate concentrations and constant ionic strength) were determined for the transitions metals Ni(II) and Co(II), the lanthanide Eu(III), and the heavy metal Sn(IV) on Na-illite with NaClO 4 as the background electrolyte under anoxic conditions (CO 2 ? 2 ppm, O 2 ? 2 ppm). The study thus encompasses a broad range of metals with different thermodynamic characteristics and with valence states ranging from II to IV. The results from the modelling of the titration data, in combination with a non electrostatic surface complexation and cation exchange sorption model were applied to quantitatively describe the uptake characteristics of the metals listed above on Na-illite. Since sorption edges were measured at trace concentrations, metal uptake was modelled as occurring on strong type sites ( tbnd S SOH) only. This sorption model, the two site protolysis non electrostatic surface complexation and cation exchange model (2SPNE SC/CE model) had been previously developed and used to describe metal uptake on montmorillonite.

Bradbury, M. H.; Baeyens, B.

2009-02-01

37

A PC-based titrator for flow gradient titrations.  

PubMed

This paper describes a PC (personal computer) based titrator which was developed for gradient flow titrations. Concentration gradients were generated electrolytically or volumetrically in small tubes. Complete titration curves can be recorded on-line and evaluated automatically. The titrator can be used with all liquid flow detectors with low axial dispersion. The titrator was evaluated for the titration of thiosulphate with electrogenerated triiodide and for the titration of ammonia with electrogenerated hypobromite after continuous gas dialytic separation of ammonia from the sample solution. PMID:18924977

Fuhrmann, B; Spohn, U

1993-01-01

38

Dual potentiometric and UV\\/Vis spectrophotometric disposable sensors with dispersion cast polyaniline  

Microsoft Academic Search

Simple conducting polymer–polyaniline-based sensors\\/biosensors, working either in potentiometric or UV\\/Vis spectrophotometric\\u000a mode, are proposed. Disposable sensors were produced by coating polyaniline layers, cast from aqueous dispersion of the polymer\\u000a nanoparticles, on a transparent plastic polyacetate foil. In the potentiometric mode, polyaniline layers are sensitive to\\u000a a number of metal cations, while in UV\\/Vis mode, changes of absorbance were recorded only

Pawe? Malinowski; Iwona Grzegrzó?ka; Agata Michalska; Krzysztof Maksymiuk

2010-01-01

39

Filtrates & Residues: Olfactory Titration.  

ERIC Educational Resources Information Center

Presents an experiment that uses a unique acid-base indicator--the odor of raw onion--to indicate the end point of the titration of sodium hydroxide with hydrochloric acid. Allows the student to detect the completion of the neutralization reaction by olfaction rather than sight. (JRH)

Wood, John T.; Eddy, Roberta M.

1996-01-01

40

Micromechanical potentiometric sensors  

DOEpatents

A microcantilever potentiometric sensor utilized for detecting and measuring physical and chemical parameters in a sample of media is described. The microcantilevered spring element includes at least one chemical coating on a coated region, that accumulates a surface charge in response to hydrogen ions, redox potential, or ion concentrations in a sample of the media being monitored. The accumulation of surface charge on one surface of the microcantilever, with a differing surface charge on an opposing surface, creates a mechanical stress and a deflection of the spring element. One of a multitude of deflection detection methods may include the use of a laser light source focused on the microcantilever, with a photo-sensitive detector receiving reflected laser impulses. The microcantilevered spring element is approximately 1 to 100 .mu.m long, approximately 1 to 50 .mu.m wide, and approximately 0.3 to 3.0 .mu.m thick. An accuracy of detection of deflections of the cantilever is provided in the range of 0.01 nanometers of deflection. The microcantilever apparatus and a method of detection of parameters require only microliters of a sample to be placed on, or near the spring element surface. The method is extremely sensitive to the detection of the parameters to be measured.

Thundat, Thomas G. (Knoxville, TN)

2000-01-01

41

Surfactant titration of nanoparticle-protein corona.  

PubMed

Nanoparticles (NP), when exposed to biological fluids, are coated by specific proteins that form the so-called protein corona. While some adsorbing proteins exchange with the surroundings on a short time scale, described as a "dynamic" corona, others with higher affinity and long-lived interaction with the NP surface form a "hard" corona (HC), which is believed to mediate NP interaction with cellular machineries. In-depth NP protein corona characterization is therefore a necessary step in understanding the relationship between surface layer structure and biological outcomes. In the present work, we evaluate the protein composition and stability over time and we systematically challenge the formed complexes with surfactants. Each challenge is characterized through different physicochemical measurements (dynamic light scattering, ?-potential, and differential centrifugal sedimentation) alongside proteomic evaluation in titration type experiments (surfactant titration). 100 nm silicon oxide (Si) and 100 nm carboxylated polystyrene (PS-COOH) NPs cloaked by human plasma HC were titrated with 3-[(3-Cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS, zwitterionic), Triton X-100 (nonionic), sodium dodecyl sulfate (SDS, anionic), and dodecyltrimethylammonium bromide (DTAB, cationic) surfactants. Composition and density of HC together with size and ?-potential of NP-HC complexes were tracked at each step after surfactant titration. Results on Si NP-HC complexes showed that SDS removes most of the HC, while DTAB induces NP agglomeration. Analogous results were obtained for PS NP-HC complexes. Interestingly, CHAPS and Triton X-100, thanks to similar surface binding preferences, enable selective extraction of apolipoprotein AI (ApoAI) from Si NP hard coronas, leaving unaltered the dispersion physicochemical properties. These findings indicate that surfactant titration can enable the study of NP-HC stability through surfactant variation and also selective separation of certain proteins from the HC. This approach thus has an immediate analytical value as well as potential applications in HC engineering. PMID:25350777

Maiolo, Daniele; Bergese, Paolo; Mahon, Eugene; Dawson, Kenneth A; Monopoli, Marco P

2014-12-16

42

Studies on the acidity of mordenite and ZSM-5. 1. Determination of Broensted acid site concentrations in mordenite and ZSM-5 by conductometric titration  

SciTech Connect

The Broensted acidity of H-mordenite and H-ZSM-5 samples of varying proton concentration has been studied using aqueous conductometric titration, IR spectroscopy, and aqueous potentiometric titration. Good agreement is observed between Broensted acid site concentrations determined by conductometric titration and IR measurements, while indirect potentiometric titration affords acid site concentrations consistently lower than those measured using the conductometric technique. This finding is rationalized on the basis that, in a conductometric titration, all the accessible Broensted acid sites are direct;y titrated, whereas in the potentiometric procedure utilized, only those protons which can be ion-exchanged out of the zeolite are titrated. After allowing for the presence of extraframework aluminum in the zeolites (determined by [sup 27]Al NMR), the measured acidity for H-mordenite is found to increase linearly with increasing Al content within the range 0-1.5 mmol Al/g but appears to reach a limiting value at higher Al concentrations. For H-ZSM-5, the experimentally determined number of Broensted acid sites is also found to be linearly dependent on the Al molar fraction within the range measured (0-1.20 mmol Al/g). For both series of zeolite samples, the measured acidity is generally found to be less than the theoretical maximum calculated on the basis of an H[sup +]/Al ratio of 1. 43 refs., 10 figs., 4 tabs.

Crocker, M.; Herold, R.H.M.; Sonnemans, M.H.W.; Emeis, C.A.; Wilson, A.E.; Moolen, J.N. van der (Koninklijke/Shell-Laboratorium, Amsterdam (Netherlands))

1993-01-14

43

Effects of metal cations and fulvic acid on the adsorption of ciprofloxacin onto goethite.  

PubMed

Ciprofloxacin (CIP) can be strongly adsorbed by ferric oxides, but some influencing factors, such as multivalent cations and soil organic matter, have not been evaluated extensively. In this study, the interaction between CIP and four divalent metals (Ca, Cd, Cu, and Pb) was investigated using potentiometric titration and the results indicated that CIP can bind to the divalent metals in the following affinity order: Cu(II)?>?Pb(II)?>?Cd(II)?>?Ca(II). The effects of metals and fulvic acid (FA) on the adsorption behavior of CIP onto goethite surfaces were also examined using batch experiments. It was found that metal cations enhanced the CIP retention on goethite surfaces in the same order as the affinity order with CIP, indicating that metals likely increased CIP retention through cation bridging. FA was found to promote CIP sorption rather than compete with it, and the coexistence of FA and Cu(II) in the system exhibited an addictive effect with CIP sorption, indicating that they might influence the sorption separately under the studied loading condition. Taken together, our results suggested that the coexistence of divalent cations or soil organic matter will enhance CIP sorption on goethite surfaces, hence reducing its mobility and bioavailability in the environment. PMID:25096489

Tan, Yinyue; Guo, Yong; Gu, Xueyuan; Gu, Cheng

2015-01-01

44

Potentiometric studies at ORNL with hydrogen electrode concentration cells  

SciTech Connect

The absence of suitably stable reference electrodes for and to 300 C led ORNL to develop hydrogen electrode concentration cells for studies of equilibria of interest in reactor and steam generator systems to about 300 C during the late 1960`s and seventies. During the intervening two dozen years over twenty scientists have participated in potentiometric studies at Oak Ridge and much of that work will be summarized in this paper. A description of hydrogen electrode concentration cells developed in the late sixties and currently in use at Oak Ridge is given. The method of measurement, data interpretation, and published results are reviewed for studies of acid-base ionization, metal ion hydrolysis, and metal complexation reactions using principally such cells in titration or flow modes. 41 refs.

Mesmer, R.E.; Palmer, D.A.; Wesolowski, D.J. [Oak Ridge National Lab., TN (United States). Chemical and Analytical Sciences Div.

1994-12-31

45

In situ dissolution testing using potentiometric sensors  

Microsoft Academic Search

Potentiometric sensors can be used to determine the amount of API dissolved in the dissolution medium in function of time by measuring directly in the dissolution vessel of a Paddle (USP type 2) and Basket (USP type 1) apparatus. The prototype potentiometric sensor instrumentation showed very promising results for a selection of APIs with different physico-chemical properties. The applicability, benefits

Karl Peeters; Roy De Maesschalck; Hugo Bohets; Koen Vanhoutte; Luc Nagels

2008-01-01

46

Acid Strong Base Titrations Model  

NSDL National Science Digital Library

The Acid Strong Base Titrations model show how to estimate the concentration of the acid in a given sample. If one follows the titration by a visual indicator, the neutralization is detected through a sudden change of that indicator color. This model shows the titration curve as a strong monofunctional base (sodium hydroxide, for example), is added to an aqueous solution of a monoprotic acid. The Acid Strong Base Titrations model was developed using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the jar file will run the program if Java is installed. You can modify this simulation if you have EJS installed by right-clicking within the map and selecting "Open Ejs Model" from the pop-up menu item.

Fernandes, Fernando S.

2012-10-03

47

Design and construction of new potentiometric sensors for determination of Al(3+) ion based on (Z)-2-(2-methyl benzylidene)-1-(2,4-dinitrophenyl) hydrazine.  

PubMed

(Z)-2-(2-methyl benzylidene)-1-(2,4-dinitrophenyl) hydrazine (L) was used as an active component of PVC membrane electrode (PME), coated graphite electrode (CGE) and coated silver wire electrode (CWE) for sensing Al(3+) ion. The electrodes exhibited linear Nernstian responses to Al(3+) ion in the concentration range of 1.0×10(-6) to 1.0×10(-1)M (for PME, LOD=8.8×10(-7)M), 5.5×10(-7) to 2.0×10(-1)M (for CWE, LOD=3.3×10(-7)M) and 1.5×10(-7) to 1.0×10(-1)M (for CGE, LOD=9.2×10(-8)M). The best performances were observed with the membranes having the composition of L:PVC:NPOE:NaTPB in the ratio of 5:35:57:3 (w/w; mg). The electrodes have a response time of 6s and an applicable pH range of 3.5-9.1. The sensors have a lifetime of about 15weeks and exhibited excellent selectivity over a number of mono-, bi-, and tri-valent cations including alkali, alkaline earth metal, heavy and transition metal ions. Analytical utility of the proposed sensor has been further tested by using it as an indicator electrode in the potentiometric titration of Al(3+) with EDTA. The electrode was also successfully applied for the determination of Al(3+) ion in real and pharmaceutical samples. PMID:25687018

Mizani, F; Salmanzadeh Ardabili, S; Ganjaliab, M R; Faridbod, F; Payehghadr, M; Azmoodeh, M

2015-04-01

48

Amperometric, Bipotentiometric, and Coulometric Titration.  

ERIC Educational Resources Information Center

Reviews literature on amperometric, bipotentiometric, and coulometric titration methods examining: apparatus and methodology; acid-base reactions; precipitation and complexing reactions (considering methods involving silver, mercury, EDTA or analogous reagents, and other organic compounds); and oxidation-reduction reactions (considering methods…

Stock, John T.

1984-01-01

49

High-sensitivity titration microcalorimeter  

NASA Astrophysics Data System (ADS)

A differential titration microcalorimeter for studying intermolecular interactions in solutions has been designed. To increase the speed of the instrument, the dynamic correction method has been used. It has been shown that electrical calibration of the microcalorimeter is consistent with its chemical calibration. The use of the instrument for measuring the integral heats of dilution of 1-propanol has been demonstrated.

Velikov, A. A.; Grigoryev, S. V.; Chuikin, A. V.

2015-02-01

50

ChemTeacher Resource: Acid Base Titration  

NSDL National Science Digital Library

Acid-Base titration applet that plots pH changes as student adds acid or base. Gives choice of indicators. Compares plots for titration of traditional solution and a buffered solution. Can alter starting concentrations.

2012-07-30

51

Unique potentiometric detection systems for HPLC determination of some steroids in human urine.  

PubMed

Isocratic HPLC with potentiometric detection is used for the determination of some 17-ketosteroids (17-KS), e.g., androsterone, dehydroepiandrosterone and estrone, and their respective sulfated conjugates (17-KSS). Glassy carbon or composite electrodes containing a mixture of graphite and poly(vinyl chloride), PVC, were used as substrate electrodes. These substrates were covered either by montmorillonite or potassium tetrakis(p-chlorophenyl) borate containing PVC-based rubber phase membranes. The neutral 17-KS compounds were derivatized with Girard's reagent P (GP) to obtain cationic pyridinium acetohydrazones prior to the HPLC/potentiometric detection assay. No side reactions were observed, and the GP itself was not interfering. The method yielded accurate and reproducible results and was applicable to samples containing down to micromolar concentrations. Next, the 17-KSS compounds, acting as anionic charged molecules, were determined directly in human urine samples with the HPLC/potentiometry combination without preliminary derivatization. For this purpose, a new anion-sensitive potentiometric electrode was developed using a macrocyclic polyamine containing, PVC-based, rubber phase membrane. The three 17-KSS compounds were also determined accurately down to micromolar concentrations. Especially, the main androgen metabolites as dehydroepiandrosterone sulfate and androsterone sulfate could be selectively determined with a developed potentiometric sensor in human urine samples without time-consuming cleanup and preconcentration step. PMID:19156641

Vissers, Bert; Everaert, Joseph; Sekula, Justyna; Malak, Anna; Bohets, Hugo; Bazylak, Grzegorz; Nagels, Luc J

2009-01-01

52

Titration of an Unknown Acid or Base  

NSDL National Science Digital Library

This website contains a JAVA applet that simulates the titration of an unknown acid or base, and provides a graphical output of the titration curve. The unknown compounds are taken from a list of amino acids. Students set up the parameters of the titration, and then create a simulated pH curve. From this they are able to identify the unknown compound from the list, and determine the acid dissociation constant(s) from the titration data.

Blauch, David N.

2011-02-07

53

Schiff's Bases and Crown Ethers as Supramolecular Sensing Materials in the Construction of Potentiometric Membrane Sensors  

PubMed Central

Ionophore incorporated PVC membrane sensors are well-established analytical tools routinely used for the selective and direct measurement of a wide variety of different ions in complex biological and environmental samples. Potentiometric sensors have some outstanding advantages including simple design and operation, wide linear dynamic range, relatively fast response and rational selectivity. The vital component of such plasticized PVC members is the ionophore involved, defining the selectivity of the electrodes' complex formation. Molecular recognition causes the formation of many different supramolecules. Different types of supramolecules, like calixarenes, cyclodextrins and podands, have been used as a sensing material in the construction of ion selective sensors. Schiff's bases and crown ethers, which feature prominently in supramolecular chemistry, can be used as sensing materials in the construction of potentiometric ion selective electrodes. Up to now, more than 200 potentiometric membrane sensors for cations and anions based on Schiff's bases and crown ethers have been reported. In this review cation binding and anion complexes will be described. Liquid membrane sensors based on Schiff's bases and crown ethers will then be discussed.

Faridbod, Farnoush; Ganjali, Mohammad Reza; Dinarvand, Rassoul; Norouzi, Parviz; Riahi, Siavash

2008-01-01

54

Determination of polyhexamethylene biguanide hydrochloride using photometric colloidal titration with crystal violet as a color indicator.  

PubMed

A solution of polyhexamethylene biguanide hydrochloride (PHMB-HCl) was titrated with a standard solution of potassium poly(vinyl sulfate) (PVSK) using crystal violet (CV) as an photometric indicator cation. The end point was detected by a sharp absorbance change due to an abrupt decrease in the concentration of CV. A linear relationship between the concentration of PHMB-HCl and the end-point volume of the titrant existed in the concentration range from 2 to 10 × 10(-6) eq mol L(-1). Back-titration was based on adding an excess amount of PVSK to a sample solution containing CV, which was titrated with a standard solution of poly(diallyldimethylammonium chloride) (PDADMAC). The calibration curve of the PHMB-HCl concentration to the end point volume of the titrant was also linear in the concentration range from 2 to 8 × 10(-6) eq mol L(-1). Both photometric titrations were applied to the determination of PHMB-HCl in a few contact-lens detergents. Back-titration showed a clear end point, but direct titration showed an unclear end point. The results of the back-titration of PHMB-HCl were compared with the content registered in its labels. PMID:21828919

Masadome, Takashi; Miyanishi, Takaaki; Watanabe, Keita; Ueda, Hiroshi; Hattori, Toshiaki

2011-01-01

55

Endosomal escape and siRNA delivery with cationic shell crosslinked knedel-like nanoparticles with tunable buffering capacities  

PubMed Central

Cationic shell crosslinked knedel-like nanoparticles (cSCKs) have emerged as a highly efficient transfection agent for nucleic acids delivery. In this study, a new class of cSCKs with tunable buffering capacities has been developed by altering the amounts of histamines and primary amines incorporated into their crosslinked shell regions. The effect of histamine content of these nanoparticles with a hydrodynamic diameter of ca. 20 nm, on the siRNA-binding affinity, cytotoxicity, immunogenicity, and transfection efficiency was investigated. The modification of cSCKs with histamine was found to reduce the siRNA-binding affinity and cellular binding. On the other hand, it significantly reduced the toxicity and immunogenicity of the nanoparticles with subsequent increase in the transfection efficiency. In addition, escape from endosomes was facilitated by having two species of low and high pKas (i.e. histamine and primary amine groups, respectively), as demonstrated by the potentiometric titration experiments and the effect of bafilomycin A1, an inhibitor of the endosomal acidification, on the transfection efficiency of cSCKs. Histamine modification of 15 mol% was a threshold, above which cSCKs with higher histamine content completely lost the ability to bind siRNA and to transfect cells. This study highlights the potential of histamine incorporation to augment the gene silencing activity of cationic nanoparticles, reduce their toxicity, and increase their biocompatibility, which is of particular importance in the design of nucleic acids delivery vectors. PMID:22901966

Shrestha, Ritu; Elsabahy, Mahmoud; Florez-Malaver, Stephanie; Samarajeewa, Sandani; Wooley, Karen L.

2012-01-01

56

Surface Complexation of Neodymium at the Rutile-Water Interface: A Potentiometric and Modeling Study in NaCl Media to 250°C  

SciTech Connect

The adsorption of Nd{sup 3+} onto rutile surfaces was examined by potentiometric titration from 25 to 250 C, in 0.03 and 0.30m NaCl background electrolyte. Experimental results show that Nd{sup 3+} sorbs strongly, even at low temperature, with adsorption commencing below the pHznpc of rutile. In addition, there is a systematic increase in Nd{sup 3+} adsorption with increasing temperature. The experimental results were rationalized and described using surface oxygen proton affinities computed from the MUlti SIte Complexation or MUSIC model, coupled with a Stern-based three-layer description of the oxide/water interface. Moreover, molecular-scale information was incorporated successfully into the surface complexation model, providing a unique geometry for the adsorption of Nd{sup 3+} on rutile. The primary mode of Nd{sup 3+} adsorption was assumed to be the tetradentate configuration found for Y{sup 3+} adsorption on the rutile (110) surface from previously described in situ X-ray standing wave experiments, wherein the sorbing cations bond directly with two adjacent ''terminal'' and two adjacent ''bridging'' surface oxygen atoms. Similarly, the adsorption of Na{sup +} counterions was also assumed to be tetradentate, as supported by MD simulations of Na{sup +} interactions with the rutile (110) surface, and by analogous X-ray standing wave results for Rb{sup +} adsorption on rutile. Fitting parameters for Nd{sup 3+} adsorption included binding constants for the tetradentate adsorption complex and capacitance values for the inner-sphere binding plane. In addition, hydrolysis of the tetradentate adsorption complex was permitted and resulted in significantly improved model fits at higher temperature and pH values. The modeling results indicate that the Stern-based MUSIC surface-complexation model adequately accommodates molecular-scale information to uniquely rationalize and describe multivalent ion adsorption systematically into the hydrothermal regime.

Ridley, Mora K. [Texas Tech University, Lubbock; Machesky, Michael L. [Illinois State Water Survey, Champaign, IL; Wesolowski, David J [ORNL; Palmer, Donald [ORNL

2005-01-01

57

A Tabular Approach to Titration Calculations  

ERIC Educational Resources Information Center

Titrations are common laboratory exercises in high school and university chemistry courses, because they are easy, relatively inexpensive, and they illustrate a number of fundamental chemical principles. While students have little difficulty with calculations involving a single titration step, there is a significant leap in conceptual difficulty…

Lim, Kieran F.

2012-01-01

58

Flow Injection Potentiometric Assay of Hexoprenaline in Its Pure State, Pharmaceutical Preparations, and Biological Samples  

PubMed Central

Different hexoprenaline (Hx2SO4) conventional and coated wire electrodes were constructed and evaluated. Membranes were based on hexoprenalinium phosphotungstate (Hx-PTA) and hexporenalinium phosphomolybdate (Hx-PMA). The electrodes were fully characterized in terms of their composition, response time, life span, pH, and temperature and then were applied to the potentiometric determination of the hexoprenalinium ion in its pure state, pharmaceutical preparations, and biological samples, urine and plasma, under batch and flow injection conditions. The selectivity of the electrodes towards many inorganic cations, sugars, amino acids, and some other brochodilatures of close chemical composition was also tested. PMID:18483573

El-Nashar, Rasha M.

2008-01-01

59

High-temperature carbon monoxide potentiometric sensor  

Microsoft Academic Search

These sensors have been used in industrial alarm and control systems for monitoring and control of the oxygen concentration in a gas stream and for the control of air-fuel ratio in internal combustion engines as in automobiles. A high-temperature potentiometric CO sensor was developed by coating a mixture of CuO\\/ZnO over one of the platinum electrodes of a cell with

N. Li; T. C. Tan; H. C. Zeng

1993-01-01

60

Determination of sulphuric acid in process effluent streams using sequential injection titration.  

PubMed

Sulphuric acid in process effluent streams from an electrorefining copper plant was analysed with a sequential injection (SI) titration system using sodium hydroxide as titrant. In the proposed SI titration system a base titrant, acid analyte and base titrant zone were injected sequentially into a distilled water carrier stream in a holding coil and swept by flow reversal through a reaction coil to the detector. The base zones contained bromothymol blue as indicator and the endpoint was monitored spectrophotometrically at 620 nm. The influence of carrier stream flow rate, acid and base zone volumes and titrant concentration on the linear range of the method was studied to obtain an optimum. A linear relationship between peak width and logarithm of the acid concentration was obtained in the range 0.006-0.178 mol l(-1) of H(2)SO(4) for a NaOH concentration of 0.002 mol l(-1). The results obtained for the SI titration of process samples were in good agreement with a standard potentiometric method with an RSD<0.75% and a sample frequency of 23 samples h(-1). PMID:18967965

du Plessis, H; van Staden, J F

2000-05-31

61

Highly selective potentiometric and colorimetric determinations of cobalt (II) ion using thiazole based ligands.  

PubMed

New PVC-membrane electrodes were prepared by using 2-((thiazol-2-ylimino)methyl)phenol (L1) and 2-((thiazol-2-ylamino)methyl)phenol (L2) and explored as Co(II) selective electrodes. The effect of various plasticizers and anion excluder was studied in detail and improved performance was observed. It was found that the electrode based on L1 shows better response characteristics in comparison to L2. Optimum performance was observed for the membrane electrode having a composition of L1:NaTPB:DBP:PVC?2:8:78:62 (w/w, mg). The performance of PME based on L1 was compared with that of CGE. The electrodes exhibit Nernstian slope for Co(II) ions with a limit of detection of 6.91×10(-7)molL(-1) for PME and 7.94×10(-8)molL(-1) for CGE. The response time for PME and CGE was found to be 15s and 12s respectively. The potentiometric responses are independent in the pH range 3.0-9.0 for CGE. The CGE could be used for a period of 90days. The CGE was used as an indicator electrode in potentiometric titration of EDTA with Co(2+) ion. Further the selectivity of the L1 and L2 was also confirmed by the UV-vis and colorimetric studies and found that L1 is more selective for Co(II) ion. PMID:25491823

Singhal, Divya; Singh, Ashok Kumar; Upadhyay, Anjali

2014-12-01

62

Potentiometric Zinc Ion Sensor Based on Honeycomb-Like NiO Nanostructures  

PubMed Central

In this study honeycomb-like NiO nanostructures were grown on nickel foam by a simple hydrothermal growth method. The NiO nanostructures were characterized by field emission electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) techniques. The characterized NiO nanostructures were uniform, dense and polycrystalline in the crystal phase. In addition to this, the NiO nanostructures were used in the development of a zinc ion sensor electrode by functionalization with the highly selective zinc ion ionophore 12-crown-4. The developed zinc ion sensor electrode has shown a good linear potentiometric response for a wide range of zinc ion concentrations, ranging from 0.001 mM to 100 mM, with sensitivity of 36 mV/decade. The detection limit of the present zinc ion sensor was found to be 0.0005 mM and it also displays a fast response time of less than 10 s. The proposed zinc ion sensor electrode has also shown good reproducibility, repeatability, storage stability and selectivity. The zinc ion sensor based on the functionalized NiO nanostructures was also used as indicator electrode in potentiometric titrations and it has demonstrated an acceptable stoichiometric relationship for the determination of zinc ion in unknown samples. The NiO nanostructures-based zinc ion sensor has potential for analysing zinc ion in various industrial, clinical and other real samples. PMID:23202217

Abbasi, Mazhar Ali; Ibupoto, Zafar Hussain; Hussain, Mushtaque; Khan, Yaqoob; Khan, Azam; Nur, Omer; Willander, Magnus

2012-01-01

63

Theoretical considerations and a simple method for measuring alkalinity and acidity in low-pH waters by gran titration  

USGS Publications Warehouse

Titrations for alkalinity and acidity using the technique described by Gran (1952, Determination of the equivalence point in potentiometric titrations, Part II: The Analyst, v. 77, p. 661-671) have been employed in the analysis of low-pH natural waters. This report includes a synopsis of the theory and calculations associated with Gran's technique and presents a simple and inexpensive method for performing alkalinity and acidity determinations. However, potential sources of error introduced by the chemical character of some waters may limit the utility of Gran's technique. Therefore, the cost- and time-efficient method for performing alkalinity and acidity determinations described in this report is useful for exploring the suitability of Gran's technique in studies of water chemistry.

Barringer, J.L.; Johnsson, P.A.

1996-01-01

64

Beer classification by means of a potentiometric electronic tongue.  

PubMed

In this work, an electronic tongue (ET) system based on an array of potentiometric ion-selective electrodes (ISEs) for the discrimination of different commercial beer types is presented. The array was formed by 21 ISEs combining both cationic and anionic sensors with others with generic response. For this purpose beer samples were analyzed with the ET without any pretreatment rather than the smooth agitation of the samples with a magnetic stirrer in order to reduce the foaming of samples, which could interfere into the measurements. Then, the obtained responses were evaluated using two different pattern recognition methods, principal component analysis (PCA), which allowed identifying some initial patterns, and linear discriminant analysis (LDA) in order to achieve the correct recognition of sample varieties (81.9% accuracy). In the case of LDA, a stepwise inclusion method for variable selection based on Mahalanobis distance criteria was used to select the most discriminating variables. In this respect, the results showed that the use of supervised pattern recognition methods such as LDA is a good alternative for the resolution of complex identification situations. In addition, in order to show an ET quantitative application, beer alcohol content was predicted from the array data employing an artificial neural network model (root mean square error for testing subset was 0.131 abv). PMID:23870992

Cetó, Xavier; Gutiérrez-Capitán, Manuel; Calvo, Daniel; del Valle, Manel

2013-12-01

65

Actinide cation-cation complexes  

SciTech Connect

The +5 oxidation state of U, Np, Pu, and Am is a linear dioxo cation (AnO{sub 2}{sup +}) with a formal charge of +1. These cations form complexes with a variety of other cations, including actinide cations. Other oxidation states of actinides do not form these cation-cation complexes with any cation other than AnO{sub 2}{sup +}; therefore, cation-cation complexes indicate something unique about AnO{sub 2}{sup +} cations compared to actinide cations in general. The first cation-cation complex, NpO{sub 2}{sup +}{center_dot}UO{sub 2}{sup 2+}, was reported by Sullivan, Hindman, and Zielen in 1961. Of the four actinides that form AnO{sub 2}{sup +} species, the cation-cation complexes of NpO{sub 2}{sup +} have been studied most extensively while the other actinides have not. The only PuO{sub 2}{sup +} cation-cation complexes that have been studied are with Fe{sup 3+} and Cr{sup 3+} and neither one has had its equilibrium constant measured. Actinides have small molar absorptivities and cation-cation complexes have small equilibrium constants; therefore, to overcome these obstacles a sensitive technique is required. Spectroscopic techniques are used most often to study cation-cation complexes. Laser-Induced Photacoustic Spectroscopy equilibrium constants for the complexes NpO{sub 2}{sup +}{center_dot}UO{sub 2}{sup 2+}, NpO{sub 2}{sup +}{center_dot}Th{sup 4+}, PuO{sub 2}{sup +}{center_dot}UO{sub 2}{sup 2+}, and PuO{sub 2}{sup +}{center_dot}Th{sup 4+} at an ionic strength of 6 M using LIPAS are 2.4 {plus_minus} 0.2, 1.8 {plus_minus} 0.9, 2.2 {plus_minus} 1.5, and {approx}0.8 M{sup {minus}1}.

Stoyer, N.J. [Lawrence Berkeley Lab., CA (United States); Seaborg, G.T. [Lawrence Livermore National Lab., CA (United States)

1994-12-01

66

Micro coulometric titration in a liquid drop.  

PubMed

Miniaturized coulometric titration in a liquid drop has been investigated. Assays of ascorbic acid and thiosulfate with iodine titration were chosen as models. Constant volumes of falling liquid drops containing sample or reagent are manipulated via gravimetrical force to move along a slope hydrophobic path and directed to stop or to move out from an electrode. Such manipulation is useful for delivery of sample and reagents, in a way of flow without tubing. Electrochemical generation of titrant, in this case, iodine, is started at the electrode and micro coulometric titration can be performed in a drop by applying constant current. Timing in the titration can be made via naked eye with a stopwatch or via recording with a webcam camera connecting to a computer to detect the change due to the blue color complex of the excess iodine and starch. PMID:24054589

Kanyanee, Tinakorn; Fuekhad, Pongwasin; Grudpan, Kate

2013-10-15

67

Nanopore back titration analysis of dipicolinic acid.  

PubMed

Here, we report a novel label-free nanopore back titration method for the detection of dipicolinic acid, a marker molecule for bacterial spores. By competitive binding of the target analyte and a large ligand probe to metal ions, dipicolinic acid could be sensitively and selectively detected. This nanopore back titration approach should find useful applications in the detection of other species of medical, biological, or environmental importance if their direct detection is difficult to achieve. PMID:25074707

Han, Yujing; Zhou, Shuo; Wang, Liang; Guan, Xiyun

2015-02-01

68

Potentiometric flow injection analysis of mebeverine hydrochloride in serum and urine.  

PubMed

Four PVC membrane electrodes for the determination of mebeverine hydrochloride (MvCl) were fabricated and fully characterized in terms of composition, life span, usable pH range, working concentration range and temperature. The membranes of these electrodes consist of mebeverinium-silicotungstate (Mv-ST), silicomolybdate (Mv-SM), phosphotungstate (Mv-PT), or phosphomolybdate (Mv-PM) ion-associations dispersed in PVC matrix with dibutyl phthalate plasticizer. The electrodes showed near-Nernstian response over the concentration range of 4.0 x 10(-6) to 1.0 x 10(-2)M MvCl and were applied to the potentiometric determination of mebeverinium ion in pharmaceutical preparations, serum and urine in steady state and flow injection (FI) conditions with average recoveries of 96.4-102 % and relative standard deviations of 0.132-1.86%. The electrodes exhibit good selectivity for MvCl with respect to a large number of inorganic cations, organic cations, sugars and amino acids. The sensitivities of these electrodes are high enough to measure as low as 1.86 microg/ml of MvCl which permit the determination of the Ksp values of the ion-associates used. The proposed potentiometric methods offer the advantages of simplicity, accuracy, automation feasibility and applicability to turbid and colored sample solutions. PMID:15620532

Ibrahim, Hosny; Issa, Yousry M; Abu-Shawish, Hazem M

2005-01-01

69

Kinetics, thermodynamics and surface heterogeneity assessment of uranium(VI) adsorption onto cation exchange resin derived from a lignocellulosic residue  

NASA Astrophysics Data System (ADS)

A new cation exchange resin (PGTFS-COOH) having a carboxylate functional group at the chain end was prepared by grafting poly(hydroxyethylmethacrylate) onto tamarind fruit shell, TFS (a lignocellulosic residue) using potassium peroxydisulphate-sodium thiosulphate redox initiator, and in the presence of N,N'-methylenebisacrylamide (MBA) as a crosslinking agent, followed by functionalisation. The adsorbent was characterized with the help of FTIR, XRD, scanning electron micrographs (SEM), and potentiometric titrations. The kinetic and isotherm data, obtained at optimum pH value 6.0 at different temperatures could be fitted with pseudo-second-order equation and Sips isotherm model, respectively. An increase in temperature induces positive effect on the adsorption process. The calculated activation energy of adsorption ( Ea, 18.67 kJ/mol) indicates that U(VI) adsorption was largely due to diffusion-controlled process. The values of adsorption enthalpy, Gibbs free energy, and entropy were calculated using thermodynamic function relationships. The decrease in adsorption enthalpy with increasing U(VI) uploading on the adsorbent, reflects the surface energetic heterogeneity of the adsorbent. The isosteric heat of adsorption was quantitatively correlated with the fractional loading for the U(VI) ions adsorption onto PGTFS-COOH. The results showed that the PGTFS-COOH possessed heterogeneous surface with sorption sites having different activities.

Anirudhan, T. S.; Radhakrishnan, P. G.

2009-02-01

70

Light-scattering study of polyelectrolyte complex formation between anionic and cationic nanogels in an aqueous salt-free system.  

PubMed

We studied complex formation in an aqueous salt-free system (pH approximately 3 and at 25 degrees C) between nanogel particles having opposite charges. Anionic gel (AG) and cationic gel (CG) particles consist of lightly cross-linked N-isopropylacrylamide (NIPA) copolymers with 2-acrylamido-2-methylpropane sulfonic acid and with 1-vinylimidazole, respectively. The number of charges per particle was -4490 for AG and +20 300 for CG, as estimated from their molar masses (3.33 MD for AG and 11.7 MD for CG) by static light scattering (SLS) and their charge densities (1.35 mmol/g for AG and 1.74 mmol/g for CG) by potentiometric titration. The complexes were formed through the addition of AG to CG and vice versa using a turbidimetric titration technique. At the endpoint of the titration, the aggregate formed was a complex based upon stoichiometric charge neutralization: CG(n)()(+) + xAG(m)()(-) --> CG(n)()(+) (AG(m)()(-))(x)() where x = (n)()/(m)(). At different stages of the titration before the endpoint, the resulting complexes were examined in detail using dynamic light scattering, SLS, and electrophoretic light scattering (ELS). The main results are summarized as follows: (i) When AG with a hydrodynamic radius (R(h)) of 119 nm is added to CG (R(h) approximately 156 nm), the (R(h)) of the complex size decreases from 156 to 80 nm. (ii) In contrast to this (R(h)) change, the molar mass increases from 11.7 MD to 24 MD with increasing amounts of added AG. (iii) Upon addition of CG to AG, the complex formed has the same size ((R(h)) approximately 80 nm) and the same molar mass (55 +/- 2.5 MD) until 55 +/- 5% of AG has been consumed in the complexation. To understand these results, we used the following two models: the random model (RM), in which the added AG particles uniformly bind to all of the CG particles in the system via a strong electrostatic attraction, and the all-or-none model (AONM), in which part of the AG particles in the system preferably bind to the added CG particles to neutralize their electric charges but the other AG particles are uncomplexed and remain in the system. The complex formations upon addition of AG to CG and CG to AG were elucidated in terms of RM and AONM, respectively. PMID:16893235

Miyake, Masafumi; Ogawa, Kazuyoshi; Kokufuta, Etsuo

2006-08-15

71

A Monte Carlo Study of Titrating Polyelectrolytes  

E-print Network

A Monte Carlo Study of Titrating Polyelectrolytes Magnus Ullner y and Bo J¨onsson z Physical, Sweden Journal of Chemical Physics 104, 3048­3057 (1996) Monte Carlo simulations have been used to study of the polymer more difficult and biases the conformations towards more extended structures. In the Monte Carlo

Peterson, Carsten

72

A Monte Carlo Study of Titrating Polyelectrolytes  

E-print Network

A Monte Carlo Study of Titrating Polyelectrolytes Magnus Ullnery and Bo Jonssonz Physical Chemistry Journal of Chemical Physics 104, 3048-3057 (1996) Monte Carlo simulations have been used to study three di the conformations towards more extended structures. In the Monte Carlo simulations presented here, focus

Peterson, Carsten

73

Colorimetric Titration Experiment for the Undergraduate Laboratory.  

ERIC Educational Resources Information Center

Describes a colorimetric titration instrument usable in the undergraduate laboratory that fulfills the objectives of ruggedness, freedom from ambient light interference, and low cost. Although accessories can be added (raising the price), the basic instrument is low priced and can be used manually with a simple voltmeter. (JN)

Lopez, Edwin; Vassos, Basil H.

1984-01-01

74

Coulometric titration with gas diffusion separation step  

Microsoft Academic Search

Coulometric titration is employed in combination with a gas diffusion step for the quantitative separation and determination of volatile substances. Complete separation is brought about by filling the sample into a closed circulating loop and transporting it repeatedly past a microporous membrane. The combination of membrane separation module with the coulometric cell allows rapid separation and exploitation of the precise

M. Hahn; H. H. Rüttinger; H. Matschiner

1992-01-01

75

Isothermal Titration Calorimetry in the Student Laboratory  

ERIC Educational Resources Information Center

Isothermal titration calorimetry (ITC) is the measurement of the heat produced by the stepwise addition of one substance to another. It is a common experimental technique, for example, in pharmaceutical science, to measure equilibrium constants and reaction enthalpies. We describe a stirring device and an injection pump that can be used with a…

Wadso, Lars; Li, Yujing; Li, Xi

2011-01-01

76

Convergence-optimized procedure for applying the NICA-Donnan model to potentiometric titrations of humic substances.  

PubMed

Despite the high success of the NICA-Donnan (N-D) model to describe the interaction of protons and metal ions with natural organic matter, the large number of fit parameters is a major hindrance to its capacity to provide unique numerical solutions. This well-known difficulty is reflected in the unusually low value of the generic proton binding constant for carboxylic-type groups of fulvic acid (pK(H1) = 2.34), and to some extent of humic acid (2.93), and by the considerable covariance of the other generic N-D parameters. In some studies, the number of parameters obtained by regression is reduced by estimating some values independently with other techniques. Alternatively, the applicability of the model can be improved by devising a rigorous simulation procedure, which constrains the model-fit to converge toward chemically and physically realistic values. A procedure based on three successive iterations is proposed, and the solution is shown to be stable and invariant with the initial set of parameter values. The new generic parameters, in particular pK(H1)(FA) = 3.54 and pK(H1)(HA) = 3.87, derived from the same data set as the previous generic parameters, are in better agreement with literature data. PMID:20704219

Lenoir, Thomas; Matynia, Anthony; Manceau, Alain

2010-08-15

77

An Olfactory Indicator for Acid-Base Titrations.  

ERIC Educational Resources Information Center

The use of an olfactory acid-base indicator in titrations for visually impaired students is discussed. Potential olfactory indicators include eugenol, thymol, vanillin, and thiophenol. Titrations performed with each indicator with eugenol proved to be successful. (KR)

Flair, Mark N.; Setzer, William N.

1990-01-01

78

Effects of alkyl chain length and solvents on thermodynamic dissociation constants of the ionic liquids with one carboxyl group in the alkyl chain of imidazolium cations.  

PubMed

Thermodynamic dissociation constants of the Brønsted acidic ionic liquids (ILs) are important for their catalytic and separation applications. In this work, a series of imidazolium bromides with one carboxylic acid substitute group in their alkyl chain ([{(CH2)nCOOH}mim]Br, n = 1,3,5,7) have been synthesized, and their dissociation constants (pKa) at different ionic strengths have been determined in aqueous and aqueous organic solvents at 0.1 mole fraction (x) of ethanol, glycol, iso-propanol, and dimethyl sulfoxide by potentiometric titrations at 298.2 K. The standard thermodynamic dissociation constants (pKa(T)) of the ILs in these solvents were calculated from the extended Debye-Hückel equation. It was found that the pKa values increased with the increase of ionic strength of the media and of the addition of organic solvent in water. The pKa(T) values also increased with the increase of the alkyl chain length of cations of the ILs. In addition, the effect of solvent nature on pKa(T) values is interpreted from solvation of the dissociation components and their Gibbs energy of transfer from water to aqueous organic solutions. PMID:24720707

Chen, Yuehua; Wang, Huiyong; Wang, Jianji

2014-05-01

79

Choice of ion-selective electrodes in potentiometric determination of mercaptans and hydrogen sulfide in condensates  

SciTech Connect

Ion-selective electrodes for the potentiometric analysis of sulfur content of high-sulfur gas condensates from fields in the Caspian lowlands and West Siberia were evaluated. The membrane electrodes are based on silver sulfide in combination with tungsten, copper, cadmium, lead, zirconium, and platinum. Tests were also conducted for titrants that form stable compounds with mercaptans as well as for solvents that would be compatible with the condensates and not stratify when the titrants were added. Anion-selective electrodes included iodine-selective, sulfide-selective, and thiocyanate-selective; cation-selective electrodes were cadmium-selective, copper-selective, and lead-selective. The preferred titrant was found to be either a solution of ammoniacal silver nitrate in isopropanol or a solution of silver nitrate in DMFA. Reduction and poisoning behavior along with service life and sensitivity were assessed. The electrodes were field tested and the procedure has been implemented at the Karachaganak field.

Kiyanskii, V.V.; Burakhta, V.A.

1988-05-01

80

Kinetic Titration Series with Biolayer Interferometry  

PubMed Central

Biolayer interferometry is a method to analyze protein interactions in real-time. In this study, we illustrate the usefulness to quantitatively analyze high affinity protein ligand interactions employing a kinetic titration series for characterizing the interactions between two pairs of interaction patterns, in particular immunoglobulin G and protein G B1 as well as scFv IC16 and amyloid beta (1–42). Kinetic titration series are commonly used in surface plasmon resonance and involve sequential injections of analyte over a desired concentration range on a single ligand coated sensor chip without waiting for complete dissociation between the injections. We show that applying this method to biolayer interferometry is straightforward and i) circumvents problems in data evaluation caused by unavoidable sensor differences, ii) saves resources and iii) increases throughput if screening a multitude of different analyte/ligand combinations. PMID:25229647

Frenzel, Daniel; Willbold, Dieter

2014-01-01

81

Coulometric titration of urea with electrogenerated hypobromite.  

PubMed

A definitive method is described for the indirect assay of several tens of milligrams of urea by coulometric titration. Urea was decomposed in concentrated sulfuric acid using a Kjeldahl flask. Subsequently, the formed ammonium ion was titrated with electrogenerated hypobromite ion in a sodium bromide-sodium tetraborate medium of pH 8.6, with amperometric end-point detection. Parameters affecting the pretreatment procedure were evaluated. The optimized conditions included the heating of 2 g of urea at around 300°C for 2 h with 10 cm(3) of sulfuric acid. Under the proposed conditions, the assay value with expanded uncertainty (k = 2), 99.870 ± 0.026%, agreed well with the certified value of NIST SRM 912a urea, 99.9 ± 0.1%. PMID:23842420

Kato, Jun; Koseki, Takuma; Aoki, Yukie; Yamada, Ayako; Tanaka, Tatsuhiko

2013-01-01

82

Infrared titration of aqueous sulfuric acid  

Microsoft Academic Search

This paper presents the infrared (IR) titration of aqueous sulfuric acid solutions (0.50 M) obtained by the attenuated total reflection (ATR) sampling technique. After subtracting the water spectra, the spectra of the ionic species of HâSOâ in the 0--14 pH range were separated by factor analysis (FA) which also gave their abundance. The results were in agreement with the theoretical

Jean-Joseph Max; C. Menichelli; Camille Chapados

2000-01-01

83

Analysis of Cooperativity by Isothermal Titration Calorimetry  

PubMed Central

Cooperative binding pervades Nature. This review discusses the use of isothermal titration calorimetry (ITC) in the identification and characterisation of cooperativity in biological interactions. ITC has broad scope in the analysis of cooperativity as it determines binding stiochiometries, affinities and thermodynamic parameters, including enthalpy and entropy in a single experiment. Examples from the literature are used to demonstrate the applicability of ITC in the characterisation of cooperative systems. PMID:20111687

Brown, Alan

2009-01-01

84

LABORATORY EXPERIMENT 6 PRECIPITATION TITRATION WITH SILVER NITRATE.  

E-print Network

LABORATORY EXPERIMENT 6 PRECIPITATION TITRATION WITH SILVER NITRATE. The AgNO3 solution (~0.02 M in the titration of chloride ion with silver nitrate. The first excess of titrant results in the formation of a red Ag2CrO4. Calculations: From the volume of silver nitrate solution used fopr titration, calculate

Nazarenko, Alexander

85

Simple and Automated Coulometric Titration of Acid Using Nonisolated Electrodes  

ERIC Educational Resources Information Center

Coulometric titrations involve the quantification of analyte by measurements of current and time. In most coulometric titrations, the anode and cathode are placed in isolated cells that are connected by a salt bridge. By contrast, the experiments described here involve coulometric titrations (of acidic protons in solution) using a silver anode and…

Kuntzleman, Thomas S.; Kenney, Joshua B.; Hasbrouck, Scott; Collins, Michael J.; Amend, John R.

2011-01-01

86

Potentiometric Biosensor for Studying Hydroquinone Cytotoxicity in vitro  

PubMed Central

Many processes in living cells have electrochemical characteristics that are suitable for measurement by potentiometric biosensors. Potentiometric biosensors allow non invasive, real-time monitoring of the extracellular environment changes by measuring the potential at cell/sensor interface. This can be used as an indicator for overall cell cytotoxicity. The present work employs a potentiometric sensor array to investigate the cytotoxicity of hydroquinone to cultured mammalian V79 cells. Various electrode substrates (Au, PPy-HQ and PPy-PS) used for cell growth were designed and characterized. The controllable release of hydroquinone from PPy substrates was studied. Our results showed that hydroquinone exposure affected cell proliferation and delayed cell growth and attachment in a dose-dependent manner. Additionally, we have shown that exposure of V79 cells to hydroquinone at low doses (i.e 5?M) for more than 15 hours allows V79 cells to gain enhanced adaptability to survive exposure to high toxic HQ doses afterwards. Compared with traditional methods, the potentiometric biosensor not only provides non-invasive and real time monitoring of the cellular reactions but also is more sensitive for in vitro cytotoxicity study. By real time and non-invasive monitoring of the extracellular potential in vitro, the potentiometric sensor system represents a promising biosensor system for drug discovery. PMID:19926470

Wang, Yanyan; Chen, Qiang; Zeng, Xiangqun

2009-01-01

87

Titrimetric determination of iodide, hexacyanoferrate(ii), thiourea, cationic surfactants, and of picrate with a picrate ion-selective electrode  

Microsoft Academic Search

Summary Methods have been developed for the semiautomatic potentiometric precipitation titration of iodide, hexacyanoferrate(II), sulfide, and sulfide-thiourea mixtures with silver nitrate, of medically important quaternary ammonium compounds with sodium picrate, and of picrate ions with tetraphenylarsonium chloride, using a picrate ion-selective electrode. Semimicro and\\/or microamounts of these substances were determined with relative errors and relative standard deviations of 1–2%.

E. P. Diamandis; T. P. Hadjiioannou

1980-01-01

88

An exact definition of total alkalinity and a procedure for the estimation of alkalinity and total inorganic carbon from titration data  

NASA Astrophysics Data System (ADS)

The total (or titration) alkalinity of a natural water sample can be regarded as a measure of the proton deficit of the solution relative to an arbitrarily defined zero level of protons. The problem of unambiguously incorporating any particular acid-base system into the definition of alkalinity is thus the one of deciding which form to specify as the zero level of protons, and it is proposed that it be defined so that acids with a dissociation constant K > 10-4·5 (at 25°C and zero ionic strength) are considered as proton donors, whilst those bases formed from weak acids with K ? 10-4·5 are cosidered proton acceptors. A non-linear least squares procedure is suggested in order to estimate the total alkalinity (AT) and total inorganic carbon (CT) of a seawater sample from potentiometric titration data. The approach offers a significant conceptual improvement over the currently used refined Gran functions. In addition, an estimate of the statistical uncertainty of the estimated values of AT and CT is available. As it unnecessary to titrate beyond the alkalinity equivalence point, it may also be possible to speed up the titrations.

Dickson, A. G.

1981-06-01

89

Highly selective and sensitized spectrophotometric determination of iron (III) following potentiometric study.  

PubMed

A simple, selective and sensitized spectrophotometric method for determination of trace amounts of Fe3+ ion in tap and waste water solutions has been described. The spectrophotometric determination of Fe3+ ion using Ferron in the presence of N,N-Dodecytrimethylammonium bromide (DTAB) has been carried out. The Beer's law is obeyed over the concentration range of 0.05-2.6 microg mL(-1) of Fe3+ ion with the relative standard deviation (RSD %) <0.2% and the molar absorptivity of complexes in pH 3.5 is 3.8 x 10(3) L mol(-1) cm(-1). Potentiometric pH titration has been used for prediction of protonation constants of ferron, and evaluating its stoichiometry and respective stability constant with Fe3+ ion. As it is obvious the most likely species of ferron alone and its complexes are LH (log = 7.64), LH2 (logK = 10.52), LH3 (logK = 11.74) and ML2 (logbeta = 23.68), ML3 (logbeta = 23.68), ML3H (logbeta = 23.68), ML3H2 (logbta = 23.68) and ML(OH)2 (logbeta = 23.68) respectively. PMID:17970298

Shokrollahi, Ardeshir; Ghaedi, Mehrorang; Rajabi, Hamid Reza

2007-09-01

90

Amplified potentiometric transduction of DNA hybridization using ion-loaded Karin Y. Chumbimuni-Torres,a  

E-print Network

Amplified potentiometric transduction of DNA hybridization using ion-loaded liposomes Karin Y as an Advance Article on the web 28th May 2010 DOI: 10.1039/c0an00198h Amplified potentiometric transduction. The liposome-amplified potentiometric bioassay involved the duplex formation, followed by the capture

Zhang, Liangfang

91

Determination of lanthanum by flame photometric titration.  

PubMed

The flame emission of lanthanum at 560 mmu decreases linearly with phosphate concentration until a 1:1 molar ratio is reached, and then remains practically constant. Lanthanum can be titrated with phosphate, the equivalence point being detected from the change in emission intensity. Errors due to consumption of solution by the atomizer can be kept low by using short spraying times and low galvanometer damping. The average error is about -1% for 0.1M solutions and less than -5% for 0.01M. The method gives good results in the presence of titanium(III), zirconium, thorium and aluminium but cerium(III) and yttrium seriously interfere. PMID:18960392

Svehla, G; Slevin, P J

1968-09-01

92

Potentiometric sensing utilizing paper-based microfluidic sampling.  

PubMed

A new approach to potentiometric sensing utilizing paper-based microfluidic sampling is studied in this work. A solid-contact ion-selective electrode and a solid-contact reference electrode are pressed against a filter paper into which the sample solution is absorbed. The filter paper acts simultaneously as a sampling unit and as a sample container during potentiometric sensing. The paper substrates containing standard and sample solutions are disposable, while the sensors are used multiple times. The analytical method presented here opens new possibilities for economically and ecologically sound measurements of ions in various samples. PMID:24647405

Cui, Jingwen; Lisak, Grzegorz; Strzalkowska, Sylwia; Bobacka, Johan

2014-05-01

93

Potentiometric Sensors Based on Fluorous Membranes Doped with Highly Selective Ionophores for Carbonate  

PubMed Central

Manganese(III) complexes of three fluorophilic salen derivatives were used to prepare ion-selective electrodes (ISEs) with ionophore-doped fluorous sensing membranes. Because of their extremely low polarity and polarizability, fluorous media are not only chemically very inert but also solvate potentially interfering ions poorly, resulting in a much improved discrimination of such ions. Indeed, the new ISEs exhibited selectivities for CO32? that exceed those of previously reported ISEs based on non-fluorous membranes by several orders of magnitude. In particular, the interference from chloride and salicylate was reduced by two and six orders of magnitude, respectively. To achieve this, the selectivities of these ISEs were fine-tuned by addition of non-coordinating hydrophobic ions (i.e., ionic sites) into the sensing membranes. Stability constants of the anion–ionophore complexes were determined from the dependence of the potentiometric selectivities on the charge sign of the ionic sites and the molar ratio of ionic sites and the ionophore. For this purpose, a previously introduced fluorophilic tetraphenylborate and a novel fluorophilic cation with a bis(triphenylphosphoranylidene)ammonium group, (Rf6(CH2)3)3PN+P(Rf6(CH2)3)3, were utilized. The optimum CO32? selectivities were found for sensing membranes composed of anionic sites and ionophore in a 1:4 molar ratio, which results in the formation of 2:1 complexes with CO32? with stability constants up to 4.1 × 1015. As predicted by established theory, the site-to-ionophore ratios that provide optimum potentiometric selectivity depend on the stoichiometries of the complexes of both the primary and the interfering ions. However, the ionophores used in this study give examples of charges and stoichiometries previously neither explicitly predicted by theory nor shown by experiment. The exceptional selectivity of fluorous membranes doped with these carbonate ionophores suggests their use not only for potentiometric sensing but also for other types of sensors, such as the selective separation of carbonate from other anions and the sequestration of carbon dioxide. PMID:22070518

Chen, Li D.; Mandal, Debaprasad; Pozzi, Gianluca; Gladysz, John A.; Bühlmann, Philippe

2011-01-01

94

Direct spectrophotometric detection of the endpoint in metachromatic titration of polydiallyldimethylammonium chloride in water  

NASA Astrophysics Data System (ADS)

Polydiallyldimethylammonium chloride (poly-DADMAC) is a water soluble polymer that easily ionizes when dissolved in water. This cationic polyelectrolyte is mainly used as a flocculant within the water treatment industry, but little is known of its toxicological properties or its fate in the environment. It is often assumed that the polyelectrolyte sorbs onto solid surfaces in the water treatment stream and may be removed with the sludge or by a sand bed filter; which may not always be the case. In any event, reliable analytical techniques are needed for the determination of poly-DADMAC in matrices of environmental relevance. Metachromatic polyelectrolyte titration was used to quantify poly-DADMAC in model and tap water samples. We compared a routine visual titration method with a direct spectrophotometric technique that uses a dip probe, spectrometer, and computer. The direct spectrophotometric technique allowed for the determination of titration curves at 634 nm and 510 nm, whereby the later value has never been successfully utilised in the literature. The method simplifies the data analysis, and our recovery and matrix interference experiments demonstrate that the method is accurate, precise, and robust. The detection limit for this method was 0.1 mg L-1 in model water and 0.5 mg L-1 in tap water. The limit of quantification for both water matrices was 0.5 mg L-1.

Gumbi, B.; Ngila, J. C.; Ndungu, P. G.

95

Automated titration method for use on blended asphalts  

DOEpatents

A system for determining parameters and compatibility of a substance such as an asphalt or other petroleum substance uses titration to highly accurately determine one or more flocculation occurrences and is especially applicable to the determination or use of Heithaus parameters and optimal mixing of various asphalt stocks. In a preferred embodiment, automated titration in an oxygen gas exclusive system and further using spectrophotometric analysis (2-8) of solution turbidity is presented. A reversible titration technique enabling in-situ titration measurement of various solution concentrations is also presented.

Pauli, Adam T. (Cheyenne, WY); Robertson, Raymond E. (Laramie, WY); Branthaver, Jan F. (Chatham, IL); Schabron, John F. (Laramie, WY)

2012-08-07

96

Carboxylic Acid Unknowns and Titration 90 CARBOXYLIC ACID UNKNOWN  

E-print Network

Point/Boiling Point If your carboxylic acid is a solid, take its melting point. If it is a liquid, take its micro- boiling point. C. Titration/Neutralization EquivalenceMolecular Weight Determination WeighCarboxylic Acid Unknowns and Titration 90 CARBOXYLIC ACID UNKNOWN A. Solubility Tests: Water, Na

Jasperse, Craig P.

97

Optical Sensors for Manual and Automatic Titration in Undergraduate Laboratory  

Microsoft Academic Search

The classic undergraduate titration analysis is upgraded using instrumental detection of end point with color indicators. Several color sensors (CCD-based spectrophotometer, video camera with RGB digitalization, photodiode with appropriate filters) were tested in order to replace the visual indication of the end point with different indicators. The developed procedures show adequate characteristics such as a short titration time and accuracy

Alexander Y. Nazarenko

2010-01-01

98

Quantitative Analysis of Sulfate in Water by Indirect EDTA Titration  

ERIC Educational Resources Information Center

The determination of sulfate concentration in water by indirect EDTA titration is an instructive experiment that is easily implemented in an analytical chemistry laboratory course. A water sample is treated with excess barium chloride to precipitate sulfate ions as BaSO[subscript 4](s). The unprecipitated barium ions are then titrated with EDTA.…

Belle-Oudry, Deirdre

2008-01-01

99

A Closer Look at Acid-Base Olfactory Titrations  

ERIC Educational Resources Information Center

Olfactory titrations using raw onions and eugenol as acid-base indicators are reported. An in-depth investigation on olfactory titrations is presented to include requirements for potential olfactory indicators and protocols for using garlic, onions, and vanillin as acid-base olfactory indicators are tested.

Neppel, Kerry; Oliver-Hoyo, Maria T.; Queen, Connie; Reed, Nicole

2005-01-01

100

Microscale pH Titrations Using an Automatic Pipet.  

ERIC Educational Resources Information Center

Presents a microscale pH titration technique that utilizes an automatic pipet. A small aliquot (1-5 mL) of the analyte solution is titrated with repeated additions of titrant, and the pH is determined after each delivery. The equivalence point is determined graphically by either the second derivative method or a Gran plot. The pipet can be…

Flint, Edward B.; Kortz, Carrie L.; Taylor, Max A.

2002-01-01

101

pH Static Titration: A Quasistatic Approach  

ERIC Educational Resources Information Center

The pH-static titration is applicable to those systems where at least two types of reactions occur in comparable intensities. The commonalities in titrimetric procedure realized according to pH-static titration, irrespective of the kind of chemical processes occurring are discussed.

Michalowski, Tadeusz; Toporek, Marcin; Rymanowski, Maciej

2007-01-01

102

Spectrophotometric Titration of a Mixture of Calcium and Magnesium.  

ERIC Educational Resources Information Center

Describes a spectrophotometric titration experiment which uses a manual titration spectrophotometer and manually operated buret, rather than special instrumentation. Identifies the equipment, materials, and procedures needed for the completion of the experiment. Recommends the use of this experiment in introductory quantitative analysis…

Fulton, Robert; And Others

1986-01-01

103

Students' integration of multiple representations in a titration experiment  

NASA Astrophysics Data System (ADS)

A complete understanding of a chemical concept is dependent upon a student's ability to understand the microscopic or particulate nature of the phenomenon and integrate the microscopic, symbolic, and macroscopic representations of the phenomenon. Acid-base chemistry is a general chemistry topic requiring students to understand the topics of chemical reactions, solutions, and equilibrium presented earlier in the course. In this study, twenty-five student volunteers from a second semester general chemistry course completed two interviews. The first interview was completed prior to any classroom instruction on acids and bases. The second interview took place after classroom instruction, a prelab activity consisting of a titration calculation worksheet, a titration computer simulation, or a microscopic level animation of a titration, and two microcomputer-based laboratory (MBL) titration experiments. During the interviews, participants were asked to define and describe acid-base concepts and in the second interview they also drew the microscopic representations of four stages in an acid-base titration. An analysis of the data showed that participants had integrated the three representations of an acid-base titration to varying degrees. While some participants showed complete understanding of acids, bases, titrations, and solution chemistry, other participants showed several alternative conceptions concerning strong acid and base dissociation, the formation of titration products, and the dissociation of soluble salts. Before instruction, participants' definitions of acid, base, and pH were brief and consisted of descriptive terms. After instruction, the definitions were more scientific and reflected the definitions presented during classroom instruction.

Kunze, Nicole M.

104

Characterization of Petroleum Sulfonates by a Nonaqueous Titration Method  

Microsoft Academic Search

A new method is described for the determination of the equivalent weight for petroleum sulfonates. The method is based on the direct acidimetric titration of the sulfonate in acetic acid\\/acetic anhydride solvent using a titrant of perchloric acid in dioxane. From the titration, the moles of perchloric acid required to react with the sulfonate is measured. The equivalent weight is

Kim Voss; Clark Bricker; M. J. Michnick; G. P. Willhite

1981-01-01

105

Titration and hysteresis in epigenetic chromatin silencing  

NASA Astrophysics Data System (ADS)

Epigenetic mechanisms of silencing via heritable chromatin modifications play a major role in gene regulation and cell fate specification. We consider a model of epigenetic chromatin silencing in budding yeast and study the bifurcation diagram and characterize the bistable and the monostable regimes. The main focus of this paper is to examine how the perturbations altering the activity of histone modifying enzymes affect the epigenetic states. We analyze the implications of having the total number of silencing proteins, given by the sum of proteins bound to the nucleosomes and the ones available in the ambient, to be constant. This constraint couples different regions of chromatin through the shared reservoir of ambient silencing proteins. We show that the response of the system to perturbations depends dramatically on the titration effect caused by the above constraint. In particular, for a certain range of overall abundance of silencing proteins, the hysteresis loop changes qualitatively with certain jump replaced by continuous merger of different states. In addition, we find a nonmonotonic dependence of gene expression on the rate of histone deacetylation activity of Sir2. We discuss how these qualitative predictions of our model could be compared with experimental studies of the yeast system under anti-silencing drugs.

Dayarian, Adel; Sengupta, Anirvan M.

2013-06-01

106

Potentiometric aptasensing of Listeria monocytogenes using protamine as an indicator.  

PubMed

Exposure to pathogens in recreational or drinking water is a serious public health concern. It is important to rapidly determine and identify trace levels of pathogens in real environmental samples. We report here on a label-free potentiometric aptasensor for rapid, sensitive, and selective detection of Listeria monocytogenes (LM), a pathogen widely distributed in the environment. An aptamer binds specifically to internalin A, a surface protein present in LM cells. The target-binding event prevents the aptamer from electrostatically interacting with protamine, which can be sensitively detected using a polycation-sensitive membrane electrode. Using this method, LM can be detected down to 10 CFU mL(-1). Coupled to an online filtration system, the bioassay has been evaluated with spiked coastal seawater samples and shows good recovery and high accuracy. This work demonstrates the possibility of developing potentiometric aptasensors for determination and identification of various bacteria in environmental samples. PMID:25220163

Ding, Jiawang; Lei, Jiahong; Ma, Xia; Gong, Jun; Qin, Wei

2014-10-01

107

Porous silicon as a substrate material for potentiometric biosensors  

NASA Astrophysics Data System (ADS)

For the first time porous silicon has been investigated for the purpose of application as a substrate material for potentiometric biosensors operating in aqueous solutions. Porous silicon was prepared from differently doped silicon substrates by a standard anodic etching process. After oxidation, penicillinase, an enzyme sensitive to penicillin, was bound to the porous structure by physical adsorption. To characterize the electrochemical properties of the so build up penicillin biosensor, capacitance - voltage (C - V) measurements were performed on these field-effect structures.

Thust, Marion; Schöning, M. J.; Frohnhoff, S.; Arens-Fischer, R.; Kordos, P.; Lüth, H.

1996-01-01

108

Automated potentiometric electrolyte analysis system. [for use in weightlessness  

NASA Technical Reports Server (NTRS)

The feasibility is demonstrated of utilizing chemical sensing electrode technology as the basis for an automatically-controlled system for blood gas and electrolyte analyses under weightlessness conditions. The specific measurements required were pH, pCO2, sodium, chloride, potassium ions, and ionized calcium. The general electrode theory, and ion activity measurements are described along with the fluid transport package, electronics unit, and controller for the automated potentiometric analysis system.

1973-01-01

109

Potentiometric-surface map, 1993, Yucca Mountain and vicinity, Nevada  

SciTech Connect

The revised potentiometric surface map here, using mainly 1993 average water levels, updates earlier maps of this area. Water levels are contoured with 20-m intervals, with additional 0.5-m contours in the small-gradient area SE of Yucca Mountain. Water levels range from 728 m above sea level SE of Yucca to 1,034 m above sea level north of Yucca. Potentiometric levels in the deeper parts of the volcanic rock aquifer range from 730 to 785 m above sea level. The potentiometric surface can be divided into 3 regions: A small gradient area E and SE of Yucca, a moderate-gradient area on the west side of Yucca, and a large-gradient area to the N-NE of Yucca. Water levels from wells at Yucca were examined for yearly trends (1986-93) using linear least-squares regression. Of the 22 wells, three had significant positive trends. The trend in well UE-25 WT-3 may be influenced by monitoring equipment problems. Tends in USW WT-7 and USW WTS-10 are similar; both are located near a fault west of Yucca; however another well near that fault exhibited no significant trend.

Tucci, P.; Burkhardt, D.J.

1995-12-31

110

Potentiometric surface of the Ozark aquifer in northern Arkansas, 2004  

USGS Publications Warehouse

The Ozark aquifer in northern Arkansas comprises dolomites, limestones, sandstones, and shales of Late Cambrian to Middle Devonian age, and ranges in thickness from approximately 1,100 feet to more than 4,000 feet. Hydrologically, the aquifer is complex, characterized by discrete and discontinuous flow components with large variations in permeability. The potentiometric-surface map, based on 59 well and 5 spring water-level measurements collected in 2004 in Arkansas and Missouri, indicates maximum water-level altitudes of about 1,188 feet in Benton County and minimum water-level altitudes of about 116 feet in Randolph County. Regionally, the flow within the aquifer is to the south and southeast in the eastern and central part of the study area and to the northwest and north in the western part of the study area. Comparing the 2004 potentiometric- surface map with a predevelopment potentiometricsurface map indicates general agreement between the two surfaces. Potentiometric-surface differences could be attributed to differences in pumping related to changing population from 1990 to 2000, change in source for public supplies, processes or water use outside the study area, or differences in data-collection or map-construction methods.

Schrader, T.P.

2005-01-01

111

Microprocessor-controlled system for automatic acquisition of potentiometric data and their non-linear least-squares fit in equilibrium studies.  

PubMed

A microprocessor-controlled potentiometric titration apparatus for equilibrium studies is described. The microprocessor controls the stepwise addition of reagent, monitors the pH until it becomes constant and stores the constant value. The data are recorded on magnetic tape by a cassette recorder with an RS232 input-output interface. A non-linear least-squares program based on Marquardt's modification of the Newton-Gauss method is discussed and its performance in the calculation of equilibrium constants is exemplified. An HP 9821 desk-top computer accepts the data from the magnetic tape recorder. In addition to a fully automatic fitting procedure, the program allows manual adjustment of the parameters. Three examples are discussed with regard to performance and reproducibility. PMID:18962716

Gampp, H; Maeder, M; Zuberbühler, A D; Kaden, T A

1980-06-01

112

A potentiometric study of the hydrolysis of ethylenediaminetetraacetic acid to 150{degrees}C  

SciTech Connect

Ethylenediaminetetraacetate anions, EDTA{sup 4-}, were titrated in a hydrogen-electrode concentration cell with an acidic titrant from 0 to 150{degrees}C at 25{degrees}C intervals. These titrations were carried out in the presence of 0. 1, 0.2, and 1.0 mol{center_dot}kg{sup -1} with the supporting electrolytes, sodium chloride, NaCl, and 1.0 mol{center_dot}kg{sup -1} tetramethylammonium trifluoromethylsulfonate, (CH{sub 3}){sub 4}N(F{sub 3}CSO{sub 3}) {l_brace}TMATFMS{r_brace} in order to assess the effect of both cation complexation by EDTA{sup 4-} and anion activity coefficient variations. The resulting hydrolysis quotients are discussed with reference to applications in boiler and heat exchanger chemical cleaning, as well as chemical and nuclear waste containment. Some recent diverse uses of this emf technique that also pertain to these applications will be mentioned briefly, e.g., surface absorption - zero-point-of-charge - measurements to high temperatures and in situ pH measurements in solubility and kinetic experiments.

Palmer, D.A. [Oak Ridge National Lab., TN (United States); Nguyen-Trung, Chinh [CREGU, Vandoeuvre les Nancy (France)

1995-02-01

113

Preliminary potentiometric map and flow dynamic characteristics for the upper-basalt confined aquifer system  

SciTech Connect

This report presents the first comprehensive Hanford Site-wide potentiometric map for the upper-basalt confined aquifer system (i.e., the upper Saddle Mountains Basalt). In constructing the potentiometric map, over forty on-site and off-site monitoring wells and boreholes were used. The potentiometric map developed for the upper-basalt confined aquifer is consistent with the areal head pattern indicated for the Mabton interbed, which is a deeper and more areally extensive confined aquifer underlying the Hanford Site. Salient features for the upper-basalt confined aquifer system potentiometric map are described.

Spane, F.A. Jr.; Raymond, R.G.

1993-09-01

114

Automatic photometric titrations of calcium and magnesium in carbonate rocks  

USGS Publications Warehouse

Rapid nonsubjective methods have been developed for the determination of calcium and magnesium in carbonate rocks. From a single solution of the sample, calcium is titrated directly, and magnesium is titrated after a rapid removal of R2O3 and precipitation of calcium as the tungstate. A concentrated and a dilute solution of disodium ethylenediamine tetraacetate are used as titrants. The concentrated solution is added almost to the end point, then the weak solution is added in an automatic titrator to determine the end point precisely.

Shapiro, L.; Brannock, W.W.

1955-01-01

115

Performance Evaluation of a Novel Potentiometric Membrane Sensor for Determination of Atorvastatin in Pharmaceutical Preparations  

PubMed Central

A novel potentiometric ion-selective PVC membrane sensor for analysis of atorvastatin (AT) in pharmaceutical preparations based on atorvastatin-(tetraphenyl borate), (AT-(TPB)2) as sensing element, tetraphenyl borate as additive and tris-2-ethyl-hexyl phosphate (TOP) as plasticizer solvent was prepared. The electrode shows a good Nernestian response over the concentration range of 0.09–5586 ?g mL-1of AT with slope of 30.1±0.1 mV/decade and limit of detection0.056?g mL-1.The response time of sensor is fats (less than 10 sec) and could be used for about one month in the pH range of 4.5–8.0. The electrode exhibit good selectivity for the AT in the presence of large amount of co-drugs and inorganic cations. The method is precise and accurate with mean relative standard deviation of <2%.Atorvastatin is determined successfully in several tablets by the proposed membrane. PMID:24523744

Ahmadi, Farhad; Asaadi, Nasim

2013-01-01

116

On the indirect polyelectrolyte titration of cellulosic fibers. Conditions for charge stoichiometry and comparison with ESCA.  

PubMed

The effect of electrolyte (NaHCO3) concentration on the adsorption of poly-DADMAC (poly-diallyldimethylammonium chloride) onto cellulosic fibers with different charge profiles was investigated. Surface carboxymethylated fibers were obtained by grafting carboxymethyl cellulose (CMC) onto the fiber surface and bulk carboxymethylated fibers were obtained by reacting the fibers with monochloroacetic acid. It was shown that nonionic interactions do not exist between cellulose and poly-DADMAC, rather electrostatic interactions govern the adsorption. Charge stoichiometry prevails under electrolyte-free conditions, whereas surface charge overcompensation occurs at higher electrolyte concentrations. It was shown that charge stoichiometry prevails if the thickness of the electric double layer kappa(-1) was larger than the mean distance between the charges on the fiber surface, as predicted by polyelectrolyte adsorption theories, taking lateral correlation effects into account. In a second set of experiments the ESCA technique served to independently calibrate the polyelectrolyte titrations for determining the surface charge of cellulosic fibers. Various molecular masses of poly-DADMAC were adsorbed to carboxymethylated fibers having different charge profiles. The adsorption of low M(w) poly-DADMAC (7.0 x 10(3)), analyzed by polyelectrolyte titration, was about 10 times higher than that of the high M(w) poly-DADMAC (9.2 x 10(5)). Despite the difference in accessibility of these two polyelectrolytes to the fiber cell wall, ESCA surface analysis showed, as expected, only slight differences between the two polyelectrolytes. This gives strong credibility to the idea that surface charge content of cellulosic fibers can be analyzed by means of adsorption of a high-molecular-mass cationic polymer, i.e., by polyelectrolyte titration. PMID:16401137

Horvath, A Elisabet; Lindström, Tom; Laine, Janne

2006-01-17

117

Potentiometric surface of the Lloyd aquifer on Long Island, New York, in January 1975  

USGS Publications Warehouse

A map showing the potentiometric surface of the Lloyd aquifer was drawn from water-level measurements made in January 1975. Altitude of the potentiometric surface ranged from more than 20 feet below mean sea level in Queens County to more than 40 feet above mean sea level in Suffolk County.

Rich, Charles A.; Prince, Keith R.; Spinello, Anthony G.

1975-01-01

118

Hydration and Lyotropic Melting of Amphiphilic Molecules: A Thermodynamic Study Using Humidity Titration Calorimetry.  

PubMed

The hydration of the lipid 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) and of the cationic detergent dodecyltrimethylammonium bromide (DTAB) has been studied by means of isothermal titration calorimetry (ITC), gravimetry, and infrared (IR) spectroscopy. During the experiments films of the amphiphiles are perfused by an inert gas of variable relative humidity. The measurement of adsorption heats using ITC represents a new adaptation of adsorption calorimetry which has been called the humidity titration technique. This method yields the partial molar enthalpy of water upon adsorption. It is found to be endothermic with respect to the molar enthalpy of water on condensation for the water molecules which interact directly with the headgroups of POPC and DTAB. Consequently, the spontaneous hydration of the amphiphiles is entropy driven in an aqueous environment. IR spectroscopy shows that hydration is accompanied by the increase in the conformational and/or motional freedom of the amphiphilic molecules upon water binding. In particular, a lyotropic chain melting transition is induced at a certain characteristic relative humidity. This event is paralleled by the adsorption of water. The corresponding exothermic adsorption heat is consumed completely (POPC) or partially (DTAB) by the hydrocarbon chains upon melting. Differential scanning calorimetry was used as an independent method to determine transition enthalpies of the amphiphiles at a definite hydration degree. Water binding onto the headgroups is discussed in terms of hydrogen bonding and polar interactions. The adsorption isotherms yield a number of approximately 2.6 tightly bound water molecules per POPC and DTAB molecule. Copyright 1999 Academic Press. PMID:10607439

Binder; Kohlstrunk; Heerklotz

1999-12-15

119

Complexometric Titrations: Competition of Complexing Agents in the Determination of Water Hardness with EDTA  

NASA Astrophysics Data System (ADS)

The competition of complexing agents for the same metal ion and the formation of colored metal-ion complexes is demonstrated with the use of an overhead projector. This demonstration can be used to emphasize both the relevance of the relative values of formation constants in the complexation of metal cations and the applicability of complexometric titrations in quantitative chemical analysis. The demonstration is based on the traditional determination of water hardness in which EDTA is used as the titrant that complexes Mg2+ and Ca2+ ions. The color change that signals the end of the titration represents the successful removal of the Mg2+ ions from the metallochromic indicator Calmagite. This removal is possible because the value of the formation constant of the [Mg(EDTA)]2- complex is about 3 orders of magnitude greater than that corresponding to the [Mg(Calmagite)]- complex. The color change from wine-red (metal-bound indicator) to blue (unbound indicator) can be seen clearly in a large classroom with the use of overhead projection.

Yappert, M. Cecilia; Dupre, Donald B.

1997-12-01

120

Modeling Precipitation and Sorption of Al, U and Co-contaminants during Titration of Acidic Sediments in Recirculation Flow-Through Experiments  

SciTech Connect

We conducted batch and recirculating column titration tests with contaminated acidic sediments with controlled CO2 in the headspace, and extended the geochemical model by Gu et al. (2003, GCA) to better understand and quantify the reactions governing trace metal fate in the subsurface. The sediment titration curve showed slow pH increase due to strong buffering by Al precipitation and CO2 uptake. Assuming precipitation of basaluminite at low saturation index (SI=-4), and decreasing cation exchange selectivity coefficient (kNa\\Al=0.3), the predictions are close to the observed pH and Al; and the model explains 1) the observed Ca, Mg, and Mn concentration decrease by cation exchange with sorbed Al, and 2) the decrease of U by surface complexation with Fe hydroxides at low pH, and precipitation as liebigite (Ca2UO2(CO3)3:10H2O) at pH>5.5. Without further adjustment geochemical parameters, the model describes reasonably well previous sediment and column titration tests without CO2 in the headspace, as well as the new large column test. The apparent inhibition of U and Ni decrease in the large column can be explained by formation of aqueous carbonate complexes and/or competition with carbonate for surface sites. These results indicated that ignoring labile solid phase Al would underestimate base requirement in titration of acidic aquifers.

Tang, Guoping [ORNL; Luo, Wensui [Institute of Urban Environment, Chinese Academy of Sciences; Brooks, Scott C [ORNL; Watson, David B [ORNL; Gu, Baohua [ORNL

2013-01-01

121

Potentiometric surface of Floridan aquifer May 1975, and change of potentiometric surface 1969 to 1975, Southwest Florida Water Management District and adjacent areas  

USGS Publications Warehouse

Maps showing the potentiometric surface of the Floridan aquifer for May 1975, and changes of potentiometric surface from 1964 to 1975 were prepared for areas in southwest Florida. Contours and color codes describe water-level changes. The larger map, scale 1:500,000, reflects the water-level changes from 1969-75. The smaller map shows the changes from January 1964 to May 1969. (Woodard-USGS)

Mills, L.R.; Laughlin, C.P.

1976-01-01

122

Covalent binding of urease on ammonium-selective potentiometric membranes.  

PubMed

As part of the development of disposable urea bioselective probes, the covalent binding of urease on ammonium-selective potentiometric membranes has been assessed. Nonactin/bis(1-butylpentyl)adipate/poly(vinylchloride) (PVC) membranes, directly applied to an internal solid contact (conductive epoxy-graphite composite), has been used as a support for covalent immobilization of urease. Two types of all-solid-state construction process have been assayed: thin layers of cellulose acetate (CA) were coated on the PVC ammonium-selective membranes (type 1) and blends of PVC and CA at various ratios were used as ammonium-selective membrane matrices (type 2). Urease was covalently attached to CA via aldehyde groups. These groups were created on the polysaccharide with sodium periodate to which the enzyme was immobilized through a spacer (hexamethylenediamine). The viability of both types of probe for the determination of ammonium ions was assessed after each step of the activation process. Results indicated that type 2 potentiometric probes are altered after the treatment with sodium periodate. Good results were obtained with type 1 probes. Their dynamic concentration range of response to urea was from 2 x 10(-5) to 0.01 M with a sensibility of 50 mV/decade. PMID:1292521

Gil, M H; Piedade, A P; Alegret, S; Alonso, J; Martinez-Fàbregas, E; Orellana, A

1992-01-01

123

Potentiometric Sensor for Real-Time Remote Surveillance of Actinides in Molten Salts  

SciTech Connect

A potentiometric sensor is being developed at the Idaho National Laboratory for real-time remote surveillance of actinides during electrorefining of spent nuclear fuel. During electrorefining, fuel in metallic form is oxidized at the anode while refined uranium metal is reduced at the cathode in a high temperature electrochemical cell containing LiCl-KCl-UCl3 electrolyte. Actinides present in the fuel chemically react with UCl3 and form stable metal chlorides that accumulate in the electrolyte. This sensor will be used for process control and safeguarding of activities in the electrorefiner by monitoring the concentrations of actinides in the electrolyte. The work presented focuses on developing a solid-state cation conducting ceramic sensor for detecting varying concentrations of trivalent actinide metal cations in eutectic LiCl-KCl molten salt. To understand the basic mechanisms for actinide sensor applications in molten salts, gadolinium was used as a surrogate for actinides. The ß?-Al2O3 was selected as the solid-state electrolyte for sensor fabrication based on cationic conductivity and other factors. In the present work Gd3+-ß?-Al2O3 was prepared by ion exchange reactions between trivalent Gd3+ from GdCl3 and K+-, Na+-, and Sr2+-ß?-Al2O3 precursors. Scanning electron microscopy (SEM) was used for characterization of Gd3+-ß?-Al2O3 samples. Microfocus X-ray Diffraction (µ-XRD) was used in conjunction with SEM energy dispersive X-ray spectroscopy (EDS) to identify phase content and elemental composition. The Gd3+-ß?-Al2O3 materials were tested for mechanical and chemical stability by exposing them to molten LiCl-KCl based salts. The effect of annealing on the exchanged material was studied to determine improvements in material integrity post ion exchange. The stability of the ß?-Al2O3 phase after annealing was verified by µ-XRD. Preliminary sensor tests with different assembly designs will also be presented.

Natalie J. Gese; Jan-Fong Jue; Brenda E. Serrano; Guy L. Fredrickson

2012-07-01

124

Determination of uranium by direct titration with dipicolinic acid  

SciTech Connect

Direct titration of uranium with dipicolinic acid, in the presence of Arsenazo I, is a simple, precise, and accurate method for uranium determination. The method is particularly attractive because it can be totally automated. Detecting the end point (color change from blue to pink) depends on the concentration range. For the Micro Method (1 to 20 ppM U in the solution titrated), the gradual color change is monitored spectrophotometrically. For the Macro Method (20 to 300 ppM), the end point is determined either visually or spectrophotometrically. The spectrophotometric end point is computed by fitting the titration curve. The relative standard deviation is +-1 to 3% for the Micro Method and +-0.3% for the Macro Method.

Baumann, E.W.

1984-07-12

125

Constant-Current Coulometric Titration of Hydrochloric Acid  

NASA Astrophysics Data System (ADS)

The titration of a strong acid with a strong base and the electrolysis of water are two classic laboratory exercises that are either performed or demonstrated in secondary school classrooms in order to introduce two important areas of chemsitry: acid-base chemistry and electrochemistry. In this experiment we have combined these two classical experiments into one complete laboratory experience. Here we report how the elctrolysis of an aqueous solution can be used to determine the concentration of hydrochloric acid in a coulometric titration.

Swim, James; Earps, Edward; Reed, Laura M.; Paul, David

1996-07-01

126

Elucidation of ionic interactions in the protic ionic liquid solutions by isothermal titration calorimetry.  

PubMed

The strong hydrogen-bonded network noted in protic ionic liquids (PILs) may lead to stronger interactions of the ionic entities of PILs with solvents (water, methanol, ethylene glycol, dimethylsulfoxide (DMSO), N,N'-dimethylformamide (DMF)) as compared with those of aprotic ionic liquids (APILs). The PILs used in this work are 1-methylimidazolium tetrafluoroborate, 2-methylpyridinium tetrafluoroborate, and N-methylpyrrolodinium tetrafluoroborate in comparison to 1-butyl-3-methylimidazolium tetrafluoroborate, which is classified as an APIL. In this work, the excess partial molar enthalpy, H(E)IL obtained from isothermal calorimetric titrations at 298.15 K is used to probe the nature of interactions of the PIL cations with solvent molecules against those present in APIL-solvent systems. This work also reports interesting flip-flopping in the thermal behavior of these PIL-solvent systems depending upon the structure of the cationic ring of a PIL. In some cases, these flip-flops are the specific fingerprints for specific PILs in a common solvent environment. The excess partial molar enthalpy at infinite dilution, H(E,?)IL, of these PILs bears a critical dependence on the solvent properties. An analysis of relative apparent molar enthalpies, ?L, of the PIL solutions by the ion interaction model of Pitzer yields important information on ionic interactions of these systems. PMID:24650134

Rai, Gitanjali; Kumar, Anil

2014-04-17

127

Map showing the potentiometric surface of the Aquia Aquifer, May 19-23, 1980  

USGS Publications Warehouse

The map is based on water level measurements made May 19-23, 1980. The well network used included 83 wells which have been screened in the Aquia aquifer (Aquia Formation of Paleocene Age). Highest levels of the potentiometric surface, 20 to 35 feet above sea level, were measured near the outcrop or subcrop of the aquifer in the topographically high areas of Anne Arundel and Prince Georges Counties. The potentiometric surface slopes to the southeast. Four separate and extensive cones of depression have developed in the potentiometric surface in the vicinities of Lexington Park, Leonardtown, Prince Frederick, and Chesapeake Beach. The cones of Leonardtown and Lexington Park seem to be merging. (USGS)

Chapelle, Frank; Drummond, Dave; Curley, Tracey

1981-01-01

128

Potentiometric surface of the Floridan Aquifer, Southwest Florida Water Management District, September 1979  

USGS Publications Warehouse

A September 1979 potentiometric-surface map of the Southwest Florida Water Management District depicts the annual high water-level period. Potentiometric levels increased 1 to 20 feet between May 1979 and September 1979, in the citrus and farming sections of southern Hillsborough, northern Hardee, southwestern Polk, northwestern DeSoto, and Manatee Counties. Water levels in these areas are widely affected by pumping for irrigation and have the greatest range in fluctuations. Water-level increases ranged from 0 to 7 feet in coastal, northern, and southern areas of the Water Management District. Generally, potentiometric levels were higher than previous September levels due to heavy rains in August and September. (USGS)

Yobbi, D.K.; Woodham, W.M.; Laughlin, Charles P.

1979-01-01

129

LABORATORY EXPERIMENT 5 PRECIPITATION TITRATION WITH SILVER NITRATE.  

E-print Network

, it is desirable to maintain the particles of silver chloride in the colloidal state. INDICATOR DichlorofluoresceinLABORATORY EXPERIMENT 5 PRECIPITATION TITRATION WITH SILVER NITRATE. The AgNO3 solution (~0.02 M surrounding the silver chloride and imparts color to the solid. To obtain a satisfactory color change

Nazarenko, Alexander

130

Titrating-Delay Matching-to-Sample in the Pigeon  

ERIC Educational Resources Information Center

The titrating-delay matching-to-sample (TDMTS) procedure offers researchers an additional behavioral task thought to capture some important features of remembering. In this procedure, the delay between sample offset and comparison onset adjusts as a function of the subject's performance. Specifically, correct matches increase the delay and…

Kangas, Brian D.; Vaidya, Manish; Branch, Marc N.

2010-01-01

131

SUBVISIBLE RETINAL LASER THERAPY Titration Algorithm and Tissue Response  

E-print Network

been used within a wide range of laser settings: from intense burns to nondamaging exposures. However and calibrate a computational model­based titration algorithm for predictable laser dosimetry ranging from by adjusting laser power to produce a barely visible lesion at 20 ms pulse duration, which is defined

Palanker, Daniel

132

Asphalt compatibility testing using the automated Heithaus titration test  

SciTech Connect

The Heithaus titration test or variations of the test have been used for over 35 years to predict compatibilities of blends of asphalts from different crude sources. Asphalt compatibility is determined from three calculated parameters that measure the state of peptization of an asphalt or asphalt blend. The parameter p{sub a} is a measure of the peptizability of the asphaltenes. The parameter p{sub a} is a measure of the peptizing power of the maltenes, and the parameter P, derived from p{sub a} and p{sub o} values, is a measure of the overall state of peptization of the asphalt or asphalt blend. In Heithaus original procedure, samples of asphalt were dissolved in toluene and titrated with n-heptane in order to initiate flocculation. The onset of flocculation was detected either by photography or by spotting a filter paper with a small amount of the titrated solution. Recently, an {open_quotes}automated{close_quotes} procedure, after Hotier and Robin, has been developed for use with asphalt. In the automated method UV-visible spectrophotometric detection measures the onset of flocculation as a peak with the percent transmittance plotted as a function of the volume of titrating solvent added to a solution of asphalt. The automated procedure has proven to be less operator dependent and much faster than the original Heithaus procedure. Results from the automated procedure show the data to be consistent with results from the original, {open_quotes}classical{close_quotes} Heithaus procedure.

Pauli, A.T. [Western Research Institute, Laramie, WY (United States)

1996-12-31

133

Determination of Acidity Constants by Gradient Flow-Injection Titration  

ERIC Educational Resources Information Center

A three-hour laboratory experiment, designed for an advanced undergraduate course in instrumental analysis that illustrates the application of the gradient chamber flow-injection titration (GCFIT) method with spectrophotometric detection to determine acidity constants is presented. The procedure involves the use of an acid-base indicator to obtain…

Conceicao, Antonio C. L.; Minas da Piedade, Manuel E.

2006-01-01

134

Characterisation of iron binding ligands in seawater by reverse titration.  

PubMed

Here we demonstrate the use of reverse titration - competitive ligand exchange-adsorptive cathodic stripping voltammetry (RT-CLE-ACSV) for the analysis of iron (Fe) binding ligands in seawater. In contrast to the forward titration, which examines excess ligands in solution, RT-CLE-ACSV examines the existing Fe-ligand complexes by increasing the concentration of added (electroactive) ligand (1-nitroso-2-naphthol) and analysis of the proportion of Fe bound to the added ligand. The data manipulation allows the accurate characterisation of ligands at equal or lower concentrations than Fe in seawater, and disregards electrochemically inert dissolved Fe such as some colloidal phases. The method is thus superior to the forward titration in environments with high Fe and low ligand concentrations or high concentrations of inert Fe. We validated the technique using the siderophore ligand ferrioxamine B, and observed a stability constant [Formula: see text] of 0.74-4.37×10(21) mol(-1), in agreement with previous results. We also successfully analysed samples from coastal waters and a deep ocean hydrothermal plume. Samples from these environments could not be analysed with confidence using the forward titration, highlighting the effectiveness of the RT-CLE-ACSV technique in waters with high concentrations of inert Fe. PMID:23427800

Hawkes, Jeffrey A; Gledhill, Martha; Connelly, Douglas P; Achterberg, Eric P

2013-03-01

135

RESEARCH Open Access Continuous positive airway pressure titration in  

E-print Network

RESEARCH Open Access Continuous positive airway pressure titration in infants with severe upper airway obstruction or bronchopulmonary dysplasia Sonia Khirani1,2 , Adriana Ramirez2,3 , Sabrina Aloui2 airway obstruction (UAO) or bronchopulmonary dysplasia (BPD). Methods: The breathing pattern

Paris-Sud XI, Université de

136

Potentiometric map of the Sparta aquifer system in Mississippi, fall, 1980  

USGS Publications Warehouse

This potentiometric map of the Sparta aquifer system is the tenth in a series of maps, prepared by the U.S. Geological Survey in cooperation with the Mississippi Department of Natural Resources, Bureau of Land and Water Resources, delineating the potentiometric surfaces of the major aquifers in Mississippi. In the outcrop area of the Sparta, the potentiometric surface is strongly affected by recharge from precipitation, by topography, and by drainage of the aquifer into streams. The potentiometric surface slopes downward generally to the west away from the area of outcrop and is strongly affected by large ground-water withdrawals in the Jackson, Yazoo City, Cleveland, Clarksdale, and Memphis areas. Historically, water levels in or near the outcrop of the Sparta have shown little or no long-term changes, but during the past 20 years, in much of the confined part of the aquifer, water levels have declined from 1 to 3 feet per year. (USGS)

Wasson, B.E.

1980-01-01

137

Potentiometric map of the Coffee Sand Aquifer in northeastern Mississippi, October and November 1978  

USGS Publications Warehouse

This potentiometric map of the Coffee Sand aquifer in northeastern Mississippi is the fourth in a series of maps, prepared by the U.S. Geological Survey in cooperation with the Mississippi Department of Natural Resources, Bureau of Land and Water Resources, delineating the potentiometric surfaces of the major aquifers in Mississippi. In the outcrop areas the potentiometric surface is strongly affected by recharge from precipitation, topography, and drainage of the aquifer by streams. The potentiometric surface slopes generally to the west away from the area of outcrop and is mildly affected by moderate ground-water withdrawals by wells in Tippah and Union County. Historically, water levels in or near the outcrop of the Coffee Sand have shown little or no long-term changes as shown by a hydrograph of one well in Alcorn County. In the downdip part of the aquifer water-level declines of 2 feet per year are common. (USGS)

Wasson, B.E.

1980-01-01

138

Galvanostatic Entrapment of Penicillinase into Polytyramine Films and its Utilization for the Potentiometric Determination of Penicillin  

PubMed Central

A sensitive and reliable potentiometric biosensor for determination of penicillin has been developed by exploiting the self-limiting growth of the non-conducting polymer, polytyramine. Optimum polytyramine-penicillinase (PTy-PNCnase) films for potentiometric detection of penicillin were accomplished with monomer solutions which contained 0.03 M tyramine, 37 U/mL penicillinase, 0.01 M KNO3, and 3 mM penicillin with an applied current density of 0.8 mA/cm2 and an electropolymerisation time of 40 seconds. The potentiometric biosensor gave a linear concentration range of 3–283 ?M for penicillin and achieved a minimum detectable concentration of 0.3 ?M. The biosensor was successfully utilized for the detection of Amoxycillin and gave an average percentage recovery of 102 ± 6%. Satisfactory recoveries of penicillin G were also achieved in milk samples with the potentiometric biosensor when concentrations are ?20 ppm. PMID:22319276

Ismail, Fatma; Adeloju, Samuel B.

2010-01-01

139

Potentiometric Detection of DNA Hybridization using Enzyme-Induced Metallization and a Silver Ion Selective Electrode  

PubMed Central

Here we report on a highly sensitive potentiometric detection of DNA hybridization. The new assay uses a low-volume solid-contact silver ion-selective electrode (Ag+-ISE) to monitor the depletion of silver ions induced by the biocatalytic reaction of the alkaline-phosphatase enzyme tag. The resultant potential change of the Ag+-ISE thus serves as the hybridization signal. Factors affecting the potentiometric hybridization response have been optimized to offer a detection limit of 50 fM (0.2 amol) DNA target. The new potentiometric assay was applied successfully to the monitoring of the 16S rRNA of E. coli pathogenic bacteria to achieve a low detection limit of 10 CFU in the 4 ?L sample. Such potentiometric transduction of biocatalytically-induced metallization processess holds great promise for monitoring various bioaffinity assays involving common enzyme tags. PMID:19908886

Wu, Jie; Chumbimuni-Torres, Karin Y.; Galik, Michal; Thammakhet, Chongdee; Haake, David A.; Wang, Joseph

2009-01-01

140

Potentiometric surface of Floridan Aquifer, Southwest Florida Water Management District and adjacent areas, May 1979  

USGS Publications Warehouse

A May 1979 potentiometric-surface map depicts the annual low water-level period. Potentiometric levels declined 4 to 21 feet between September 1978 and May 1979, in the citrus and farming sections of southern Hillsborough, northern Hardee, southwestern Polk, northwestern DeSoto, and Manatee Counties. Water levels in these areas are widely affected by pumping for irrigation and have the greatest range in fluctuations. Water-level declines ranged from 0 to 6 feet in coastal, northern, and southern areas of the Water Management District. Generally potentiometric levels were higher than previous May levels due to heavy rains in April and May. In parts of Hillsborough, Pasco, and Pinellas Counties, May 1979 potentiometric levels were 18 feet higher than those of September 1978. (USGS)

Wolansky, R.M.; Mills, L.R.; Woodham, W.M.; Laughlin, C.P.

1979-01-01

141

Aqueous complexation of trivalent lanthanide and actinide cations by N,N,N'{sub 2},N'-tetrakis(2-pyridylmethyl)ethylenediamine.  

SciTech Connect

The aqueous complexation reactions of trivalent lanthanide and actinide cations with the hexadentate ligand N,N,N{prime},N{prime}-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), have been characterized using potentiometric and spectroscopic techniques in 0.1 M NaClO{sub 4} At 25 C, the stability constant of Am(TPEN){sup 3+} is two orders of magnitude larger than that of Sm(TPEN){sup 3+}, reflecting the stronger interactions of the trivalent actinide cations with softer ligands as compared to lanthanide cations.

Beitz, J. V.; Ensor, D. D.; Jensen, M. P.; Morss, L. R.

1999-06-16

142

Propagation of error in fulvic acid titration data: a comparison of three analytical methods  

E-print Network

Propagation of error in fulvic acid titration data: a comparison of three analytical methods selective electrode and fluorescence quenching data and Waite and Morel (3) compared fulvic acid titrations

Morel, François M. M.

143

Solubility diagrams in solvent-antisolvent systems by titration calorimetry  

Microsoft Academic Search

Isothermal titration calorimetry (ITC) has been used to develop a method to construct the solid-liquid equilibrium line in\\u000a ternary systems containing the solute to precipitate and an aqueous mixed solvent. The method consists in measuring the heat\\u000a of dissolution of a solid component (the solute) during successive additions of the liquid solvent. The cumulated heat, resulting\\u000a from the successive heat

M. H. Hamedi; J.-P. E. Grolier

2007-01-01

144

Isopropyl alcohol as a solvent for free fatty acid titration  

Microsoft Academic Search

George H. Kyser of Barrow-Agee Laboratories, Inc., Cairo, Illinois, suggested the possibility of using Isopropyl Alcohol as\\u000a a substitute for Specially Denatured Alcohol, Formula No. 30, in the titration of free fatty acids in crude oil and in the\\u000a oil of cottonseed samples. This substitution would eliminate the necessity of special permits and bonds for the use of alcohol.\\u000a \\u000a Isopropyl

G. Worthen Agee

1938-01-01

145

New developments for the numerical analysis of spectrophotometric titrations  

Microsoft Academic Search

Spectrophotometric titrations are a valuable tool for the investigation of solution equilibria. Data acquisition and recent developments on methods for the analysis of the measurements are discussed in this contribution. Hard-modeling methods are based on non-linear least-squares fitting, and algorithms have been developed which can cope with the large amount of data and parameters of multiwavelength or multivariate measurements. Good

Raylene M. Dyson; Porn Jandanklang; Marcel Maeder; Caroline J. Mason; Andrew Whitson

1999-01-01

146

Scopolamine Effects Under a Titrating-Delayed-Nonmatching-to-Position Procedure  

ERIC Educational Resources Information Center

In a study of working memory, the performance of rats under titrating-delayed-nonmatching- to-position (TDNMTP) procedures was examined. Overall accuracy and the number of trials completed were inversely related to titration value, whereas the highest delay attained was directly related to titration value. When given intraperitoneally,…

Porritt, M.; Poling, A.

2008-01-01

147

Calibrationless determination of creatinine and ammonia by coulometric flow titration.  

PubMed

A precise and sensitive working microflow titration procedure was developed to determine creatinine and ammonia in urine samples. This procedure is based on enzymatic conversion of creatinine, gas diffusional membrane separation of the released ammonia into an acid acceptor stream, and coulometric titration of ammonia with hypobromite. The hypobromite is formed after the electrogeneration of bromine in an electrolyte containing 1.0 M NaBr and 0.1 M sodium borate adjusted to pH 8.5. The electrolysis current follows a triangle-programmed current-time course. An amperometric flow detector records the resulting mirror symmetrical titration curves, which show two equivalence points. The analyte concentration is calculated from the time difference between the equivalence points. For quantitative conversion of creatinine and quantitative separation of present and released ammonia no calibration is necessary to get accurate results. Both ammonia/ammonium and creatinine were determined in the range between 2 microM and 2 mM with relative standard deviations between 3.0 and 1.0% (n = 5). High recoveries were obtained for the analysis of diluted urine samples for both creatinine and ammonia. PMID:10906237

He, Z K; Fuhrmann, B; Spohn, U

2000-08-01

148

Developments in the Field of Conducting and Non-conducting Polymer Based Potentiometric Membrane Sensors for Ions Over the Past Decade  

PubMed Central

Many research studies have been conducted on the use of conjugated polymers in the construction of chemical sensors including potentiometric, conductometric and amperometric sensors or biosensors over the last decade. The induction of conductivity on conjugated polymers by treating them with suitable oxidizing agents won Heeger, MacDiarmid and Shirakawa the 2000 Nobel Prize in Chemistry. Common conjugated polymers are poly(acetylene)s, poly(pyrrole)s, poly(thiophene)s, poly(terthiophene)s, poly(aniline)s, poly(fluorine)s, poly(3-alkylthiophene)s, polytetrathiafulvalenes, poly-napthalenes, poly(p-phenylene sulfide), poly(p-phenylenevinylene)s, poly(3,4-ethylene-dioxythiophene), polyparaphenylene, polyazulene, polyparaphenylene sulfide, poly-carbazole and polydiaminonaphthalene. More than 60 sensors for inorganic cations and anions with different characteristics based on conducting polymers have been reported. There have also been reports on the application of non-conducting polymers (nCPs), i.e. PVC, in the construction of potentiometric membrane sensors for determination of more than 60 inorganic cations and anions. However, the leakage of ionophores from the membranes based on these polymers leads to relatively lower life times. In this article, we try to give an overview of Solid-Contact ISE (SCISE), Single-Piece ISE (SPISE), Conducting Polymer (CP)-Based, and also non-conducting polymer PVC-based ISEs for various ions which their difference is in the way of the polymer used with selective\\ membrane. In SCISEs and SPISEs, the plasticized PVC containing the ionophore and ionic additives govern the selectivity behavior of the electrode and the conducting polymer is responsible of ion-to-electron transducer. However, in CPISEs, the conducting polymer layer is doped with a suitable ionophore which enhances the ion selectivity of the CP while its redox response has to be suppressed.

Faridbod, Farnoush; Ganjali, Mohammad Reza; Dinarvand, Rassoul; Norouzi, Parviz

2008-01-01

149

Depression May Reduce Adherence during CPAP Titration Trial  

PubMed Central

Study Objectives: Depression is a risk factor for medication non-compliance. We aimed to identify if depression is associated with poorer adherence during home-based autotitrating continuous positive airway pressure (autoPAP) titration. Design: Mixed retrospective-observational study. Setting: Academic center. Participants: Two-hundred forty continuous positive airway pressure-naïve obstructive sleep apnea (OSA) patients. Measurements: Patients underwent approximately 1 week of home-based autoPAP titration with adherence data downloaded from the device. Electronic hospital records were reviewed in a consecutive manner for inclusion. Three areas of potential predictors were examined: (i) demographics and clinical factors, (ii) disease severity, and (iii) device-related variables. Depression and anxiety were assessed using the Hospital Anxiety and Depression Scale (HADS). Scores on the subscales were categorized as normal or clinical diagnoses of depression (? 8) and anxiety (? 11). The primary outcome variable was the mean hours of autoPAP used per night. Results: Patients were diagnosed with OSA by either attended polysomnography (n = 73, AHI 25.5[15.1-41.5]) or unattended home oximetry (n = 167, ODI3 34.0[22.4-57.4]) and had home-based autoPAP titration over 6.2 ± 1.2 nights. Mean autoPAP use was 4.5 ± 2.4 hours per night. Multiple linear regression analysis revealed that depression and lower 95th percentile pressures significantly predicted lesser hours of autoPAP use (R2 = 0.19, p < 0.001). Significantly milder OSA in those requiring lower pressures may have confounded the relationship between 95th percentile pressure and autoPAP use. Conclusion: Depression was independently associated with poorer adherence during home-based autoPAP titration. Depression may be a potential target for clinicians and future research aimed at enhancing adherence to autoPAP therapy. Citation: Law M; Naughton M; Ho S; Roebuck T; Dabscheck E. Depression may reduce adherence during CPAP titration trial. J Clin Sleep Med 2014;10(2):163-169. PMID:24532999

Law, Mandy; Naughton, Matthew; Ho, Sally; Roebuck, Teanau; Dabscheck, Eli

2014-01-01

150

Potentiometric detection and removal of copper using porphyrins  

PubMed Central

Background Copper is an essential trace element with a great importance in industry, environment and biological systems. The great advantage of ion-selective sensors in comparison with other proposed techniques is that they are measuring the free metal ion activity which is responsible for their toxicity. Porphyrins are known to be among the best ionophores in formulation of ion-selective sensors. Results A symmetrically substituted meso-porphyrin, namely: 5,10,15,20-tetrakis(4-allyloxyphenyl)porphyrin (TAPP) was used in the construction of a new copper selective-sensor and was also tested for the removal of copper from waste waters. The potentiometric response characteristics (slope and selectivity) of copper-selective electrodes based on TAPP in o-nitrophenyloctylether (o-NPOE), dioctyl phtalate (DOP) and dioctyl sebacate (DOS) plasticized with poly(vinyl chloride) membranes are compared. Conclusions The best results were obtained for the membrane plasticized with DOP. The sensor has linear response in the range 1x10-7 – 1x10-1 M with 28.4 ± 0.4 mV/decade near-Nernstian slope towards copper ions and presents good selectivity. Due to its chelating nature, the same porphyrin was also tested for the retention of copper from synthetic copper samples, showing a maximum adsorption capacity of 280 mg/g. PMID:23829792

2013-01-01

151

pH titration monitored by quantum cascade laser-based vibrational circular dichroism.  

PubMed

Vibrational circular dichroism (VCD) spectra of aqueous solutions of proline were recorded in the course of titrations from basic to acidic pH using a spectrometer equipped with a quantum cascade laser (QCL) as an infrared light source in the spectral range from 1320 to 1220 cm(-1). The pH-dependent spectra were analyzed by singular value decomposition and global fitting of a two-pK Henderson-Hasselbalch model. The analysis delivered relative fractions of the three different protonation species. Their agreement with the relative fractions obtained from performing the same analysis on pH-dependent Fourier transform infrared (FT-IR) and QCL-IR spectra validates the quantitative results from QCL-VCD. Global fitting of the pH-dependent VCD spectra of L-proline allowed for extraction of pure spectra corresponding to anionic, zwitterionic, and cationic L-proline. From a static experiment, only pure spectra of the zwitterion would be accessible in a straightforward way. A comparison to VCD spectra calculated for all three species led to assignment of vibrational modes that are characteristic for the respective protonation states. The study demonstrates the applicability of QCL-VCD both for quantitative evaluation and for qualitative interpretation of dynamic processes in aqueous solutions. PMID:24655319

Rüther, Anja; Pfeifer, Marcel; Lórenz-Fonfría, Víctor A; Lüdeke, Steffen

2014-04-10

152

The fluorenyl cation.  

PubMed

The fluorenyl cation is a textbook example for a 4? antiaromatic cation. However, contrasting results have been published on how the annelated benzene rings compensate the destabilizing effect of the 4? antiaromatic five-membered ring in its core. Whereas previous attempts to synthesize this cation in superacidic media resulted in undefined polymeric material only, we herein report that it can be generated and isolated in amorphous water ice at temperatures below 30?K by photolysis of diazofluorene. Under these conditions, the fluorenylidene is protonated by water to give the fluorenyl cation, which could be characterized spectroscopically. Its absorption in the visible-light range matches that previously obtained by ultrafast absorption spectroscopy, and furthermore, its IR spectrum could be recorded. The IR bands in amorphous ice very nicely match predictions from DFT and DFT/MM calculations, suggesting the absence of strong interactions between the cation and surrounding water molecules. PMID:25656782

Costa, Paolo; Trosien, Iris; Fernandez-Oliva, Miguel; Sanchez-Garcia, Elsa; Sander, Wolfram

2015-02-23

153

Cyclodextrin-based potentiometric sensors for midazolam and diazepam.  

PubMed

In this work the implementation of benzodiazepine ion-selective electrodes for pharmaceutical formulations control is described. The solid-contact electrodes for midazolam and diazepam are based on polymeric membranes incorporating respectively beta-cyclodextrin and (2-hydroxiproyl)-gamma-cyclodextrin as ionophores, 2-fluorophenyl 2-nitrophenyl ether as plasticizer and potassium tetrakis (p-chlorophenyl) borate as ionic additive. For conventionally shaped midazolam electrode a slope of 61.9+/-1.3 mVdec(-1), a LLLR of 5.7+/-2.7 x 10(-4)gL(-1) and pH range of 2.6-5.4 was obtained, while the corresponding values for diazepam electrodes were of 67.6+/-3.0 mVdec(-1), 4.9+/-1.5 x 10(-2)gL(-1) and 1.9-2.7 pH units, respectively. Membrane optimization was based on the molar ratio between the ionophore and additive for midazolam and on inclusion cavity of cyclodextrin for diazepam. The miniaturization of the above-described electrodes gave rise to potentiometric detectors for sequential-injection lab-on-valve system with similar characteristics albeit the useful lifetime shortened from 1 year to approximately 15 days under continuous operation. The optimized flow conditions were achieved for sample injection volumes of 20 microL propelled towards the detection cell at the flow rate of 16 microLs(-1) during 80s. Real sample analysis revealed statistical accuracy and between-days precision comparable to the general used chromatographic-based procedure. PMID:18835673

Amorim, C G; Araújo, A N; Montenegro, M C B S M; Silva, V L

2008-12-01

154

A Thermodynamic Study of Tin Oxides by Coulometric Titration  

NASA Astrophysics Data System (ADS)

The nonstoichiometries of tin oxides have been studied by coulometric titration, using solid state electrolytes (YSZ) between 694 K and 990 K. The nonstoichiometry( X) and the oxygen partial pressure ( Po 2) vary as x ? P-1/6o 2 mean 900 k. A phase Sn 3O 4 between the Sn and SnO 2 in the range of 969-732 k. The Gibbs free energy change of formation of Sn 3O 4 is given by ? GoSn 3O 4 = -1,163,960 + 417.36 T (J/mol).

Li-Zi, Yang; Zhi-Tong, Sui; Chan-Zheng, Wang

1994-12-01

155

Interaction between bisphenol A and tannic Acid: Spectroscopic titration approach  

NASA Astrophysics Data System (ADS)

The interaction between tannic acid (TA) and bisphenol A (BPA), an endocrine disruptor, was studied by absorption and fluorescence titration techniques. The binding constants and corresponding thermodynamic parameters at different temperatures (294, 296, 298, 300 and 303 K) were determined. The intrinsic fluorescence of BPA was strongly quenched by TA and the quenching mechanism is attributed to static quenching. The thermodynamic data revealed that the formation of TA-BPA complex was exothermic, entropic-driven, and spontaneous. Furthermore, hydrogen and van der Waals interactions seem to be the major driving forces for the formation of the nonfluorescent TA-BPA complex.

Omoike, Anselm; Brandt, Benjamin

2011-06-01

156

Isothermal Titration Calorimetry of Membrane Proteins – Progress and Challenges  

PubMed Central

Summary Integral membrane proteins, including G protein-coupled receptors (GPCR) and ion channels, mediate diverse biological functions that are crucial to all aspects of life. The knowledge of the molecular mechanisms, and in particular, the thermodynamic basis of the binding interactions of the extracellular ligands and intracellular effector proteins is essential to understand the workings of these remarkable nanomachines. In this review, we describe how isothermal titration calorimetry (ITC) can be effectively used to gain valuable insights into the thermodynamic signatures (enthalpy, entropy, affinity, and stoichiometry), which would be most useful for drug discovery studies, considering that more than 30% of the current drugs target membrane proteins. PMID:23747362

Rajarathnam, Krishna; Rösgen, Jörg

2013-01-01

157

Carbonic acid ionization and the stability of sodium bicarbonate and carbonate ion pairs to 200 °C - A potentiometric and spectrophotometric study  

NASA Astrophysics Data System (ADS)

Carbonic acid ionization and sodium bicarbonate and carbonate ion pair formation constants have been experimentally determined in dilute hydrothermal solutions to 200 °C. Two experimental approaches were applied, potentiometric acid-base titrations at 10-60 °C and spectrophotometric pH measurements using the pH indicators, 2-napthol and 4-nitrophenol, at 25-200 °C. At a given temperature, the first and second ionization constants of carbonic acid (K1, K2) and the ion pair formation constants for NaHCO(aq)(K) and NaCO3-(aq)(K) were simultaneously fitted to the data. Results of this study compare well with previously determined values of K1 and K2. The NaHCO(aq) and NaCO3-(aq) ion pair formation constants vary between 25 and 200 °C having values of logK=-0.18 to 0.58 and logK=1.01 to 2.21, respectively. These ion pairs are weak at low-temperatures but become increasingly important with increasing temperature under neutral to alkaline conditions in moderately dilute to concentrated NaCl solutions, with NaCO3-(aq) predominating over CO32-(aq) in ?0.1 M NaCl solution at temperatures above 100 °C. The results demonstrate that NaCl cannot be considered as an inert (non-complexing) electrolyte in aqueous carbon dioxide containing solutions at elevated temperatures.

Stefánsson, Andri; Bénézeth, Pascale; Schott, Jacques

2013-11-01

158

Cation binding by bacteriorhodopsin  

PubMed Central

We have found that extensively washed purple membrane has about 1 calcium and 3-4 magnesium ions bound per bacteriorhodopsin molecule. When these divalent cations are removed by any of a variety of means, the pigment changes its color from purple to blue (?max ? 600 nm). This blue pigment, which can be formed at near neutral pH, is probably very similar to blue species formed when the pH of a purple membrane sample is lowered to ?2. When any of a wide variety of cations are added to a blue membrane preparation, the characteristic purple color of bacteriorhodopsin returns. Divalent and trivalent cations are much more efficient than monovalent cations in restoring the purple color and are effective at a ratio approaching one cation per pigment molecule. Besides shifting the absorption spectrum, removal of the divalent cations drastically alters the photochemical cycle of bacteriorhodopsin, including abolishing the unprotonated Schiff base (M-type) intermediate. Finally, lanthanum not only displaces the divalent cations normally bound to the purple membrane but also greatly reduces both the rate of decay of the M412 intermediate and proton uptake. PMID:16593536

Chang, C.-H.; Chen, J.-G.; Govindjee, R.; Ebrey, T.

1985-01-01

159

Interaction of divalent cations with peptide fragments from Parkinson's disease genes.  

PubMed

Protected Ac-PDEKHEL-NH(2) (PK9-H) and Ac-FCGDGANDCG-NH(2) (PK9-C) peptide fragments corresponding to sequences from residues 1165 to 1171 and 1184 to 1193, respectively, in the Park9 encoded protein from Parkinson's disease gene were tested for their protonation and complex formation capabilities with Cu(II), Zn(II) and Mn(II) ions by potentiometric and UV-Vis measurements. The effects of peptide titration with the metal ions have been followed by mono- and bi-dimensional NMR spectroscopy in order to support the potentiometric results and to understand the details of metal binding. Only mononuclear complexes have been evidenced for all the checked metal ions with PK9-H peptide. Mononuclear and bis-complexes with PK9-C peptide have been evidenced with Cu(II) and Zn(II) metal ions. From the dissociation-constants and pM values obtained for the binary competition diagrams for the systems containing Cu(II), Zn(II) or Mn(II) and the two ligands, the Cu(II) ion is able to bind more efficiently than Zn(II) and Mn(II) metal ions to both ligands. PMID:23202360

Remelli, Maurizio; Peana, Massimiliano; Medici, Serenella; Delogu, Lucia Gemma; Zoroddu, Maria Antonietta

2013-05-01

160

Open-cell titration of seawater for alkalinity measurements by colorimetry using bromophenol blue combined with a non-linear least-squares method.  

PubMed

The open-cell titration of seawater was studied for alkalinity measurements by colorimetry. 1) The colorimetric pH of free hydrogen ion concentration, pH(F(ind)), was calculated from the ratio of the absorbances at 436 and 590 nm (R = (590nm)A/(436nm)A), along with the molar absorption coefficient ratios (e(1), e(2) and e(3)/e(2)) and a tentative acid dissociation constant value (pK(a(2))). 2) The perturbation of hydrogen ion was evaluated from the change in titration mass (Deltam). The total hydrogen ion concentration at m + Deltam, pH(T(at m+Deltam)), was calculated using pH(F(ind)) for a mass m and constants for sulfate (S(T)) and fluoride (F(T)). 3) The alkalinity (A(T)) was computed from the titrant mass (m + Deltam) and the corresponding pH(T(at m+Deltam)) through a non-linear least-squares approach using the pK(a(2)) value as a variable parameter. Seawater sample at 2000 m depth from the West Pacific was analyzed. The resulting A(T) (2420.92 +/- 3.35 micromol kg(-1)) was in good agreement with the A(T) measured by potentiometric electric force (2420.46 +/- 1.54 micromol kg(-1)). The resulting pK(a(2)) was 3.7037, in close proximity to that reported by King et al. (pK(a(2)) = 3.695). PMID:20543505

Okamura, Kei; Kimoto, Hideshi; Kimoto, Takashi

2010-01-01

161

Potentiometric surface of the Sparta and Memphis aquifers in eastern Arkansas, April through July 1993  

USGS Publications Warehouse

A water-level map of the Sparta and Memphis aquifers for 1993 is presented in this map report. The Sparta-Memphis aquifer, consisting of sands of Eocene age, is present in much of southern and eastern Arkansas. The potentiometric surface map and long-term hydrographs illustrate the effects of large withdrawals for industrial and public supply and, to a lesser extent, agricultural use, on water levels in the aquifer. Three cones of depression, centered in Columbia, Jefferson, and Union Counties, occur in the potentiometric surface.

Westerfield, Paul W.

1995-01-01

162

Novel potentiometric and optical silver ion-selective sensors with subnanomolar detection limits  

PubMed Central

Ten Ag+-selective ionophores have been characterized in terms of their potentiometric selectivities and complex formation constants in solvent polymeric membranes. The compounds with ?-coordination show much weaker interactions than those with thioether or thiocarbamate groups as the coordinating sites. Long-term studies with the best ionophores show that the lower detection limit of the best Ag+ sensors can be maintained in the subnanomolar range for at least one month. The best ionophores have also been characterized in fluorescent microspheres. The so far best lower detection limits of 3× 10?11M (potentiometrically) and 2 × 10?11M Ag+ (optically) are found with bridged thiacalixarenes. PMID:17723454

Szigeti, Zsófia; Malon, Adam; Vigassy, Tamás; Csokai, Viktor; Grün, Alajos; Wygladacz, Katarzyna; Ye, Nan; Xu, Chao; Chebny, Vincent J.; Bitter, István; Rathore, Rajendra; Bakker, Eric; Pretsch, Ernö

2010-01-01

163

Understanding the response behavior of potentiometric gas sensors for non-equilibrium gas mixtures  

SciTech Connect

Many applications of gas sensors require concentration measurements of reactive gases in mixtures that are out of thermodynamic equilibrium. These applications include: hydrogen and hydrocarbon fuel gas sensors operating in ambient air for explosion hazard detection, carbon monoxide detection in ambient air for health protection, combustion efficiency sensors for stoichiometry control, and nitric oxide sensors for air pollution monitoring. Many potentiometric and amperometric electrochemical sensor technologies have been developed for these applications. A class of the potentiometric sensors developed for gas mixtures are the non-Nerstian sensors. This presentation defines a categorization and theoretical analysis of three distinct electrochemical processes that can produce a non-Nernstian sensor response.

Garzon, F. H. (Fernando H.); Mukundan, R. (Rangachary); Brosha, E. L. (Eric L.)

2002-01-01

164

Potentiometric Electronic Tongues for Foodstuff and Biosample Recognition—An Overview  

PubMed Central

Potentiometric sensors are attractive tools for the fabrication of various electronic tongues that can be used in wide area of applications, ranging from foodstuff recognition to environmental monitoring and medical diagnostics. Their main advantages are the ability to modify their selectivity (including cross-sensitivity effects) and the possibility of miniaturization using appropriate construction methods for the transducer part (e.g., with the use of solid-state technology). In this overview various examples of the design, performance, and applications of potentiometric electronic tongues are presented. The results summarize recent research in the field conducted in the Department of Microbioanalytics, Warsaw University of Technology (WUT). PMID:22163870

Ciosek, Patrycja; Wróblewski, Wojciech

2011-01-01

165

Potentiometric surface of the Floridan Aquifer, Southwest Florida Water Management District and adjacent areas, September 1978  

USGS Publications Warehouse

A September 1978 potentiometric-surface map depicts the annual high water-level period of the Floridan aquifer in the Southwest Florida Management District. Potentiometric levels increased 10 to 25 feet between May 1978 and September 1978, in the citrus and farming sections of southern Hillsborough, northern Hardee, southwestern Polk and Manatee Counties. These areas are widely affected by pumping for irrigation and have the greatest fluctuations in water-levels between the low and high water-level periods. Water-level rises in coastal, northern and southern areas of the Water Management District ranged from 0 to 10 feet. (Woodard-USGS)

Wolansky, R.M.; Mills, L.R.; Woodham, W.M.; Laughlin, C.P.

1978-01-01

166

Potentiometric surface of Floridan aquifer, Southwest Florida Water Management District and adjacent areas, September 1977  

USGS Publications Warehouse

A potentiometric-surface map of the Southwest Florida Water Management District depicts the annual high water-level period. Potentiometric levels increased 15 to 30 feet between May 1977 and September 1977 in the citrus and farming sections of southeastern Hillsborough, northern Hardee, and southwestern Polk Counties. These areas are widely affected by pumpage for irrigation and have the greatest range in water-level fluctuations between the low and high water-level periods. Water-level rises in coastal, northern, and southern areas of the Water Management District ranged from 0 to 15 feet. (Woodard-USGS)

Ryder, P.D.; Mills, L.R.; Laughlin, C.P.

1978-01-01

167

In silico concurrent multisite pH titration in proteins.  

PubMed

The concurrent proton binding at multiple sites in macromolecules such as proteins and nucleic acids is an important yet challenging problem in biochemistry. We develop an efficient generalized Hamiltonian approach to attack this issue. Based on the previously developed generalized-ensemble methods, an effective potential energy is constructed which combines the contributions of all (relevant) protonation states of the molecule. The effective potential preserves important phase regions of all states and, thus, allows efficient sampling of these regions in one simulation. The need for intermediate states in alchemical free energy simulations is greatly reduced. Free energy differences between different protonation states can be determined accurately and enable one to construct the grand canonical partition function. Therefore, the complicated concurrent multisite proton titration process of protein molecules can be satisfactorily simulated. Application of this method to the simulation of the pKa of Glu49, Asp50, and C-terminus of bovine pancreatic trypsin inhibitor shows reasonably good agreement with published experimental work. This method provides an unprecedented vivid picture of how different protonation states change their relative population upon pH titration. We believe that the method will be very useful in deciphering the molecular mechanism of pH-dependent biomolecular processes in terms of a detailed atomistic description. PMID:24889139

Hu, Hao; Shen, Lin

2014-07-30

168

Complexation Effect on Redox Potential of Iron(III)-Iron(II) Couple: A Simple Potentiometric Experiment  

ERIC Educational Resources Information Center

A titration curve with multiple inflection points results when a mixture of two or more reducing agents with sufficiently different reduction potentials are titrated. In this experiment iron(II) complexes are combined into a mixture of reducing agents and are oxidized to the corresponding iron(III) complexes. As all of the complexes involve the…

Rizvi, Masood Ahmad; Syed, Raashid Maqsood; Khan, Badruddin

2011-01-01

169

Potentiometric measurement of polymer-membrane electrodes based on lanthanum  

SciTech Connect

Quantitative analysis of rare earth elements which are considered as the standard method that has a high accuracy, and detection limits achieved by the order of ppm is inductively coupled plasma atomic emission spectroscopy (ICPAES). But these tools are expensive and valuable analysis of the high cost of implementation. In this study be made and characterized selective electrode for the determination of rare earth ions is potentiometric. Membrane manufacturing techniques studied is based on immersion (liquid impregnated membrane) in PTFE 0.5 pore size. As ionophores to be used tri butyl phosphate (TBP) and bis(2-etylhexyl) hydrogen phosphate. There is no report previously that TBP used as ionophore in polymeric membrane based lanthanum. Some parameters that affect the performance of membrane electrode such as membrane composition, membrane thickness, and types of membrane materials studied in this research. Manufacturing of Ion Selective Electrodes (ISE) Lanthanum (La) by means of impregnation La membrane in TBP in kerosene solution has been done and showed performance for ISE-La. FTIR spectrum results for PTFE 0.5 pore size which impregnated in TBP and PTFE blank showed difference of spectra in the top 1257 cm{sup ?1}, 1031 cm{sup ?1} and 794.7 cm{sup ?1} for P=O stretching and stretching POC from group ?OP =O. The result showed shift wave number for P =O stretching of the cluster (?OP=O) in PTFE-TBP mixture that is at the peak of 1230 cm{sup ?1} indicated that no interaction bond between hydroxyl group of molecules with molecular clusters fosforil of TBP or R{sub 3}P = O. The membrane had stable responses in pH range between 1 and 9. Good responses were obtained using 10{sup ?3} M La(III) internal solution, which produced relatively high potential. ISE-La showed relatively good performances. The electrode had a response time of 29±4.5 second and could be use for 50 days. The linear range was between 10{sup ?5} and 10{sup ?1} M.

Saefurohman, Asep, E-mail: saefurohman.asep78@Gmail.com; Buchari,, E-mail: saefurohman.asep78@Gmail.com; Noviandri, Indra, E-mail: saefurohman.asep78@Gmail.com [Department of Chemistry, Bandung Institute of Technology (Indonesia); Syoni [Department of Metallurgy Engineering, Bandung Institute of Technology (Indonesia)

2014-03-24

170

New tobermorite cation exchangers  

Microsoft Academic Search

Tobermorite minerals, calcium silicate hydrates substituted with Al3+ and alkali, exhibit cation exchange and selectivity properties. The total cation exchange capacities of the Al3+ and alkali substituted tobermorites synthesized here range from 128 to 197 meq per 100g. These substituted tobermorites also have high selectivity for caesium and rubidium. For examples, a tobermorite synthesized from Na2SiO3, AlCl3 and CaO has

Sridhar Komarneni; Della M. Roy

1985-01-01

171

Potentiometric pH Measurements of Acidity Are Approximations, Some More Useful than Others  

ERIC Educational Resources Information Center

A recent article by McCarty and Vitz "demonstrating that it is not true that pH = -log[H+]" is examined critically. Then, the focus shifts to underlying problems with the IUPAC definition of pH. It is shown how the potentiometric method can provide "estimates" of both the IUPAC-defined hydrogen activity "and" the hydrogen ion concentration, using…

de Levie, Robert

2010-01-01

172

Detection of Catechol by Potentiometric-Flow Injection Analysis in the Presence of Interferents  

ERIC Educational Resources Information Center

This article describes an undergraduate analytical chemistry experiment developed to teach instrumental lab skills while incorporating common interferents encountered in the real-world analysis of catechol. The lab technique incorporates potentiometric-flow injection analysis on a dibenzo-18-crown-6 dual platinum electrode to detect catechol in…

Lunsford, Suzanne K.; Widera, Justyna; Zhang, Hong

2007-01-01

173

BIOSENSOR FOR DIRECT DETERMINATION OF ORGANOPHOSPHATE NERVE AGENTS. 1. POTENTIOMETRIC ENZYME ELECTRODE. (R823663)  

EPA Science Inventory

A potentiometric enzyme electrode for the direct measurement of organophosphate (OP) nerve agents was developed. The basic element of this enzyme electrode was a pH electrode modified with an immobilized organophosphorus hydrolase (OPH) layer formed by cross-linking OPH ...

174

Lead in Hair and in Red Wine by Potentiometric Stripping Analysis: The University Students' Design.  

ERIC Educational Resources Information Center

A new program for training upper secondary school chemistry teachers (SE 537 693) depends heavily on student project work. A project in which lead in hair and in red wine was examined by potentiometric stripping analysis is described and evaluated. (JN)

Josephsen, Jens

1985-01-01

175

Biosensor for direct determination of organophosphate nerve agents. 1. Potentiometric enzyme electrode  

Microsoft Academic Search

A potentiometric enzyme electrode for the direct measurement of organophosphate (OP) nerve agents was developed. The basic element of this enzyme electrode was a pH electrode modified with an immobilized organophosphorus hydrolase (OPH) layer formed by cross-linking OPH with bovine serum albumin (BSA) and glutaraldehyde. OPH catalyses the hydrolysis of organophosphorus pesticides to release protons, the concentration of which is

Priti Mulchandani; Ashok Mulchandani; Irina Kaneva; Wilfred Chen

1999-01-01

176

Cation exchange: cemical flooding experiments  

Microsoft Academic Search

Mass action equilibria equations provide a good description of cation exchange effects in laboratory floods with solutions containing sodium, calcium, and magnesium cations. These equations can aid in the design of prefloods for surfactant and polymer processes. Cation exchange in the presence of a surfactant system is found to be significantly complicated by interaction between surfactant and divalent cations. The

H. J. Hill; L. W. Lake

1977-01-01

177

Neurons limit angiogenesis by titrating VEGF in retina.  

PubMed

Vascular and nervous systems, two major networks in mammalian bodies, show a high degree of anatomical parallelism and functional crosstalk. During development, neurons guide and attract blood vessels, and consequently this parallelism is established. Here, we identified a noncanonical neurovascular interaction in eye development and disease. VEGFR2, a critical endothelial receptor for VEGF, was more abundantly expressed in retinal neurons than in endothelial cells, including endothelial tip cells. Genetic deletion of VEGFR2 in neurons caused misdirected angiogenesis toward neurons, resulting in abnormally increased vascular density around neurons. Further genetic experiments revealed that this misdirected angiogenesis was attributable to an excessive amount of VEGF protein around neurons caused by insufficient engulfment of VEGF by VEGFR2-deficient neurons. Moreover, absence of neuronal VEGFR2 caused misdirected regenerative angiogenesis in ischemic retinopathy. Thus, this study revealed neurovascular crosstalk and unprecedented cellular regulation of VEGF: retinal neurons titrate VEGF to limit neuronal vascularization. PAPERFLICK: PMID:25417109

Okabe, Keisuke; Kobayashi, Sakiko; Yamada, Toru; Kurihara, Toshihide; Tai-Nagara, Ikue; Miyamoto, Takeshi; Mukouyama, Yoh-Suke; Sato, Thomas N; Suda, Toshio; Ema, Masatsugu; Kubota, Yoshiaki

2014-10-23

178

Enzymatic activity of immobilized enzyme determined by isothermal titration calorimetry.  

PubMed

The activity of adsorbed beta-glucosidase onto spherical polyelectrolyte brushes (SPBs) is investigated by UV-Vis spectroscopy and isothermal titration calorimetry (ITC). By comparing the results of these two methods, we demonstrate that ITC is a precise method for the study of the activity of immobilized enzymes. The carrier particles used for immobilization here consist of a polystyrene core onto which poly(acrylic acid) chains are grafted. High amounts of enzyme can be immobilized in the brush layer at low ionic strength by the polyelectrolyte-mediated protein adsorption (PMPA). Analysis of the activity of beta-glucosidase was done in terms of Michaelis-Menten kinetics. Moreover, the enzymatic activity of immobilized enzyme is studied by ITC using cellobiose as substrate. All data show that ITC is a general method for the study of the activity of immobilized enzymes. PMID:18440294

Henzler, Katja; Haupt, Björn; Ballauff, Matthias

2008-07-15

179

Characteristics of aversive thresholds measured by a titration schedule1  

PubMed Central

Three variables were studied for their single and joint effects on aversive thresholds obtained by a titration schedule with electric shock as the aversive stimulus. One variable was the interval between the periodic increments in shock amplitude. Another was the size of this increment. The third was the size of the decrement produced when the subject responded. Both monkeys and humans tolerated more shock at the shorter increment-to-increment intervals than at the longer ones, confirming rat data previously obtained. Reducing the decremental step size also led to an increase in the amount of shock tolerated by monkeys. In addition, simply reducing both incremental and decremental step size without changing the interval between increments led monkeys to tolerate more shock. The attempt to explain these data was based on the changes that such manipulations might produce in the amount of avoidance behavior elicited. PMID:14055954

Weiss, Bernard; Laties, Victor G.

1963-01-01

180

Novel approaches to analysis by flow injection gradient titration.  

PubMed

Two novel procedures for flow injection gradient titration with the use of a single stock standard solution are proposed. In the multi-point single-line (MP-SL) method the calibration graph is constructed on the basis of a set of standard solutions, which are generated in a standard reservoir and subsequently injected into the titrant. According to the single-point multi-line (SP-ML) procedure the standard solution and a sample are injected into the titrant stream from four loops of different capacities, hence four calibration graphs are able to be constructed and the analytical result is calculated on the basis of a generalized slope of these graphs. Both approaches have been tested on the example of spectrophotometric acid-base titration of hydrochloric and acetic acids with using bromothymol blue and phenolphthalein as indicators, respectively, and sodium hydroxide as a titrant. Under optimized experimental conditions the analytical results of precision less than 1.8 and 2.5% (RSD) and of accuracy less than 3.0 and 5.4% (relative error (RE)) were obtained for MP-SL and SP-ML procedures, respectively, in ranges of 0.0031-0.0631 mol L(-1) for samples of hydrochloric acid and of 0.1680-1.7600 mol L(-1) for samples of acetic acid. The feasibility of both methods was illustrated by applying them to the total acidity determination in vinegar samples with precision lower than 0.5 and 2.9% (RSD) for MP-SL and SP-ML procedures, respectively. PMID:17903467

Wójtowicz, Marzena; Kozak, Joanna; Ko?cielniak, Pawe?

2007-09-26

181

Effects of Acute and Chronic Cocaine Administration on Titrating-Delay Matching-to-Sample Performance  

ERIC Educational Resources Information Center

The effects of cocaine were examined under a titrating-delay matching-to-sample procedure. In this procedure, the delay between sample stimulus offset and comparison stimuli onset adjusts as a function of the subject's performance. Specifically, matches increase the delay and mismatches decrease the delay. Titrated delay values served as the…

Kangas, Brian D.; Branch, Marc N.

2012-01-01

182

Quantification of the maleic anhydride grafted onto polypropylene by chemical and viscosimetric titrations, and FTIR spectroscopy  

Microsoft Academic Search

An acid–base titration method for an accurate and reproducible quantification of maleic anhydride grafted onto polyolefins is proposed. The use of an organic base (tetra-butylammonium hydroxide) enhances the base solubility in organic solvents and prevents phenomena like coarcervation. The titration goes on until the visual endpoint of a coloured indicator, corresponding to the neutralisation of the grafted functions. Bromothymol blue

M. Sclavons; P. Franquinet; V. Carlier; G. Verfaillie; I. Fallais; R. Legras; M. Laurent; F. C. Thyrion

2000-01-01

183

A Laser-Pointer-Based Spectrometer for Endpoint Detection of EDTA Titrations  

ERIC Educational Resources Information Center

A laser spectrometer for the ethylenediaminetetra-acetic acid (EDTA) titration of magnesium or calcium ions that is designed around a handheld laser pointer as the source and a photoresistor as the detector is developed. Findings show that the use of the spectrometer reduces the degree of uncertainty and error in one part of the EDTA titrations,…

Dahm, Christopher E.; Hall, James W.; Mattioni, Brian E.

2004-01-01

184

Dose titration of BAF312 attenuates the initial heart rate reducing effect in healthy subjects  

PubMed Central

Aim Previous studies have shown transient decreases in heart rate (HR) following administration of sphingosine 1?phosphate (S1P) receptor modulators including BAF312. This study was conducted to determine whether dose titration of BAF312 reduces or eliminates these effects. Methods Fifty?six healthy subjects were randomized 1:1:1:1 to receive BAF312 in one of two dose titration (DT) regimens (DT1 and DT2: 0.25–10?mg over 9–10?days), no titration (10?mg starting dose) or placebo. Pharmacodynamic and pharmacokinetic parameters were assessed. Results Neither DT1 nor DT2 resulted in clinically significant bradycardia or atrioventricular conduction effects. Both titration regimens showed a favourable difference on each of days 1–12 vs. the non?titration regimen on day 1 for HR effects (P < 0.0001). On day 1, the geometric mean ratio of the fraction from the previous day in minimum daily HR between DT1 and non?titration was 1.18 (95% confidence interval [CI] 1.13, 1.23) and 1.14 (95% CI 1.09, 1.18) for DT2 (both P < 0.05) with significant differences noted through to day 12. Non?titration HRs showed considerable separation from placebo throughout the study. There was no statistically significant reduction in HR vs. placebo on day?1 in either titration regimen. On days 3–7 subjects in DT1 and DT2 experienced minor reductions in HR vs. placebo (approximately 5?beats?min?1; P ? 0.0001). From days 9–12, HRs in both titration regimens were comparable with placebo. Conclusion Both titration regimens effectively attenuated the initial bradyarrhythmia observed on day 1 of treatment with BAF312 10?mg. PMID:22845008

Legangneux, Eric; Gardin, Anne; Johns, Donald

2013-01-01

185

Probing lectin-mucin interactions by isothermal titration microcalorimetry.  

PubMed

Isothermal titration microcalorimetry (ITC) can directly determine the thermodynamic binding parameters of biological molecules including affinity constant, binding stoichiometry, and heat of binding (enthalpy) and indirectly the entropy and free energy of binding. ITC has been extensively used to study the binding of lectins to mono- and oligosaccharides, but limited applications to lectin-glycoprotein interactions. Inherent experimental challenges to ITC include sample precipitation during the experiment and relative high amount of sample required, but careful design of experiments can minimize these problems and allow valuable information to be obtained. For example, the thermodynamics of binding of lectins to multivalent globular and linear glycoproteins (mucins) have been described. The results are consistent with a dynamic binding mechanism in which lectins bind and jump from carbohydrate to carbohydrate epitope in these molecules leading to increased affinity. Importantly, the mechanism of binding of lectins to mucins appears similar to that for a variety of protein ligands binding to DNA. Recent results also show that high affinity lectin-mucin cross-linking interactions are driven by favorable entropy of binding that is associated with the bind and jump mechanism. The results suggest that the binding of ligands to biopolymers, in general, may involve a common mechanism that involves enhanced entropic effects that facilitate binding interactions. PMID:25253134

Dam, Tarun K; Brewer, C Fred

2015-01-01

186

Characterization of membrane protein interactions by isothermal titration calorimetry.  

PubMed

Understanding the structure, folding, and interaction of membrane proteins requires experimental tools to quantify the association of transmembrane (TM) helices. Here, we introduce isothermal titration calorimetry (ITC) to measure integrin ?IIb?3 TM complex affinity, to study the consequences of helix-helix preorientation in lipid bilayers, and to examine protein-induced lipid reorganization. Phospholipid bicelles served as membrane mimics. The association of ?IIb?3 proceeded with a free energy change of -4.61±0.04kcal/mol at bicelle conditions where the sampling of random helix-helix orientations leads to complex formation. At bicelle conditions that approach a true bilayer structure in effect, an entropy saving of >1kcal/mol was obtained from helix-helix preorientation. The magnitudes of enthalpy and entropy changes increased distinctly with bicelle dimensions, indicating long-range changes in bicelle lipid properties upon ?IIb?3 TM association. NMR spectroscopy confirmed ITC affinity measurements and revealed ?IIb?3 association and dissociation rates of 4500±100s(-1) and 2.1±0.1s(-1), respectively. Thus, ITC is able to provide comprehensive insight into the interaction of membrane proteins. PMID:25178257

Situ, Alan J; Schmidt, Thomas; Mazumder, Parichita; Ulmer, Tobias S

2014-10-23

187

Potentiometric dyes: new modalities for optical imaging of membrane potential  

NASA Astrophysics Data System (ADS)

Voltage sensitive dyes permit the measurement of biomembrane electrical activity where microelectrode measurements are unsuitable or inadequate. This laboratory has developed 2 class of such dyes as well as some new optical methods for mapping membrane potential in single cells. One class of compounds consists of amphiphilic membrane staining dyes containing a putative electrochromic chromophore aligned perpendicular to the membrane/aqueous interface. We have used these dyes to map the membrane potential along the surface of single cells with high resolution dual wavelength ratiometric imaging microscopy techniques. We have found intrinsic regional variations in the electrical properties of cell membranes. Adding chirality produces compounds that display remarkable efficiencies for second harmonic generation. Further, the second harmonic signal can be generated from a dye-stained membrane and is modulatable by changing the membrane voltage. This can form the basis for measurements of membrane electrophysiology at high 3D resolution with infrared light. A second class of dyes are membrane-permeant cations which act as Nernstian indicators. We have developed calibration methods which allow the use of these compounds to quantitate the membrane potential of individual mitochondria from confocal or widefield images of living cells.

Loew, Leslie M.

1996-05-01

188

Geostatistical analysis of potentiometric data in the Pennsylvanian aquifer of the Palo Duro Basin, Texas  

SciTech Connect

This report details a geostatistical analysis of potentiometric data from the Pennsylvanian aquifer in the Palo Duro Basin, Texas. Such an analysis is a part of an overall uncertainty analysis for a high-level waste repository in salt. Both an expected potentiometric surface and the associated standard error surface are produced. The Pennsylvanian data are found to be well explained by a linear trend with a superimposed spherical semivariogram. A cross-validation of the analysis confirms this. In addition, the cross-validation provides a point-by-point check to test for possible anomalous data. The analysis is restricted to that portion of the Pennsylvanian aquifer that lies to the southwest of the Amarillo Uplift. The Pennsylvanian is absent is some areas across the uplift and data to the northeast were not used in this analysis. The surfaces produced in that analysis are included for comparison. 9 refs., 15 figs.

Harper, W.V.; Basinger, K.L.; Furr, J.M.

1988-01-01

189

Potentiometric strip cell based on carbon nanotubes as transducer layer: toward low-cost decentralized measurements.  

PubMed

In this study, we developed a potentiometric planar strip cell based on single-walled carbon nanotubes that aims to exploit the attributes of solid-contact ion-selective electrodes for decentralized measurements. That is, the ion-selective and reference electrodes have been simultaneously miniaturized onto a plastic planar substrate by screen-printing and drop-casting techniques, obtaining disposable strip cells with satisfactory performance characteristics (i.e., the sensitivity is 57.4 ± 1.3 mV/dec, the response time is ?30 s within the linear range from log a(K+) = -5 to -2, and the limit of detection is -6.5), no need of maintenance during long dry storage, quick signal stabilization, and light insensitivity in short-term measurements. We also show how the new potentiometric strip cell makes it possible to perform decentralized and rapid determinations of ions in real samples, such as saliva or beverages. PMID:21961835

Rius-Ruiz, F Xavier; Crespo, Gastón A; Bejarano-Nosas, Diego; Blondeau, Pascal; Riu, Jordi; Rius, F Xavier

2011-11-15

190

Maltodextrins as new chiral selectors in the design of potentiometric, enantioselective membrane electrodes.  

PubMed

Maltodextrins (dextrose equivalent (DE) 4.0-7.0, 13.0-17.0, and 16.5-19.5) are proposed as novel chiral selectors for the construction of potentiometric, enantioselective membrane electrodes. The potentiometric, enantioselective membrane electrodes can be used reliably for the assay of S-captopril as raw material and in pharmaceutical formulations such as Novocaptopril tablets, by use of direct potentiometry. The best response was obtained when maltodextrin with higher DE was used for construction of the electrode. The best enantioselectivity and time-stability was achieved for the lower DE maltodextrin. L-proline was found to be the main interferent for all the proposed electrodes. The surface of the electrodes can be regenerated by simply polishing; this furnishes a fresh surface ready for use in a new assay. PMID:11393233

Stefan, R I; van Staden, J F; Aboul-Enein, H Y

2001-05-01

191

Potentiometric measurements in sequential injection analysis lab-on-valve (SIA-LOV) flow-system.  

PubMed

Advantages of using sequential injection analysis lab-on-valve (SIA-LOV) in potentiometric measurements are studied with Ca(2+) sensitive solid-contact ion-selective electrodes (SC-ISE) and pH electrode based on polyaniline (PANI). Experiments show that Ca(2+)-SC-ISE requires a stopped flow mode to be used in order to get longer equilibration time. On the other hand, PANI based pH electrode gives better results under flow conditions. SIA-LOV was found to be a flexible solution handling system for potentiometric measurements. The technique gives a possibility to fine-tune the calibration range or even recondition the electrode before every measurement without losing in linear range of calibration. PMID:19071283

Kikas, Timo; Ivaska, Ari

2007-01-15

192

Chiral salen Mn(III) complex-based enantioselective potentiometric sensor for L-mandelic acid.  

PubMed

A new enantioselective potentiometric sensor containing chiral salen Mn(III) as the chiral selector was designed for the assay of L-mandelic acid (L-MA). Optimized membrane electrodes displayed linear dynamic range from 1x10(-5) to 1x10(-1) mol L(-1) with a detection limit of 7.2x10(-6) mol L(-1) and a Nernstian response of -58.1+/-0.5 mV decade(-1) towards L-MA within pH range 7.0-10.2. The potentiometric enantioselectivity coefficient (logK(L,D)(Pot)) of this sensor was -4.0, indicating that the chiral salen Mn(III) complex-based electrode exhibited fairly good discrimination toward L-MA over counter isomer D-MA. The mechanism of chiral recognition for L-MA is discussed by using HF/STO-3G calculation method simulation. PMID:19808117

Xu, Lan; Yang, Yuanyuan; Wang, Yaqiong; Gao, Jiuzhi

2009-10-27

193

The titration of the active centers of cellobiohydrolase from Trichoderma reesei.  

PubMed

A novel approach has been developed for the titration of enzyme active centers and for the determination of the molecular activity of enzymes. It is based on the simultaneous use of a nonspecific chromogenic substrate and a specific ligand (a substrate or an inhibitor), the latter being tightly bound with the enzyme's active center. The approach is demonstrated using the titration (that is, the determination of the molar concentration of the enzyme active centers) of purified cellobiohydrolase I (CBH I) (EC 3.2.1.91) of the fungus Trichoderma reesei. p-Nitrophenyl-beta-D-lactoside was used as a reference substrate (Km = 0.5 mM), and cellobiose and CM-cellulose as specific ligands. The molecular weight of CBH I as it was determined by the titration with cellobiose was 42,000 +/- 3,000. The inhibition constant by cellobiose was (6 +/- 1) X 10(-6) M. The value of the catalytic constant for the hydrolysis of p-nitrophenyl-beta-D-lactoside calculated from the titration data was equal to 0.063 s-1. CM-cellulose turned out to be more efficient titration agent for cellobiohydrolase than cellobiose, and might be used for the titration of the enzyme in concentrations of the latter of 0.008-0.02 mg/ml. The titration data showed that the inhibition constant of CM-cellulose toward CBH I was equal to (1.0 +/- 0.2) X 10(-7) M. PMID:3766948

Rabinowitch, M L; Klyosov, A A; Melnick, M S

1986-08-01

194

Cation-cation interaction in crystalline actinide compounds  

NASA Astrophysics Data System (ADS)

The published data on the structures and properties of crystalline actinide compounds having mutually coordinated AnO2+ or AnO22+ cations as structural elements are surveyed. This cation-cation interaction is an important structure-forming factor for many crystalline compounds of Np(V) and U(VI). It strongly affects their UV-Vis and IR spectra as well as other properties. Differences and similarities between the cation-cation interactions of actinide ions in solutions and crystals are discussed.

Krot, Nikolai N.; Grigoriev, Mikhail S.

2004-01-01

195

Dynamic behavior of potentiometric ammonia-sensing probes in samples of high osmolarity  

Microsoft Academic Search

Summary. Results are presented for potentiometric ammonia gas-sensors which show that the response times increase significantly with age of the sensor when ammonium picrate is used as internal electrolyte and the samples have greater osmolarities than the internal electrolyte solution. A build-up of ammonium picrate crystals on the inner side of the gas-permeable membrane is responsible for this increase in

Mark A. Arnold; Garry A. Rechnitz

1984-01-01

196

Preliminary investigations on a new disposable potentiometric biosensor for uric acid  

Microsoft Academic Search

In this paper, uricase, catalase, and electron mediator were coimmobilized on the surface of the tin oxide (SnO2)\\/indium tin oxide (ITO) glass, to develop a disposable potentiometric uric acid biosensor. The SnO2 \\/ ITO glass was employed as a pH sensor, fabricated by sputtering SnO2 thin films on the ITO glass. 3-Glycidyloxypropyltrimethoxysilane (GPTS) was utilized to immobilize uricase, catalase and

Cheng Wei Liao; Jung Chuan Chou; Tai Ping Sun; Shen Kan Hsiung; Jui Hsiang Hsieh

2006-01-01

197

Strip bioelectrochemical cell for potentiometric measurements fabricated by screen-printing  

Microsoft Academic Search

Miniaturized, planar bioelectrochemical cell dedicated for potentiometric detection of urea manufactured in integrated strip format has been developed. The enzyme electrode and the reference electrode, both based on ruthenium dioxide were fabricated only by means of screen-printing. The application of the thick-film technology results in highly reproducible and cost-effective manufacturing procedure, easily adapted to large-scale production. The developed system of

?ukasz Tymecki; El?bieta Zwierkowska; Robert Koncki

2005-01-01

198

Simulated changes in potentiometric levels resulting from groundwater development for phosphate mines, west-central Florida  

USGS Publications Warehouse

A digital model of two-dimensional groundwater flow was used to predict changes in the potentiometric surface of the Floridan aquifer resulting from groundwater development for proposed and existing phosphate mines during 1976-2000. The modeled area covers 15,379 km2 in west-central Florida. In 1975, groundwater withdrawn from the Floridan aquifer for irrigation, phosphate mines, other industries and municipal supplies averaged about 28,500 l/s. Withdrawals for phosphate mines are expected to shift from Polk County to adjacent counties to the south and west, and to decline from about 7,620 l/s in 1975 to about 7,060 l/s in 2000. The model was calibrated under steady-state and transient conditions. Input parameters included aquifer transmissivity and storage coefficient; thickness, vertical hydraulic conductivity, and storage coefficient of the upper confining bed; altitudes of the water table and potentiometric surface; and groundwater withdrawals. Simulation of November 1976 to October 2000, using projected combined pumping rates for existing and proposed phosphate mines, resulted in a rise in the potentiometric surface of about 6 m in Polk County, and a decline of about 4 m in parts of Manatee and Hardee counties. ?? 1979.

Wilson, W.E.; Gerhart, J.M.

1979-01-01

199

Potentiometric and spectrophotometric study of the stability of magnesium carbonate and bicarbonate ion pairs to 150 °C and aqueous inorganic carbon speciation and magnesite solubility  

NASA Astrophysics Data System (ADS)

The formation constants of magnesium bicarbonate and carbonate ion pairs have been experimentally determined in dilute hydrothermal solutions to 150 °C. Two experimental approaches were applied, potentiometric acid-base titrations at 10-60 °C and spectrophotometric pH measurements using two pH indicators, 2-naphthol and 4-nitrophenol, at 25 and 80-150 °C. At a given temperature, the first and second ionization constants of carbonic acid (K1, K2) and the ion pair formation constants for MgHCO3+(aq) (KMgHCO3+) and MgCO3(aq) (KMgCO3) were simultaneously fitted to the data. Results of this study compare well with previously determined values of K1 and K2. The formation constants of MgHCO3+(aq) and MgCO3(aq) ion pairs increased significantly with increasing temperature, with values of logKMgHCO3+ = 1.14 and 1.75 and of logKMgCO3 = 2.86 and 3.48 at 10 °C and 100 °C, respectively. These ion pairs are important aqueous species under neutral to alkaline conditions in moderately dilute to concentrated Mg-containing solutions, with MgCO3(aq) predominating over CO32-(aq) in solutions at pH >8. The predominance of magnesium carbonate over carbonate is dependent on the concentration of dissolved magnesium and the ratio of magnesium over carbonate. With increasing temperature and at alkaline pH, brucite solubility further reduced the magnesium concentration to levels below 1 mmol kg-1, thus limiting availability of Mg2+(aq) for magnesite precipitation.

Stefánsson, Andri; Bénézeth, Pascale; Schott, Jacques

2014-08-01

200

Isothermal titration calorimetry in nanoliter droplets with subsecond time constants.  

PubMed

We reduced the reaction volume in microfabricated suspended-membrane titration calorimeters to nanoliter droplets and improved the sensitivities to below a nanowatt with time constants of around 100 ms. The device performance was characterized using exothermic acid-base neutralizations and a detailed numerical model. The finite element based numerical model allowed us to determine the sensitivities within 1% and the temporal dynamics of the temperature rise in neutralization reactions as a function of droplet size. The model was used to determine the optimum calorimeter design (membrane size and thickness, junction area, and thermopile thickness) and sensitivities for sample volumes of 1 nL for silicon nitride and polymer membranes. We obtained a maximum sensitivity of 153 pW/(Hz)(1/2) for a 1 ?m SiN membrane and 79 pW/(Hz)(1/2) for a 1 ?m polymer membrane. The time constant of the calorimeter system was determined experimentally using a pulsed laser to increase the temperature of nanoliter sample volumes. For a 2.5 nanoliter sample volume, we experimentally determined a noise equivalent power of 500 pW/(Hz)(1/2) and a 1/e time constant of 110 ms for a modified commercially available infrared sensor with a thin-film thermopile. Furthermore, we demonstrated detection of 1.4 nJ reaction energies from injection of 25 pL of 1 mM HCl into a 2.5 nL droplet of 1 mM NaOH. PMID:21913688

Lubbers, Brad; Baudenbacher, Franz

2011-10-15

201

Circular dichroism-inhibitor titrations of arsanilazotyrosine-248 carboxypeptidase A.  

PubMed

Coupling of carboxypeptidase with diazotized arsanilic acid specifically modifies a single tyrosyl residue. Yet, owing to the fact that the resultant azoTyr-248 can form an intramolecular chelate with zinc, two different circular dichroism probes result: azoTyr-248 itself and the azoTyr-248-Zn chelate. Both are environmentally sensitive and, characteristically, each can signal the same or different perturbations, as is apparent from circular dichroic spectra. This dual probe function greatly magnifies the scope of these chromophores in mapping the topography of the active center with respect to sites of interaction of inhibitors (or substrates). Titration of the azoenzyme with a series of synthetic, competitive inhibitors, e.g., L-benzylsuccinate, L-phenyllactate, and L-Phe, and with the pseudosubstrate, Gly-L-Tyr, in turn generates characteristic circular dichroic spectra. Their analysis yields a single binding constant for each of these agents, one molecule of each binding to the active center. Mixed inhibitions, as seen with beta-phenylpropionate and phenylacetate, resolved previously into competitive and noncompetitive components, are characterized by different spectral effects. Two molecules of these agents bind to the enzyme, consistent with both thermodynamic and enzymatic studies. The interactions leading to competitive and noncompetitive inhibition, respectively, can be recognized and assigned, based on the manner in which the extrema at 340 and 420 nm, reflecting azoTyr-248, and the negative 510-nm circular dichroism band, typical of its chelate with zinc, are affected and on the pH dependence of spectral and kinetic data. Certai4 noncompetitive inhibitors and modifiers induce yet other spectral features. Each probe is very sensitive to changes in its particular active center environment, though both can be relatively insensitive to inhibitors interacting at a distance from the active center. PMID:1247518

Johansen, J T; Klyosov, A A; Vallee, B L

1976-01-27

202

Cation radicals of xanthophylls  

Microsoft Academic Search

Carotenes and xanthophylls are well known to act as electron donors in redox processes. This ability is thought to be associated\\u000a with the inhibition of oxidative reactions in reaction centers and light-harvesting pigment–protein complexes of photosystem\\u000a II (PSII). In this work, cation radicals of neoxanthin, violaxanthin, lutein, zeaxanthin, ?-cryptoxanthin, ?-carotene, and\\u000a lycopene were generated in solution using ferric chloride as

Mary Grace I. Galinato; Dariusz Niedzwiedzki; Cailin Deal; Robert R. Birge; Harry A. Frank

2007-01-01

203

Binding of cationic surfactants to a thermo-sensitive copolymer below and above its cloud point.  

PubMed

The binding interactions between cationic surfactants and a statistical thermo-sensitive copolymer based on oligo(ethylene glycol) methacrylates were studied by isothermal titration calorimetry (ITC), surfactant selective electrode (SSE) and dynamic light scattering (DLS). Strong binding interactions were observed between this copolymer and cationic surfactants. The binding is driven by the hydrophobic effect, occurring on the hydrophobic backbone instead of the ethylene-glycol side chains. The surfactant saturation concentration C2 depended on the polymer concentration, but was not affected by temperature. Three types of cationic alkyltrimethylammonium bromide surfactants (RTAB with R equal to C12, C14, and C16), namely, dodecyltrimethylammonium bromide (DoTAB), tetradecyltrimethylammonium bromide (TTAB), and cetyltrimethylammonium bromide (CTAB), were examined, and the results confirmed that the binding affinity followed the sequence: CTAB>TTAB>DoTAB. PMID:24144369

Peng, Baoliang; Han, Xia; Liu, Honglai; Tam, Kam C

2013-12-15

204

40 CFR Appendix A to Part 425 - Potassium Ferricyanide Titration Method  

...Sulfite interferes and must be precipitated with barium chloride. Thiosulfate is not titrated under the...stoppered container. 4. Preparation of 0.05M barium chloride solution: Dissolve 12-13 g. barium chloride dihydrate in 1 liter of...

2014-07-01

205

Amperometric titration of mercury with a stationary platinum electrode in stirred solutions.  

PubMed

Amperometric titration of mercury (in the range of 0-4 to 3.5 mg) has been carried out with 2-mercaptobenzoxazole with a stationary electrode in stirred solution in a sodium acetate-acetic acid medium. PMID:18959909

Bera, B C; Chakrabartty, M M; Bag, S P; Mallik, K L

1966-03-01

206

telomeric DNA (17). It is possible that the extra telomeric sequences in ALT cells are titrating  

E-print Network

telomeric DNA (17). It is possible that the extra telomeric sequences in ALT cells are titrating locus (the clark kent alleles) are associated with dense hypermethylation at noncanonical cytosines (Cp

Jacobsen, Steve

207

Investigation of moisture and acids in nonaqueous mixtures by means of high frequency titration methods  

E-print Network

in kOeten?, ~ ? ~ ? i ? ~ ~ ??? 80 V? Titration of Benaonoaolfonio 405d in kootono? ~ ??? ~ ? ~ 83 I VX, Titration of o?VhthaXie kog in keatone?, ?, ???, ?, ? 85 VXX? Titration of Water in koetono i ~ ??? ~ ~ i ?? q ~ ~ ?? 8V vlxI, Titrat1om of R..., T?RLTIOI Ot lEN@SR@L@lHXO 40?D Sf kgZNSE 5?00 RiOg003@8? '85?O WO?5 VX?5' '5. so '1?lo V?50 W9?0 , 54 5 ?55?O W8?O '5l?O 8?00 I 8?50 54?O &5?0 aa, s 0864 ~ iO ee. . ~eae~ani0. 'aorta 0. 0845 a f l Oo00 loCO 9o00 5o 00 4o00...

Turner, Vester Lamar

2012-06-07

208

Journal of Electroanalytical Chemistry 512 (2001) 8391 Faradaic impedance titration of pure 3-mercaptopropionic acid  

E-print Network

Journal of Electroanalytical Chemistry 512 (2001) 83­91 Faradaic impedance titration of pure 3-mercaptopropionic acid and ethanethiol mixed monolayers on gold Kyuwon Kim, Juhyoun Kwak * Department of Chemistry

Kwak, Juhyoun

209

Expenditures Associated with Dose Titration At Initiation of Therapy in Patients With Major Depressive Disorder  

PubMed Central

Objective. Although selective serotonin reuptake inhibitors (SSRIs) are considered cost-effective medications for patients with major depressive disorder (MDD), significant dosage adjustments are often necessary when treatment is initiated. Our study was conducted to examine whether dose titration for SSRIs at initiation of therapy was associated with a greater use of health care resources and higher costs. Study Design. A retrospective database analysis was conducted. Methods. A nationally representative cohort of individuals with MDD was identified in a large managed care claims database between January 1, 2004, and December 31, 2006. A study-specific titration algorithm was used to identify patients who underwent dose titration, compared with those who did not, within the first eight weeks of initiating SSRI therapy. We calculated propensity scores and identified a 1:1 matched cohort of titration versus non-titration patients. We used univariate and multivariate statistical tests to compare the mean number of therapeutic days, health care service utilization, and expenditures between the two groups during the first eight weeks (56 days) of treatment and six months (180 days) after treatment began. Results. Over the first eight weeks, the titration cohort had a 32% decrease in the adjusted mean number of therapeutic days (38 vs. 56, respectively; P < 0.001), a 50% increase in depression-related outpatient visits (1.8 vs. 1.2; P < 0.001), a 38% increase in depression-related outpatient costs ($137 vs. $81; P ? 0.001), an increase in antidepressant pharmacy costs ($139 vs. $61; P < 0.001), and a 64% increase in psychiatric visits (0.69 vs. 0.42; P = 0.001), compared with the matched non-titration cohort. These differences were consistent among individual SSRI groups as well as during the six-month period. Conclusion. Patients undergoing dose titration of SSRIs at the beginning of therapy consumed more medical resources and spent more days receiving a subtherapeutic dose than a comparable control group without dose titration. Differences in the utilization of resources were consistent with increased patient monitoring in the titration group; however, the added benefit of titration could not be assessed with this database. PMID:20844695

Camacho, Fabian; Kong, Meg C.; Sheehan, David V.; Balkrishnan, Rajesh

2010-01-01

210

Isothermal titration calorimetric analysis on solubilization of an octane oil-in-water emulsion in surfactant micelles and surfactant-anionic polymer complexes.  

PubMed

Polymers may alter the ability of surfactant micelles to solubilize hydrophobic molecules depending on surfactant-polymer interactions. In this study, isothermal titration calorimetry (ITC) was used to investigate the solubilization thermodynamics of an octane oil-in-water emulsion in anionic sodium dodecylsulphate (SDS), nonionic polyoxyethylene sorbitan monooleate (Tween 80), cationic cetyltrimethylammonium bromide (CTAB) surfactant micelles and respective complexes formed by these micelles and an anionic polymer (carboxymethyl cellulose). Results indicated that the oil solubilization in single ionic micelles was endothermic, while in nonionic micelles or mixed ionic/nonionic micelles it was exothermic. The addition of carboxymethyl cellulose did not influence the solubilization behavior in these micelles, but affected the solubilization capacities of these systems. The solubilization capacity of cationic micelles or mixed cationic/nonionic micelles was enhanced while that of nonionic or anionic micelles was decreased. Based on the phase separation model, a molecular pathway mechanism driven by enthalpy was proposed for octane solubilization in surfactant micelles and surfactant-polymer complexes. PMID:25454419

Zhang, Hui; Zeeb, Benjamin; Salminen, Hanna; Weiss, Jochen

2015-01-15

211

Conductometric and pHmetric titrations of Extremely Diluted Solutions using HCl solutions as titrant  

Microsoft Academic Search

We carried out conductometric titrations of Extremely Diluted Solutions (EDS), obtained through an iterative process of successive dilutions and agitations. The aim of our investigations was to gain information on whether the agitation\\/dilution processes could produce non-equilibrium changes in the supramolecular structure of water and aqueous solutions. The titrations were performed by adding HCl solutions at concentrations between 1·10?4 and

C. M. Cacace; L. Elia; V. Elia; E. Napoli; M. Niccoli

2009-01-01

212

Revisiting titration procedures for the determination of exchangeable acidity and exchangeable aluminum in soils  

Microsoft Academic Search

The use of 1 mol L ammonium chloride (NH4Cl) or ammonium nitrate (NH4NO3) solutions as alternative soil extractants were evaluated for the determination of the exchangeable acidity and exchangeable aluminum (Al) in twelve soil samples by the traditional titration\\/back?titration method. The exchangeable Al results were compared with those obtained by inductively coupled plasma emission spectrometry (ICP?AES) measurements while the exchangeable

Aline Renée Coscione; João Carlos de Andrade; Bernardo van Raij

1998-01-01

213

High school students' understanding of titrations and related acid- base phenomena  

Microsoft Academic Search

Acid-base titrations are common laboratory activities carried out in high school chemistry courses. Using a series of qualitative and computer-based tasks, this study examined sixteen American students' understanding of titrations. The findings indicated that students had considerable difficulty with acid-base chemistry, were unable to describe accurately acid-base concepts, such as pH, neutralization, strength, and the theoretical descriptions of acids and

Keith Sheppard

214

Report of a patient chewing fentanyl patches who was titrated onto methadone  

PubMed Central

This case report discusses the clinical presentation and management of a patient presenting to substance misuse services reporting chewing fentanyl patches in addition to wearing them transdermally. The patient was successfully titrated onto methadone 30 mg. Only one previously reported case of an individual chewing fentanyl patches was found in the literature; no case reports were found where treatment involved titrating the patient onto methadone. The pharmacology and illicit use of fentanyl are also considered. PMID:22114625

Dale, Eric; Ashby, Fleur; Seelam, Kalyan

2009-01-01

215

Unusual properties of crocodilian ovomacroglobulin shown in its methylamine treatment and sulfhydryl titration  

SciTech Connect

The inhibitory activity of chicken and crocodilian ovomacroglobulins against trypsin was measured before and after their incubation with methylamine. The result for crocodilian ovomacroglobulin showed that methylamine treatment destroyed half of its activity, in unique contrast to human alpha 2-macroglobulin and chicken ovomacroglobulin for which methylamine either destroys the inhibitory activity of the former completely or does not affect that of the latter at all. Free sulfhydryl groups of chicken and crocodilian ovomacroglobulins were titrated with 5,5'-dithiobis(2-nitrobenzoic acid) before and after incubation with trypsin. Prior to the incubation with trypsin the chicken and crocodilian proteins respectively had 0 and 1 titratable sulfhydryl per molecule of Mr 720,000. After treatment with trypsin the crocodilian protein had 3.5-4 titratable sulfhydryls, whereas there were no titratable sulfhydryls in the chicken protein. After denaturation of the crocodilian protein in sodium dodecyl sulfate at 100 degrees C the number of titratable sulfhydryls was 4. Chicken ovomacroglobulin again did not have an appreciable number of titratable sulfhydryls under similar denaturing conditions. Incubation of crocodilian protein with (14C)methylamine showed an incorporation of at least 2 mol of methylamine per molecule. The result indicated the presence of three intramolecular thiol ester bonds in crocodilian ovomacroglobulin with differential stability against external perturbations.

Arakawa, H.; Osada, T.; Ikai, A.

1986-02-01

216

Geochemical Modeling of Reactions and Partitioning of Trace Metals and Radionuclides during Titration of Contaminated Acidic Sediments  

SciTech Connect

Many geochemical reactions that control aqueous metal concentrations are directly affected by solution pH. However, changes in solution pH are strongly buffered by various aqueous phase and solid phase precipitation/dissolution and adsorption/desorption reactions. The ability to predict acid-base behavior of the soil-solution system is thus critical to predict metal transport under variable pH conditions. This study was undertaken to develop a practical generic geochemical modeling approach to predict aqueous and solid phase concentrations of metals and anions during conditions of acid or base additions. The method of Spalding and Spalding was utilized to model soil buffer capacity and pH-dependent cation exchange capacity by treating aquifer solids as a polyprotic acid. To simulate the dynamic and pH-dependent anion exchange capacity, the aquifer solids were simultaneously treated as a polyprotic base controlled by mineral precipitation/dissolution reactions. An equilibrium reaction model that describes aqueous complexation, precipitation, sorption and soil buffering with pH-dependent ion exchange was developed using HydroGeoChem v5.0 (HGC5). Comparison of model results with experimental titration data of pH, Al, Ca, Mg, Sr, Mn, Ni, Co, and SO{sub 4}{sup 2-} for contaminated sediments indicated close agreement, suggesting that the model could potentially be used to predict the acid-base behavior of the sediment-solution system under variable pH conditions.

Zhang, Fan [ORNL; Parker, Jack C. [University of Tennessee, Knoxville (UTK); Luo, Wensui [ORNL; Spalding, Brian Patrick [ORNL; Brooks, Scott C [ORNL; Watson, David B [ORNL; Jardine, Philip M [ORNL; Gu, Baohua [ORNL

2008-01-01

217

Use of potentiometric detection in (ultra) high performance liquid chromatography and modelling with adsorption/desorption binding kinetics.  

PubMed

Observation of a potentiometric sensor's response behaviour after injection in flow injection analysis at different concentrations allowed studying "on" and "off" kinetics of the analyte's adsorption/diffusion behaviour. The alkaloid metergoline was mostly used as an example. k(on) and k(off) rate constant values were measured, and the association constant K(ass), and ?G values of the analyte-surface interaction were calculated with an adsorption-based model which proved to be fully applicable. k(on) increased by decreasing the sensor dimensions, while koff was unaffected by miniaturization. Increasing acetonitrile concentrations in the running buffer increased k(off), while k(on) was unaffected. The experimentally determined ?G values of the analyte-surface interaction showed a linear relation to the response of the sensor, in mV. This knowledge was applied to optimize the potentiometric detection of plant alkaloids in (U)HPLC. Sub-micromolar detection limits were obtained with the potentiometric detector/(U)HPLC combination. This is the first time that the response rates and the response itself can be modelled accurately for coated wire potentiometric sensors, and it is the first application of a potentiometric detector in UPLC. PMID:23622961

Daems, D; Van Camp, G; Fernandez, M; Guisez, Y; Prinsen, E; Nagels, L J

2013-05-13

218

Cation Diffusion in Fluorapatite  

NASA Astrophysics Data System (ADS)

Diffusion of manganese and uranium has been characterized in natural and synthetic fluorapatite under dry conditions. The source of diffusant for Mn experiments were mixtures of ground synthetic or natural fluorapatite and MnO powder, heated in sealed silica glass capsules prior to diffusion anneals. Mn experiments were run by sealing source and apatite in silica glass capsules under vacuum, and annealing capsules in 1 atm furnaces for times ranging from thirty minutes to a few months, at temperatures from 650 to 1050°C. The Mn distributions in the apatite were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation is obtained for Mn diffusion in natural Durango fluorapatite, for diffusion parallel to c: DMn = 5.4x10-7exp(-288 kJ mol-1/RT)m2sec-1. Mn diffusion normal to c appears to be similar to diffusion parallel to c, and diffusivities in natural and synthetic fluorapatite are the same within experimental uncertainties. Uranium diffusion experiments were run with a U-doped microcrystalline apatite source, made through solid-state reaction of UO2, CaF2 and Ca3(PO4)2 under buffered (NNO) conditions. The source and apatite specimens were loaded into Pt capsules, then sealed under vacuum in silica glass capsules with a solid buffer (NNO). Preliminary results over the temperature range 1150-1250°C yield the following Arrhenius relation: DU = 1.4x10-2exp(-511 kJ mol-1/RT)m2sec-1. Diffusivities of Mn are comparable to those of Sr (Cherniak and Ryerson, 1993), and slightly slower than Pb (Cherniak et al., 1991) in apatite. The ionic radii for divalent Mn, Sr, and Pb are 0.90, 1.21 and 1.23 Å, respectively, in 7-fold coordination (Shannon, 1976), and 1.00, 1.31, and 1.35 Å in 9-fold. The similar diffusion rates for Sr and Mn, despite their significant differences in cationic radii, suggest that cation size does not exert strong influence on diffusion of divalent cations in apatite, a finding consistent with that observed for the trivalent REE. Cation charge, however, does seem to more significantly influence diffusivities in apatite. U diffusion is about 4 orders of magnitude slower than Mn diffusion, and about 2 orders of magnitude slower than REE diffusion (Cherniak, 2000). Further, these results suggest that the activation energy for U diffusion is significantly higher than those for divalent cations or trivalent REE. Cherniak et al. (1991) GCA 55, 1663-1673; Cherniak and Ryerson (1993) GCA 57, 4653-4662; Cherniak (2000) GCA 64, 3871-3885; Shannon (1976) Acta Cryst. A32, 751-767.

Cherniak, D. J.

2002-12-01

219

Fusion of Potentiometric & Voltammetric Electronic Tongue for Classification of Black Tea Taste based on Theaflavins (TF) Content  

NASA Astrophysics Data System (ADS)

Black tea is an extensively consumed beverage worldwide with an expanding market. The final quality of black tea depends upon number of chemical compounds present in the tea. Out of these compounds, theaflavins (TF), which is responsible for astringency in black tea, plays an important role in determining the final taste of the finished black tea. The present paper reports our effort to correlate the theaflavins contents with the voltammetric and potentiometric electronic tongue (e-tongue) data. Noble metal-based electrode array has been used for collecting data though voltammetric electronic tongue where as liquid filled membrane based electrodes have been used for potentiometric electronic tongue. Black tea samples with tea taster score and biochemical results have been collected from Tea Research Association, Tocklai, India for the analysis purpose. In this paper, voltammetric and potentiometric e-tongue responses are combined to demonstrate improvement of cluster formation among tea samples with different ranges of TF values.

Bhattacharyya, Nabarun; Legin, Andrey; Papieva, Irina; Sarkar, Subrata; Kirsanov, Dmitry; Kartsova, Anna; Ghosh, Arunangshu; Bandyopadhyay, Rajib

2011-09-01

220

Potentiometric surface map of the Floridan Aquifer in the St Johns River Water Management District and vicinity, Florida, September, 1977  

USGS Publications Warehouse

This map presents the potentiometric surface of the Floridan aquifer in the St. Johns River Water Management District and vicinity for September 1977. The Floridan aquifer is the principal source of potable water in the area. Water-level measurements were made on approximately 900 wells and springs. The potentiometric surface is shown by 5-foot contours except in the Fernandina Beach area where 10- and 20-foot contours are used to show the deep cone of depression. This is the first map covering the entire St. Johns River Water Management District and vicinity for September, a high water-level period. The potentiometric surface ranged from 130 feet above mean sea level in Polk County to 131 feet below sea level in Nassau County. (Woodard-USGS)

Watkins, F.A.; Laughlin, C.P.; Hayes, E.C.

1977-01-01

221

Underground Test Area Subproject Phase I Data Analysis Task. Volume II - Potentiometric Data Document Package  

SciTech Connect

Volume II of the documentation for the Phase I Data Analysis Task performed in support of the current Regional Flow Model, Transport Model, and Risk Assessment for the Nevada Test Site Underground Test Area Subproject contains the potentiometric data. Because of the size and complexity of the model area, a considerable quantity of data was collected and analyzed in support of the modeling efforts. The data analysis task was consequently broken into eight subtasks, and descriptions of each subtask's activities are contained in one of the eight volumes that comprise the Phase I Data Analysis Documentation.

None

1996-12-01

222

A paper-based potentiometric cell for decentralized monitoring of Li levels in whole blood.  

PubMed

A novel approach to monitor Li levels in blood in decentralized (out of the lab) settings is presented. The approach uses a potentiometric cell fully made with filter paper as a support. Electrodes were built using carbon nanotubes ink to create a conductive path and a suitable polymeric membrane. Solid-state ion-selective electrodes for Li and a reference electrode were built and optimized. The results obtained on real samples of serum and whole blood are comparable with those obtained by conventional standard approaches. This platform shows an outstanding performance for the direct, fast and low-cost monitoring of Li levels in blood. PMID:24513977

Novell, Marta; Guinovart, Tomàs; Blondeau, Pascal; Rius, F Xavier; Andrade, Francisco J

2014-04-01

223

Potentiometric maps of the Sparta Sand, northern Louisiana and southern Arkansas, 1900, 1965, 1975, and 1980  

USGS Publications Warehouse

The potentiometric surface of the Sparta Sand in northern Louisiana is shown by contours on four maps. Maps for 1900, 1965 , and spring 1975 are generalized, small-scale maps from previously published reports. The spring 1980 map (1:500,000) is based on measurements in 144 wells and includes the southern tier of counties in southern Arkansas. The map shows regional effects of pumping from the Sparta Sand and effects of local pumping centers at Magnolia and El Dorado, Ark., and at Minden, Ruston, Jonesboro-Hodge, Winnfield, Bastrop, and in the Monroe area of Louisiana. (USGS)

Ryals, G.N.

1980-01-01

224

Potentiometric surface map for the Cretaceous Aquifer, Virginia Coastal Plain, 1978  

USGS Publications Warehouse

The Atlantic Coastal Plain of Virginia includes 9,600 square miles--all or part of 40 counties east of the Fall Line. The undifferentiated Cretaceous sediments underlying this area are the most productive and extensive source of ground water, from which large withdrawals have been made over the past 40 years. In 1978, withdrawals exceeded 100 million gallons per day. To determine the effect of continued withdrawals, annual synoptic water levels for 1978 were used to prepare a map showing the approximate configuration of the potentiometric surface. (USGS)

Hopkins, Herbert T.; Bower, R.F.; Abe, J.M.; Harsh, J.F.

1980-01-01

225

Utilization of maltodextrin based enantioselective, potentiometric membrane electrodes for the enantioselective assay of S-perindopril.  

PubMed

Enantioselective, potentiometric membrane electrodes (EPMEs) based on carbon paste impregnated with different maltodextrins {dextrose equivalent (DE) 4.0-7.0 (I), 13.0-17.0 (II) and 16.5-19.5 (III)} as chiral selectors for the assay of S-perindopril is described. The proposed electrodes could be reliably employed in the assay of S-perindopril raw material and from its pharmaceutical formulation, Coversyl((R)) tablets. The electrode based on maltodextrin (I) showed the best enantioselectivity and time-stability. The surfaces of the electrodes are easily renewable by simply polishing on an alumina paper. PMID:18969348

Ozoemena, Kenneth I; Stefan, Raluca-Ioana; van Staden, Jacobus F; Aboul-Enein, Hassan Y

2004-03-10

226

Louisiana Ground-Water Map No.13: Hydrogeology and Potentiometric Surface of the Sparta Aquifer in Northern Louisiana, October 1996  

USGS Publications Warehouse

This report describes the thickness and areal extent of the Sparta aquifer, identifies sands within the fresh-water extent of the aquifer, and presents data and a map that illustrate the generalized potentiometric surface (water levels) during October 1996. The report includes a detailed geophysical log, structure contour maps, hydrogeologic sections, and hydrographs of water levels in selected wells. The potentiometric surface-map can be used for determining direction of ground-water flow, hydraulic gradients, and the effects of withdrawals on the aquifer.

Brantly, Jeffrey A.; Seanor, Ronald C.; McCoy, Kaycee L.

2002-01-01

227

Louisiana Ground-Water Map No. 13: Hydrogeology and Potentiometric Surface of the Sparta Aquifer in Northern Louisiana, October 1996  

USGS Publications Warehouse

This report describes the thickness and areal extent of the Sparta aquifer, identifies sands within the fresh-water extent of the aquifer, and presents data and a map that illustrate the generalized potentiometric surface (water levels) during October 1996. The report includes a detailed geophysical log, structure contour maps, hydrogeologic sections, and hydrographs of water levels in selected wells. The potentiometric surface-map can be used for determining direction of ground-water flow, hydraulic gradients, and the effects of withdrawals on the aquifer.

Brantly, Jeffrey A.; Seanor, Ronald C.; McCoy, Kaycee L.

2002-01-01

228

Comparison of various sensors in the potentiometric microdetermination of nitroform and perchlorate with cetylpyridinium chloride  

Microsoft Academic Search

Summary Various organic coatings on spectroscopic graphite as well as several types of uncoated graphite materials were examined as sensors in the precipitation titration of nitroform and perchlorate vs. cetylpyridinium chloride. The polymer used in the coatings was poly(vinyl chloride). The plasticizer of choice was di(ethylhexyl) phthalate (dioctylphthalate) because of its low toxicity and large endpoint breaks. Other plasticizers such

Walter Selig

1983-01-01

229

Ascorbic Acid as a Standard for Iodometric Titrations. An Analytical Experiment for General Chemistry  

NASA Astrophysics Data System (ADS)

Ascorbic acid is suggested as the weighable compound for the standardization of iodine solutions in an analytical experiment in general chemistry. The experiment involves an iodometric titration in which iodine reacts with ascorbic acid, oxidizing it to dehydroascorbic acid. The redox titration endpoint is determined by the first iodine excess that is complexed with starch, giving a deep blue-violet color. The results of the titration of iodine solution using ascorbic acid as a calibration standard were compared with the results acquired by the classic method using a standardized solution of sodium thiosulfate. The standardization of the iodine solution using ascorbic acid was accurate and precise, with the advantages of saving time and avoiding mistakes due to solution preparation. The colorless ascorbic acid solution gives a very clear and sharp titration end point with starch. It was shown by thermogravimetric analysis that ascorbic acid can be dried at 393 K for 2 h without decomposition. This experiment allows general chemistry students to perform an iodometric titration during a single laboratory period, determining with precision the content of vitamin C in pharmaceutical formulations.

Silva, Cesar R.; Simoni, Jose A.; Collins, Carol H.; Volpe, Pedro L. O.

1999-10-01

230

Targeting lipophilic cations to mitochondria  

Microsoft Academic Search

Mitochondrial function and dysfunction contributes to a range of important aspects of biomedical research. Consequently there is considerable interest in developing approaches to modify and report on mitochondria in cells and in vivo. One approach has been to target bioactive molecules to mitochondria by conjugating them to lipophilic cations. Due to the large mitochondrial membrane potential, the cations are accumulated

Michael P. Murphy

2008-01-01

231

Potentiometric urea biosensor utilizing nanobiocomposite of chitosan-iron oxide magnetic nanoparticles  

NASA Astrophysics Data System (ADS)

The iron oxide (Fe3O4) magnetic nanoparticles have been fabricated through a simple, cheap and reproducible approach. Scanning electron microscope, x-rays powder diffraction of the fabricated nanoparticles. Furthermore, the fabrication of potentiometric urea biosensor is carried out through drop casting the initially prepared isopropanol and chitosan solution, containing Fe3O4 nanoparticles, on the glass fiber filter with a diameter of 2 cm and a copper wire (of thickness -500 ?m) has been utilized to extract the voltage signal from the functionalized nanoparticles. The functionalization of surface of the Fe3O4 nanoparticles is obtained by the electrostatically immobilization of urease onto the nanobiocomposite of the chitosan- Fe3O4 in order to enhance the sensitivity, specificity, stability and reusability of urea biosensor. Electrochemical detection procedure has been adopted to measure the potentiometric response over the wide logarithmic concentration range of the 0.1 mM to 80 mM. The Fe3O4 nanoparticles based urea biosensor depicts good sensitivity with ~42 mV per decade at room temperature. Durability of the biosensor could be considerably enhanced by applying a thin layer of the nafion. In addition, the reasonably stable output response of the biosensor has been found to be around 12 sec.

Ali, A.; AlSalhi, M. S.; Atif, M.; Ansari, Anees A.; Israr, M. Q.; Sadaf, J. R.; Ahmed, E.; Nur, O.; Willander, M.

2013-02-01

232

Preliminary investigations on a new disposable potentiometric biosensor for uric acid.  

PubMed

In this paper, uricase, catalase, and electron mediator were coimmobilized on the surface of the tin oxide (SnO2)/indium tin oxide (ITO) glass, to develop a disposable potentiometric uric acid biosensor. The SnO2/ITO glass was employed as a pH sensor, fabricated by sputtering SnO2 thin films on the ITO glass. 3-Glycidyloxypropyltrimethoxysilane (GPTS) was utilized to immobilize uricase, catalase and the electron mediator (ferrocenecarboxylic acid, FcA) on the sensing window. The experimental results reveal that the optimal weight ratio of uricase, FcA to catalase (CAT) is 4:1:2. The sensor responds linearly between 2 mg/dl and 7 mg/dl at pH 7.5, in 20 mM of test solution, with a correlation coefficient of 0.99213. Accordingly, no significant interference was observed when interfering substances, glucose, urea and ascorbic acid, were added to the uric acid solution. Moreover, the recorded voltage was relatively constant during the first 28 days of measurement. Consequently, a potentiometric uric acid biosensor was realized with the advantages of low cost and simple fabrication. PMID:16830944

Liao, Cheng Wei; Chou, Jung Chuan; Sun, Tai Ping; Hsiung, Shen Kan; Hsieh, Jui Hsiang

2006-07-01

233

Simultaneous determination of fermented milk aroma compounds by a potentiometric sensor array.  

PubMed

The paper reports on the application of an electronic tongue for simultaneous determination of ethanol, acetaldehyde, diacetyl, lactic acid, acetic acid and citric acid content in probiotic fermented milk. The alphaAstree electronic tongue by Alpha M.O.S. was employed. The sensor array comprised of seven non-specific, cross-sensitive sensors developed especially for food analysis coupled with a reference Ag/AgCl electrode. Samples of plain, strawberry, apple-pear and forest-fruit flavored probiotic fermented milk were analyzed both by standard methods and by the potentiometric sensor array. The results obtained by these methods were used for the development of neural network models for rapid estimation of aroma compounds content in probiotic fermented milk. The highest correlation (0.967) and lowest standard deviation of error for the training (0.585), selection (0.503) and testing (0.571) subset was obtained for the estimation of ethanol content. The lowest correlation (0.669) was obtained for the estimation of acetaldehyde content. The model exhibited poor performance in average error and standard deviations of errors in all subsets which could be explained by low sensitivity of the sensor array to the compound. The obtained results indicate that the potentiometric electronic tongue coupled with artificial neural networks can be applied as a rapid method for the determination of aroma compounds in probiotic fermented milk. PMID:20801331

Hruskar, Mirjana; Major, Nikola; Krpan, Marina; Vahci?, Nada

2010-09-15

234

Application of Nanostructured TCNQ to Potentiometric Ion-Selective K(+) and Na(+) Electrodes.  

PubMed

A new type of potentiometric solid-state ion-selective electrode (SS-ISE) has been fabricated with an intermediate layer made of 7,7,8,8-tetracyanoquinodimethane (TCNQ) or its ion-radical salts and an ionophore-based ion-selective membrane. To show the influence of the TCNQ layer on electrode selectivity, sodium- and potassium-sensitive membranes were applied. A good Nernstian response with a slope of 59.24 mV/dec in the range from 10(-6.5) to 10(-1) M KCl and 58.68 mV/dec (10(-6) to 10(-1) M NaCl) was observed. The influence of an interfacial water film was assessed by an aqueous-layer test performed during potentiometric measurements. The stability of the electrical potential of the new solid-contact electrodes was tested by performing current-reversal chronopotentiometry, and the capacitance of the electrodes is 132 ?F or 154 ?F for K(+) and Na(+) solid-contact electrodes. These properties confirmed the analytical applicability of TCNQ-based SC-ISEs and should allow the development of a new solid-state ion sensor group. PMID:25551547

Paczosa-Bator, Beata; Pi?k, Magdalena; Piech, Robert

2015-02-01

235

[Research on determination of chemical purity of andrographolide by coulometric titration method].  

PubMed

The determination of chemical purity of andrographolide by coulometric titration method is studied in this paper. The coulometric titration was carried out in a mixture composed of 4 mol x L(-1) hydrochloric acid and 1 mol x L(-1) potassium bromide solution and 1 mol x L(-1) potassium nitrate solution (1:1). Bromine is electrogenerated at the anode and reacts with the andrographolide. The number of electrons involved in the eleatrode reaction is 2. Purity of andrographolide is 99.76% compared with 99.77% utilizing area normalization method by HPLC. The RSD are 0.33% and 0.02% respectively. The results from two methods are consistent, so the determination of chemical purity of andrographolide by coulometric titration method is scientific and feasible. The method is rapid, simple, convenient, sensitive and accurate. The reference material is not essential in the method. The method is suitable for determination of chemical purity of andrographolide. PMID:20617683

Yang, Ning; Yang, Dezhi; Xu, Lishen; Lv, Yang

2010-04-01

236

[Titration curves of beta-lactamases using pH gradient electrophoresis].  

PubMed

The molecular relationships of two types of plasmid-mediated beta-lactamases, TEM-1 (R 111), TEM-2 (RP 4) and OXA-1 (RGN 238), OXA-4 (pMG 90) were analysed by combined isoelectrofocusing-electrophoresis. Titration curves of TEM-1 (pI 5.4) and TEM-2 (pI 5.6) together were consistent with the known substitution of a glutamic acid in the former by a lysin in the latter. When OXA-1 (pI 7.4) and OXA-4 (pI 7.45) were titrated, one single mobility curve was obtained reflecting their structural homogeneity. The titration curve technique will be usefull for the study of structure of beta-lactamases. PMID:3116487

Vedel, G; Picard, B; Paul, G; Philippon, A; Goullet, P; Névot, P

1987-06-01

237

A modified Benesi titration procedure useful to quantify the Lewis and Bronsted sites of solid acids  

SciTech Connect

The Benesi method of acid center titration has been modified using dry box techniques so that only 1 g of sample is required to determine the strength distribution of a given sample. Addition of an excess of sterically hindered pyridine to a second 1-g sample, and subsequent titration with n-butylamine using dry box procedures, also allows the strong Lewis acid sites to be quantitatively assessed. By combination of this titration procedure with the modified Benesi procedure the number of Bronsted sites could be determined accurately. Four classes of solid acids were investigated: {gamma}-alumina, high-silica silica-alumina, fluorided alumina, and WO{sub 3} on Al{sub 2}O{sub 3}.

Murrell, L.L.; Dispenziere, N.C. Jr. (Exxon Research and Engineering Co., Annandale, NJ (USA))

1989-05-01

238

Potentiometric surface and specific conductance of the Sparta and Memphis aquifers in eastern Arkansas, 1995  

USGS Publications Warehouse

The Sparta and Memphis aquifers in eastern and south-central Arkansas are a major source of water for industrial, public supply, and agricultural uses. An estimated 240 million gallons per day was withdrawn from the Sparta and Memphis aquifers in 1995, an increase of about 17 million gallons per day from 1990. During the spring and early summer of 1995, the water level in the Sparta and Memphis aquifers was measured in 145 wells, the specific conductance of 101 ground-water samples collected from those aquifers was measured. Maps of areal distribution of potentiometric surface and specific conductance generated from these data reveal spatial trends in these parameters across the eastern and south-central Arkansas study area. The altitude of the potentiometric surface ranged from about 206 feet below sea level in Union County to about 307 feet above sea level in Saline County. The potentiometric surface of the Sparta and Memphis aquifers contains cones of depression descending below sea level in the central and southern portions of the study area, and a potentiometric high along the western study area boundary. Major recharge areas exhibit potentiometric highs greater than 200 feet above sea level and specific conductance values less than 200 microsiemens per centimeter, and generally are located in the outcrop/subcrop areas on the southern one-third of the western boundary and the northern portion of the study area. The regional direction of ground-water flow is from the north and west to the south and east, away from the outcrop and subcrop and northern regions, except near areas affected by intense ground-water withdrawals; such areas are manifested by large cones of depression centered in Columbia, Jefferson, and Union Counties. The cones of depression in adjoining Columbia and Union Counties are coalescing at or near sea level. The lowest water level measured was about 206 feet below sea level in Union County. Increased specific conductance values were measured in the areas of the cones of depression in Columbia and Union Counties. The cones of depression centered in Jefferson County coincides with an elongate area where ground water in the aquifer has low specific conductance. This area extends eastward from the outcrop/subcrop region of recharge. This extension of ground water with low specific conductance possibly indicates increased ground-water movement to the east-southeast from the outcrop/subcrop area induced by ground- water withdrawals in Jefferson County. Specific conductance increases markedly to the northeast and gradually to the south of this area. Long-term hydrographs of eight wells in the study areas, during the period 1970-1995, reveal water-level declines ranging from less than 0.5 foot per year in Phillips County to more than 2.0 feet per year in Union County. Water-level declines of greater than 1.5 feet per year generally are associated with the cones of depression centered in Columbia, Jefferson, and Union Counties.

Stanton, Gregory P.

1997-01-01

239

Using isothermal titration calorimetry to determine thermodynamic parameters of protein-glycosaminoglycan interactions.  

PubMed

It has now become increasingly clear that a complete atomic description of how biomacromolecules recognize each other requires knowledge not only of the structures of the complexes but also of how kinetics and thermodynamics drive the binding process. In particular, such knowledge is lacking for protein-glycosaminoglycan (GAG) complexes. Isothermal titration calorimetry (ITC) is the only technique that can provide various thermodynamic parameters-enthalpy, entropy, free energy (binding constant), and stoichiometry-from a single experiment. Here we describe different factors that must be taken into consideration in carrying out ITC titrations to obtain meaningful thermodynamic data of protein-GAG interactions. PMID:25325962

Dutta, Amit K; Rösgen, Jörg; Rajarathnam, Krishna

2015-01-01

240

Selective two-step titration of thorium by sulfate displacement of the diethylenetriaminepentaacetic acid complex  

SciTech Connect

Thorium and other metals are complexed with excess diethylenetriaminepentaacetic acid (DTPA) at pH 1.4, the excess DTPA is titrated with Bi(III) to a xylenol orange end point, sulfate is added to complex Th(IV), and the displaced DTPA again is titrated with Bi(III). Of 61 metal ions and nonmetal anions tested, only Ga(III), Sc(III), tungstate, citrate, oxalate, and thiosulfate interfere seriously. Lesser interferences are In(III), Zr(IV), V(IV), and permanganate. The standard deviation is 2 ..mu..g for 56 to 840 ..mu..g Th.

Kiefer, P.

1980-07-01

241

Simultaneous determination of potassium and total fluoride in toothpastes using a SIA system with two potentiometric detectors  

Microsoft Academic Search

A sequential injection analysis (SIA) system has been developed for the first time to quantify potassium and total fluoride in toothpastes and gels used to prevent both dentinal hypersensitivity and dental caries. To enable this simultaneous determination, potentiometric detection, using a conventional fluoride electrode and a tubular potassium selective electrode, formed by a PVC membrane containing valinomycin as ionophore, was

R. Pérez-Olmos; J. C. Soto; N. Zárate; I. Díez

2008-01-01

242

Historical potentiometric surface of the Edwards-Trinity aquifer system and contiguous hydraulically connected units, west-central Texas  

USGS Publications Warehouse

The historical potentiometric-surface map of the Edwards-Trinity aquifer system and contiguous hydraulically connected units is based on 1,789 water-level (or pressure-head) measurements made in wells between December 1915 and November 1969. The mapped data reflect a wide range of rainfall conditions. On the basis of interpretations of historical climatologic data by the National Oceanic and Atmospheric Administration, near- normal rainfall conditions preceded 55 percent of the measurements. Moderately dry conditions preceded 20 percent of the measurements; moderately wet conditions preceded 22 percent of the measurements; very dry conditions preceded less than 1 percent; and very wet conditions preceded 3 percent. The historical potentiometric-surface map represents general predevelopment conditions because negligible ground-water withdrawals existed in most areas when the water-level measurements used to construct the map were made. However, in Bexar, Reeves, Pecos, Reagan, and Upton Counties, early withdrawals caused declines in water levels that are reflected in water-level features shown on the map. Topographic relief and stream or spring drainage are two major factors affecting the configuration of the historical potentiometric surface. The strong influence of stream or spring drainage on the potentiometric surface shows that the regional direction of ground-water movement is largely dictated by the locations of major discharge feature. a

Bush, Peter W.; Ardis, Ann F.; Wynn, Kirby H.

1993-01-01

243

Cation-cation contact pairing in water: Guanidinium  

NASA Astrophysics Data System (ADS)

The formation of like-charge guanidinium-guanidinium contact ion pairs in water is evidenced and characterized by X-ray absorption spectroscopy and first-principles spectral simulations based on molecular dynamics sampling. Observed concentration-induced nitrogen K-edge resonance shifts result from ?* state mixing and the release of water molecules from each first solvation sphere as two solvated guanidinium ions associate into a stacked pair configuration. Possible biological implications of this counterintuitive cation-cation pairing are discussed.

Shih, Orion; England, Alice H.; Dallinger, Gregory C.; Smith, Jacob W.; Duffey, Kaitlin C.; Cohen, Ronald C.; Prendergast, David; Saykally, Richard J.

2013-07-01

244

Polymeric membrane neutral phenol-sensitive electrodes for potentiometric G-quadruplex/hemin DNAzyme-based biosensing.  

PubMed

The first potentiometric transducer for G-quadruplex/hemin DNAzyme-based biosensing has been developed by using potential responses of electrically neutral oligomeric phenols on polymeric membrane electrodes. In the presence of G-quadruplex/hemin DNAzyme and H(2)O(2), monomeric phenols (e.g., phenol, methylphenols, and methoxyphenols) can be condensed into oligomeric phenols. Because both substrates and products are nonionic under optimal pH conditions, these reactions are traditionally not considered in designing potentiometric biosensing schemes. However, in this paper, the electrically neutral oligomeric phenols have been found to induce highly sensitive potential responses on quaternary ammonium salt-doped polymeric membrane electrodes owing to their high lipophilicities. In contrast, the potential responses to monomeric phenolic substrates are rather low. Thus, the G-quadruplex/hemin DNAzyme-catalyzed oxidative coupling of monomeric phenols can induce large potential signals, and the catalytic activities of DNAzymes can be probed. A comparison of potential responses induced by peroxidations of 13 monomeric phenols indicates that p-methoxyphenol is the most efficient substrate for potentiometric detection of G-quadruplex/hemin DNAzymes. Finally, two label-free and separation-free potentiometric DNA assay protocols based on the G-quadruplex/hemin DNAzyme have been developed with sensitivities higher than those of colorimetric and fluorometric methods. Coupled with other features such as reliable instrumentation, low cost, ease of miniaturization, and resistance to color and turbid interferences, the proposed polymeric membrane-based potentiometric sensor promises to be a competitive transducer for peroxidase-mimicking DNAzyme-involved biosensing. PMID:23289675

Wang, Xuewei; Ding, Zhaofeng; Ren, Qingwei; Qin, Wei

2013-02-01

245

Titration of a Solid Acid Monitored by X-Ray Diffraction  

ERIC Educational Resources Information Center

An experiment is described to introduce students to an important class of solid-state reactions while reinforcing concepts of titration by using a pH meter and a powder X-ray diffractometer. The experiment was successful in teaching students the abstract concepts of solid-state structure and diffraction by applying the diffraction concepts learned…

Dungey, Keenan E.; Epstein, Paul

2007-01-01

246

Impairment and Deportment Responses to Different Methylphenidate Doses in Children With ADHD: The MTA Titration Trial  

Microsoft Academic Search

ObjectiveResults of the NIMH Collaborative Multisite Multimodal Treatment Study of Children With Attention-Deficit\\/Hyperactivity Disorder (MTA) were analyzed to determine whether a double-blind, placebo-controlled methylphenidate (MPH) titration trial identified the best MPH dose for each child with attention-deficit\\/hyperactivity disorder (ADHD).

LAURENCE L. GREENHILL; JAMES M. SWANSON; BENEDETTO VITIELLO; MARK DAVIES; WALTER CLEVENGER; MIN WU; L. EUGENE ARNOLD; HOWARD B. ABIKOFF; OSCAR G. BUKSTEIN; C. KEITH CONNERS; GLEN R. ELLIOTT; LILY HECHTMAN; STEPHEN P. HINSHAW; BETSY HOZA; PETER S. JENSEN; HELENA C. KRAEMER; JOHN S. MARCH; JEFFREY H. NEWCORN; JOANNE B. SEVERE; KAREN WELLS; TIMOTHY WIGAL

2001-01-01

247

An Isothermal Titration Calorimetric Method to Determine the Kinetic Parameters of Enzyme Catalytic Reaction  

E-print Network

Chemistry of Stable and Unstable Species, Peking University, Beijing 100871, China Received June 20, 2001 of enzyme. The molar reaction heat was calculated from the titration peak area divided by substrate moles change the reaction curve, it can be used as a probe to dig out other useful information. In this paper

Luhua, Lai

248

Applications of Isothermal Titration Calorimetry in RNA Biochemistry and Andrew L. Feig  

E-print Network

incremental addition of one species (a titrant) into its bind- ing partner (titrate) while monitoring. The integration of each peak in the power versus time curve corresponds to the heat associated with each increment. With that in mind, I have specifically excluded a large body of excellent work in the area of protein

Feig, Andrew

249

Coulometric Titration of Ethylenediaminetetraacetate (EDTA) with Spectrophotometric Endpoint Detection: An Experiment for the Instrumental Analysis Laboratory  

ERIC Educational Resources Information Center

Ethylenediaminetetraacetate (EDTA) is commonly used as an anticoagulant in blood-collection procedures. In this experiment for the instrumental analysis laboratory, students determine the quantity of EDTA in commercial collection tubes by coulometric titration with electrolytically generated Cu[superscript 2+]. The endpoint is detected…

Williams, Kathryn R.; Young, Vaneica Y.; Killian, Benjamin J.

2011-01-01

250

DNA heats up: Energetics of genome ejection from phage revealed by isothermal titration calorimetry.  

E-print Network

1 DNA heats up: Energetics of genome ejection from phage revealed by isothermal titration-stranded DNA into bacteria upon receptor binding in an essentially spontaneous way. This downhill thermodynamic process from the intact virion toward the empty viral capsid plus released DNA is made possible

251

Single-experiment displacement assay for quantifying high-affinity binding by isothermal titration calorimetry.  

PubMed

Isothermal titration calorimetry (ITC) is the gold standard for dissecting the thermodynamics of a biomolecular binding process within a single experiment. However, reliable determination of the dissociation constant (KD) from a single titration is typically limited to the range 100?M>KD>1nM. Interactions characterized by a lower KD can be assessed indirectly by so-called competition or displacement assays, provided that a suitable competitive ligand is available whose KD falls within the directly accessible window. However, this protocol is limited by the fact that it necessitates at least two titrations to characterize one high-affinity inhibitor, resulting in considerable consumption of both sample material and time. Here, we introduce a fast and efficient ITC displacement assay that allows for the simultaneous characterization of both a high-affinity ligand and a moderate-affinity ligand competing for the same binding site on a receptor within a single experiment. The protocol is based on a titration of the high-affinity ligand into a solution containing the moderate-affinity ligand bound to the receptor present in excess. The resulting biphasic binding isotherm enables accurate and precise determination of KD values and binding enthalpies (?H) of both ligands. We discuss the theoretical background underlying the approach, demonstrate its practical application to metal ion chelation, explore its potential and limitations with the aid of simulations and statistical analyses, and elaborate on potential applications to protein-inhibitor interactions. PMID:25461813

Krainer, Georg; Keller, Sandro

2014-11-13

252

Binding of Bovine Serum Albumin to Heparin Determined by Turbidimetric Titration and Frontal Analysis  

E-print Network

Binding of Bovine Serum Albumin to Heparin Determined by Turbidimetric Titration and Frontal albu- min (SA) and heparin (Hp). These two species form soluble complexes, the interaction increasing@chem.iupui.edu. 3 Abbreviations used: PGs, proteoglycans; HSPGs, heparin sulfate proteoglycans; GBM, glomerular

Dubin, Paul D.

253

Charge Density Quantification of Polyelectrolyte Polysaccharides by Conductometric Titration: An Analytical Chemistry Experiment  

ERIC Educational Resources Information Center

An easy analytical method for determination of the charge density of polyelectrolytes, including polysaccharides and other biopolymers, is presented. The basic principles of conductometric titration, which is used in the pulp and paper industry as well as in colloid and interface science, were adapted to quantify the charge densities of a…

Farris, Stefano; Mora, Luigi; Capretti, Giorgio; Piergiovanni, Luciano

2012-01-01

254

On the establishment of adsorption equilibrium in n-butylamine titrations of the surface acidity  

Microsoft Academic Search

Using benzeneazodiphenylamine and Dimethyl Yellow as indicators, the difficulties associated with the establishment of an adsorption equlibrium between n-butylamine, the indicator and the acid centers of the catalyst in their titration by the Benesi method are demonstrated. The concentration of the amine affects the experimental values of surface acidity.

M. Baliková

1975-01-01

255

Technical Note: How long can seawater oxygen samples be stored before titration?  

NASA Astrophysics Data System (ADS)

The concentration of dissolved oxygen in seawater is routinely measured using a standardized titration method that involves analysis shortly after the water sample has been collected. However, none of the existing procedural documents are specific about how soon after collection the titration has to be done. Here, we report on a small number of samples where duplicates were collected and one batch was titrated within days after collection, while the other batch was stored for several weeks before titration. In addition, for a subset of the samples a third batch was taken that was stored like the others but with a particular chemical already added before storage. Comparison between the batches confirms that there is no significant difference between the ones that were stored and the ones that were analyzed sooner, indicating that a month-long storage period is acceptable. The implication of this is that such oxygen samples do not necessarily have to be analyzed while still on the ship; instead, it is possible to transport them ashore for analysis there.

Lankhorst, M.; Chavez, G.; Nam, S. H.; Send, U.

2014-10-01

256

Hydrogen-ion titrations of amino acids and proteins in solutions containing concentrated electrolyte  

SciTech Connect

This report describes a first attempt to quantify the net charge as a function of solution pH for lysozyme and {alpha}-chymotrypsin at 0.1 M, 1.0 M and 3.0 M ionic strength, (IS). The calculations are based on the residue (titratable group) pK{sub a}`s in the amino-acid sequence of the protein. To determine these pK{sub a}`s, a simple theory was used which assumes that the pK{sub a}`s are independent from each other in the protein and are equal to their pK{sub a} values in free amino-acid solution (Independent-Site Theory, IST). Residue pK{sub a}`s were obtained from amino-acid hydrogen-ion titrations at three different KCl concentrations corresponding to 0.1M, 1.0M and 3.0M ionic strength. After construction of a suitable apparatus, the experimental procedure and data reduction were computerized to perform a large number of titrations. Most measured pK{sub a}`s showed high reproducibility (the difference of pK{sub a} values observed between two experiments was less than 0.05). For IS = 0.1M, observed pK{sub a}`s agreed with literature values to within a few hundredths of a pH unit. Furthermore, the ionic-strength dependence of the pK{sub a}`s followed the trends reported in the literature, viz. pK{sub a} values decrease with increasing ionic strength until they reach a minimum at about IS = 0.5M. At still higher IS, pK{sub a}`s increase as the ionic strength rises to 3M. The known pK{sub a}`s of all titratable groups in a protein were used with the IST to give a first approximation of how the protein net charge varies with pH at high ionic strength. A comparison of the titration curves based on the IST with experimental lysozyme and {alpha}-chymotrypsin titration data indicates acceptable agreement at IS = 0.1M. However, comparison of measured and calculated titration curves at IS = 1M and IS = 3M indicates only quantitative agreement.

Fergg, F. [Technische Universitaet Muenchen (Germany); Kuehner, D.E.; Blanch, H.W.; Prausnitz, J.M. [Lawrence Berkeley Lab., CA (United States)

1994-12-01

257

Potentiometric biosensor for determination of urea in milk using immobilized Arthrobacter creatinolyticus urease.  

PubMed

The extracellular urease from Arthrobacter creatinolyticus was partially purified by ammonium sulfate precipitation and immobilized on PAN [poly(acrylonitrile-methylmethacrylate-sodium vinylsulfonate)] membrane. The urease immobilized PAN membrane exhibited an activity of 97.92U/cm(2) under the optimum conditions of 1.0% enzyme concentration, 15% glutaraldehyde, 24h immobilization time and temperature of 4°C. The changes in surface morphology of the membrane after immobilization were studied by SEM and ATR-FTIR analysis. Immobilized membrane was associated with potentiometric electrode for calibration of biosensor and the results showed a linear response for wide range of urea concentration from 1 to 100mM. The immobilized urease had good storage stability for a period of 70days at 4°C and could be effectively reused for 13cycles. Urease immobilized membrane was also employed in analysis of urea spiked milk samples. PMID:25687009

Ramesh, Rajendran; Puhazhendi, Puhazhselvan; Kumar, Jitendra; Gowthaman, Marichetti Kuppuswami; D'Souza, Stanislaus Francis; Kamini, Numbi Ramudu

2015-04-01

258

Potentiometric surfaces of the coastal plain aquifers of South Carolina prior to development  

USGS Publications Warehouse

Characteristics of the Coastal Plains aquifers of South Carolina are being studied as a part of the Regional Aquifer Systems Analysis program of the U.S. Geological Survey. A framework has been developed to best represent the hydrology of the Coastal Plain aquifers by dividing them into a system of five aquifers. This framework includes a surficial aquifer consisting of coastal terrace deposits, a limestone and stratigraphically equivalent sand aquifer of Eocene age, and three sand aquifers of Cretaceous age. This report presents a general description of the aquifer framework, potentiometric maps for the aquifers of Eocene and Cretaceous age prior to development, and a general description of the flow system prior to development. In the lower Coastal Plain, flow in the aquifer of Eocene age is generally perpendicular to the coast but is almost parallel to the coast in the aquifers of Cretaceous age. (USGS)

Aucott, Walter R.; Speiran, Gary K.

1985-01-01

259

Potentiometric Electronic Tongue to Resolve Mixtures of Sulfide and Perchlorate Anions  

PubMed Central

This work describes the use of an array of potentiometric sensors and an artificial neural network response model to determine perchlorate and sulfide ions in polluted waters, by what is known as an electronic tongue. Sensors used have been all-solid-state PVC membrane selective electrodes, where their ionophores were different metal-phtalocyanine complexes with specific and anion generic responses. The study case illustrates the potential use of electronic tongues in the quantification of mixtures when interfering effects need to be counterbalanced: relative errors in determination of individual ions can be decreased typically from 25% to less than 5%, if compared to the use of a single proposed ion-selective electrode. PMID:22163795

Wilson, Deivy; Abbas, Mohammed N.; Radwan, Abdel Latief A.; del Valle, Manel

2011-01-01

260

Potentiometric determination of aqueous dissociation constants of flavonols sparingly soluble in water.  

PubMed

Two different approaches were evaluated and used to estimate the aqueous pK(a) values of some flavonols sparingly soluble in water (morin, fisetin and quercetin) from their pK(a) values in methanol/water mixtures obtained by potentiometry. Both approaches lead to similar results, although one of them requires only one pK(a) value at one unique methanol/water mixture, whereas the other (the classical Yasuda-Shedlovsky plot) requires several pK(a) data at different methanol/water mixtures. Thus, the first approach is recommended because it is faster and simpler. The automated potentiometric method is strongly recommended for pK(a) determination of these types of compounds because of its simplicity and speed of operation. PMID:18371741

Herrero-Martínez, José M; Repollés, Carme; Bosch, Elisabeth; Rosés, Martí; Ràfols, Clara

2008-01-15

261

Two Analyte Calibration From The Transient Response Of Potentiometric Sensors Employed With The SIA Technique  

NASA Astrophysics Data System (ADS)

Calibration models for multi-analyte electronic tongues have been commonly built using a set of sensors, at least one per analyte under study. Complex signals recorded with these systems are formed by the sensors' responses to the analytes of interest plus interferents, from which a multivariate response model is then developed. This work describes a data treatment method for the simultaneous quantification of two species in solution employing the signal from a single sensor. The approach used here takes advantage of the complex information recorded with one electrode's transient after insertion of sample for building the calibration models for both analytes. The departure information from the electrode was firstly processed by discrete wavelet for transforming the signals to extract useful information and reduce its length, and then by artificial neural networks for fitting a model. Two different potentiometric sensors were used as study case for simultaneously corroborating the effectiveness of the approach.

Cartas, Raul; Mimendia, Aitor; Legin, Andrey; del Valle, Manel

2009-05-01

262

Determination of baclofen enantiomers in pharmaceutical formulations using maltodextrin-based enantioselective, potentiometric membrane electrodes.  

PubMed

Two enantioselective, potentiometric membrane electrodes (EPMEs) based on maltodextrins with different value of dextrose equivalent (DE) (maltodextrin I: DE 4.0-7.0; maltodextrin II: DE 16.5-19.5) were proposed for the assay of baclofen enantiomers in baclofen raw materials and from its pharmaceutical formulation, Norton-Baclofen tablets. The slopes of the electrode function of the proposed electrodes were 55.0 mV/pS-baclofen for maltodextrin I-based electrode and 59.0 mV/pR-baclofen for maltodextrin II-based electrode and the detection limits were 1.34 x 10(-6) mol l(-1) (S-baclofen) and 2.52 x 10(-10) mol l(-1) (R-baclofen), respectively. The surfaces of the electrodes are stable and easily renewable by simply polishing on alumina paper. PMID:15598435

Rat'ko, Alexander A; Stefan-van Staden, Raluca-Ioana

2004-12-01

263

Determination of water samples and ene-diols or thiols in samples inaccessible for direct K.Fischer titration.  

PubMed

Novel reagents and the rapid technique were developed for the simultaneous determination of water and ene-diols or thiols in chemical products, drugs and other materials which are inaccessible for direct K.Fischer titration. The reagents consist of iodine, tetramethylammonium iodide or potassium iodide, base (diethanolamine, triethanolamine, sodium acetate and/or urea) in methanol mixed with N,N-dimethylformamide, or with formamide, or with dimethyl sulfoxide and N,N-dimethylformamide mixture as a solvent. The use of the reagents is based on the consecutive titration first of an ene-diol or thiol by the novel reagents and then of water by a conventional K.Fischer reagent in the same cell in a titration system protected from water vapour and oxygen, with a double burette and electrometric location of the end point in both titrations. The time for both titrations is 8-15 min. PMID:18966577

Sherman, F; Kuselman, I; Shenhar, A

1996-07-01

264

Real-time telemetry system for amperometric and potentiometric electrochemical sensors.  

PubMed

A real-time telemetry system, which consists of readout circuits, an analog-to-digital converter (ADC), a microcontroller unit (MCU), a graphical user interface (GUI), and a radio frequency (RF) transceiver, is proposed for amperometric and potentiometric electrochemical sensors. By integrating the proposed system with the electrochemical sensors, analyte detection can be conveniently performed. The data is displayed in real-time on a GUI and optionally uploaded to a database via the Internet, allowing it to be accessed remotely. An MCU was implemented using a field programmable gate array (FPGA) to filter noise, transmit data, and provide control over peripheral devices to reduce power consumption, which in sleep mode is 70 mW lower than in operating mode. The readout circuits, which were implemented in the TSMC 0.18-?m CMOS process, include a potentiostat and an instrumentation amplifier (IA). The measurement results show that the proposed potentiostat has a detectable current range of 1 nA to 100 ?A, and linearity with an R2 value of 0.99998 in each measured current range. The proposed IA has a common-mode rejection ratio (CMRR) greater than 90 dB. The proposed system was integrated with a potentiometric pH sensor and an amperometric nitrite sensor for in vitro experiments. The proposed system has high linearity (an R2 value greater than 0.99 was obtained in each experiment), a small size of 5.6 cm × 8.7 cm, high portability, and high integration. PMID:22164093

Wang, Wei-Song; Huang, Hong-Yi; Chen, Shu-Chun; Ho, Kuo-Chuan; Lin, Chia-Yu; Chou, Tse-Chuan; Hu, Chih-Hsien; Wang, Wen-Fong; Wu, Cheng-Feng; Luo, Ching-Hsing

2011-01-01

265

Indirect determination of fluoride by EDTA back-titration of lanthanum.  

PubMed

Semimicro to macro amounts of fluoride ion (0.4-100 mg) are determined rapidly and accurately by precipitation with an excess of lanthanum at pH 2.5-2.8 by digestion on a water-bath, cooling to room temperature, addition of excess of EDTA and back-titration of the excess with zinc solution to the Xylenol Orange end-point at ph 5.8-5..9. Large amounts of chloride, acetate and perchlorate, and small amounts of sulphate and silicate do not interfere, but phosphate does. This method is much superior to the usual thorium nitrate titration method and can be applied after preliminary separation of fluorine by steam distillation or pyrolysis. PMID:18962019

Murase, K; Nakagawa, G; Kodama, K; Shiraishi, N

1977-01-01

266

Successful management of a difficult cancer pain patient by appropriate adjuvant and morphine titration.  

PubMed

Morphine has been used for many years to relieve cancer pain. Oral morphine (in either immediate release or modified release form) remains the analgesic of choice for moderate or severe cancer pain. The dose of oral morphine is titrated up to achieve adequate relief from pain with minimal side effects. Antidepressant and anticonvulsant drugs, when used in addition to conventional analgesics, give excellent relief from cancer pain. Most cancer pain responds to pharmacological measures with oral morphine but some pain like neuropathic and bony pain, pain in children and elderly age group, and advanced malignancy pain are very difficult to treat. Here, we report the management of a similar patient of severe cancer pain and the difficulty that we came across during dose titration of oral morphine and adjuvant analgesic. PMID:21976860

Rana, Shiv Ps; Ahmed, Arif; Kumar, Vindo; Chaudhary, Prakash K; Khurana, Deepa; Mishra, Seema

2011-05-01

267

Successful Management of a Difficult Cancer Pain Patient by Appropriate Adjuvant and Morphine Titration  

PubMed Central

Morphine has been used for many years to relieve cancer pain. Oral morphine (in either immediate release or modified release form) remains the analgesic of choice for moderate or severe cancer pain. The dose of oral morphine is titrated up to achieve adequate relief from pain with minimal side effects. Antidepressant and anticonvulsant drugs, when used in addition to conventional analgesics, give excellent relief from cancer pain. Most cancer pain responds to pharmacological measures with oral morphine but some pain like neuropathic and bony pain, pain in children and elderly age group, and advanced malignancy pain are very difficult to treat. Here, we report the management of a similar patient of severe cancer pain and the difficulty that we came across during dose titration of oral morphine and adjuvant analgesic. PMID:21976860

Rana, Shiv PS; Ahmed, Arif; Kumar, Vindo; Chaudhary, Prakash K; Khurana, Deepa; Mishra, Seema

2011-01-01

268

Implementation of a titrated oxygen protocol in the out-of-hospital setting.  

PubMed

Oxygen is one of the most frequently-used therapeutic agents in medicine and the most commonly administered drug by prehospital personnel. There is increasing evidence of harm with too much supplemental oxygen in certain conditions, including stroke, chronic obstructive pulmonary disease (COPD), neonatal resuscitations, and in postresuscitation care. Recent guidelines published by the British Thoracic Society (BTS) advocate titrated oxygen therapy, but these guidelines have not been widely adapted in the out-of-hospital setting where high-flow oxygen is the standard. This report is a description of the implementation of a titrated oxygen protocol in a large urban-suburban Emergency Medical Services (EMS) system and a discussion of the practical application of this out-of-hospital protocol. PMID:24983332

Bosson, Nichole; Gausche-Hill, Marianne; Koenig, William

2014-08-01

269

Determination of the catalytic activity of binuclear metallohydrolases using isothermal titration calorimetry.  

PubMed

Binuclear metallohydrolases are a large and diverse family of enzymes that are involved in numerous metabolic functions. An increasing number of members find applications as drug targets or in processes such as bioremediation. It is thus essential to have an assay available that allows the rapid and reliable determination of relevant catalytic parameters (k cat, K m, and k cat/K m). Continuous spectroscopic assays are frequently only possible by using synthetic (i.e., nonbiological) substrates that possess a suitable chromophoric marker (e.g., nitrophenol). Isothermal titration calorimetry, in contrast, affords a rapid assay independent of the chromophoric properties of the substrate-the heat associated with the hydrolytic reaction can be directly related to catalytic properties. Here, we demonstrate the efficiency of the method on several selected examples of this family of enzymes and show that, in general, the catalytic parameters obtained by isothermal titration calorimetry are in good agreement with those obtained from spectroscopic assays. PMID:24414447

Pedroso, Marcelo M; Ely, Fernanda; Lonhienne, Thierry; Gahan, Lawrence R; Ollis, David L; Guddat, Luke W; Schenk, Gerhard

2014-03-01

270

Coulometric Karl Fischer titration of trace water in diaphragm-free cells  

Microsoft Academic Search

Factors influencing the accuracy and precision for diaphragm-free Karl Fischer coulometric determinations of low ?g-amounts of water have been studied using the Metrohm 756 (pulsed current) coulometer and eight different types of commercial coulometric reagents and some modifications of these. As in the case of diaphragm-free coulometric titration of large amounts of water, the positive errors, due to the formation

William Larsson; Anders Cedergren

2005-01-01

271

Thermodynamics of IonInduced RNA Folding in the Hammerhead Ribozyme: An Isothermal Titration Calorimetric Study †  

Microsoft Academic Search

The hammerhead ribozyme undergoes a well-defined two-stage conformational folding process, induced by the binding of magnesium ions. In this study, we have used isothermal titration calorimetry to analyze the thermodynamics of magnesium binding and magnesium ion-induced folding of the ribozyme. Binding to the natural sequence ribozyme is strongly exothermic and can be analyzed in terms of sequential interaction at two

Christian Hammann; Alan Cooper; David M. J. Lilley

2001-01-01

272

Kinetic titration with differential thermometric determination of the end-point.  

PubMed

A method has been described for the determination of concentrations below 10(-4)M by applying catalytic reactions and using thermometric end-point determination. A reference solution, identical with the sample solution except for catalyst, is titrated with catalyst solution until the rates of reaction become the same, as shown by a null deflection on a galvanometer connected via bridge circuits to two opposed thermistors placed in the solutions. PMID:18960338

Sajó, I

1968-06-01

273

31P NMR and isothermal titration calorimetry studies on polyoxomolybdates-catalyzed hydrolysis of ATP  

Microsoft Academic Search

ATP hydrolysis in the presence of polyoxomolybdates at pH levels of 6, 4, and 2 has been investigated with a help of high pressure liquid chromatography (HPLC) analyses, 31P- and 1H NMR measurements, and isothermal titration calorimetry (ITC). The polyoxomolybdates-induced ATP-hydrolysis proceeded satisfactorily in pH<6 media at 20°C with an optimum pH level of 4, while it was significantly depressed

Eri Ishikawa; Toshihiro Yamase

2006-01-01

274

A Geochemical Reaction Model for Titration of Contaminated Soil and Groundwater at the Oak Ridge Reservation  

NASA Astrophysics Data System (ADS)

This study investigates geochemical reactions during titration of contaminated soil and groundwater at the Oak Ridge Reservation in eastern Tennessee. The soils and groundwater exhibits low pH and high concentrations of aluminum, calcium, magnesium, manganese, various trace metals such as nickel and cobalt, and radionuclides such as uranium and technetium. The mobility of many of the contaminant species diminishes with increasing pH. However, base additions to increase pH are strongly buffered by various precipitation/dissolution and adsorption/desorption reactions. The ability to predict acid-base behavior and associated geochemical effects is thus critical to evaluate remediation performance of pH manipulation strategies. This study was undertaken to develop a practical but generally applicable geochemical model to predict aqueous and solid-phase speciation during soil and groundwater titration. To model titration in the presence of aquifer solids, an approach proposed by Spalding and Spalding (2001) was utilized, which treats aquifer solids as a polyprotic acid. Previous studies have shown that Fe and Al-oxyhydroxides strongly sorb dissolved Ni, U and Tc species. In this study, since the total Fe concentration is much smaller than that of Al, only ion exchange reactions associated with Al hydroxides are considered. An equilibrium reaction model that includes aqueous complexation, precipitation, ion exchange, and soil buffering reactions was developed and implemented in the code HydroGeoChem 5.0 (HGC5). Comparison of model results with experimental titration curves for contaminated groundwater alone and for soil- water systems indicated close agreement. This study is expected to facilitate field-scale modeling of geochemical processes under conditions with highly variable pH to develop practical methods to control contaminant mobility at geochemically complex sites.

Zhang, F.; Parker, J. C.; Gu, B.; Luo, W.; Brooks, S. C.; Spalding, B. P.; Jardine, P. M.; Watson, D. B.

2007-12-01

275

Acid-base titrations using microfluidic paper-based analytical devices.  

PubMed

Rapid and simple acid-base titration was accomplished using a novel microfluidic paper-based analytical device (?PAD). The ?PAD was fabricated by wax printing and consisted of ten reservoirs for reaction and detection. The reaction reservoirs contained various amounts of a primary standard substance, potassium hydrogen phthalate (KHPth), whereas a constant amount of phenolphthalein was added to all the detection reservoirs. A sample solution containing NaOH was dropped onto the center of the ?PAD and was allowed to spread to the reaction reservoirs where the KHPth neutralized it. When the amount of NaOH exceeded that of the KHPth in the reaction reservoirs, unneutralized hydroxide ion penetrated the detection reservoirs, resulting in a color reaction from the phenolphthalein. Therefore, the number of the detection reservoirs with no color change determined the concentration of the NaOH in the sample solution. The titration was completed within 1 min by visually determining the end point, which required neither instrumentation nor software. The volumes of the KHPth and phenolphthalein solutions added to the corresponding reservoirs were optimized to obtain reproducible and accurate results for the concentration of NaOH. The ?PADs determined the concentration of NaOH at orders of magnitude ranging from 0.01 to 1 M. An acid sample, HCl, was also determined using Na2CO3 as a primary standard substance instead of KHPth. Furthermore, the ?PAD was applicable to the titrations of nitric acid, sulfuric acid, acetic acid, and ammonia solutions. The ?PADs were stable for more than 1 month when stored in darkness at room temperature, although this was reduced to only 5 days under daylight conditions. The analysis of acidic hot spring water was also demonstrated in the field using the ?PAD, and the results agreed well with those obtained by classic acid-base titration. PMID:25423320

Karita, Shingo; Kaneta, Takashi

2014-12-16

276

All-solid-state potentiometric sensors for ascorbic acid by using a screen-printed compatible solid contact  

Microsoft Academic Search

The development of all-solid-state potentiometric ion selective electrodes for monitoring of ascorbic acid, by using a screen-printed compatible solid contact is described. The applied methodology is based on the use of PVC membrane modified with some firstly-tested ionophores (triphenyltin(IV)chloride, triphenyltin(IV)hydroxide and palmitoyl-l-ascorbic acid) and a novel one synthesized in our laboratory (dibutyltin(IV) diascorbate). Synthesis protocol and some preliminary identification studies

Panayotis G. Veltsistas; Mamas I. Prodromidis; Constantinos E. Efstathiou

2004-01-01

277

All Solid-State Potentiometric Biosensors for Creatinine Determination Based on pH and Ammonium Electrodes  

Microsoft Academic Search

This work investigates a disposable creatinine potentiometric biosensor based on a pH-sensitive electrode and an ammonium ion-selective electrode. An enzyme, creatinine iminohydrolase (CIH) was immobilized directly onto the surface of the electrodes by the entrapment method. According to the experimental results, the creatinine biosensors based on the pH-sensitive electrode and ammonium ion-selective electrode show a rapid response time (t95 <

Nien-Hsuan Chou; Jung-Chuan Chou; Tai-Ping Sun; Shen-Kan Hsiung

2009-01-01

278

EPR monitored redox titration of the cofactors of Saccharomyces cerevisiae Nar1.  

PubMed

Electron Paramagnetic Resonance (EPR) monitored redox titrations are a powerful method to determine the midpoint potential of cofactors in proteins and to identify and quantify the cofactors in their detectable redox state. The technique is complementary to direct electrochemistry (voltammetry) approaches, as it does not offer information on electron transfer rates, but does establish the identity and redox state of the cofactors in the protein under study. The technique is widely applicable to any protein containing an electron paramagnetic resonance (EPR) detectable cofactor. A typical titration requires 2 ml protein with a cofactor concentration in the range of 1-100 µM. The protein is titrated with a chemical reductant (sodium dithionite) or oxidant (potassium ferricyanide) in order to poise the sample at a certain potential. A platinum wire and a Ag/AgCl reference electrode are connected to a voltmeter to measure the potential of the protein solution A set of 13 different redox mediators is used to equilibrate between the redox cofactors of the protein and the electrodes. Samples are drawn at different potentials and the Electron Paramagnetic Resonance spectra, characteristic for the different redox cofactors in the protein, are measured. The plot of the signal intensity versus the sample potential is analyzed using the Nernst equation in order to determine the midpoint potential of the cofactor. PMID:25490157

Hagedoorn, Peter-Leon; van der Weel, Laura; Hagen, Wilfred R

2014-01-01

279

Chaotic dynamics of resting ventilatory flow in humans assessed through noise titration  

E-print Network

The mammalian ventilatory behavior exhibits nonlinear dynamics as reflected by certain nonlinearity or complexity indicators (e.g. correlation dimension, approximate entropy, Lyapunov exponents...) but this is not sufficient to determine its possible chaotic nature. To address this, we applied the noise titration technique, previously shown to discern and quantify chaos in short and noisy time series, to ventilatory flow recordings obtained in quietly breathing normal humans. Nine subjects (8 men and 1 woman, 24-42 yrs) were studied during 15-minute epochs of ventilatory steady-state (10.1 +/- 3.0 breaths/minute, tidal volume 0.63 +/- 0.2L). Noise titration applied to the unfiltered signals subsampled at 5 Hz detected nonlinearity in all cases (noise limit 20.2 +/- 12.5%). Noise limit values were weakly correlated to the correlation dimension and the largest Lyapunov exponent of the signals. This study shows that the noise titration approach evidences a chaotic dimension to the behavior of ventilatory flow over time in normal humans during tidal breathing.

Marc Wysocki; Marie-Noelle Fiamma; Christian Straus; Chi-Sang Poon; Thomas Similowski

2006-06-12

280

Statistical mechanical model of coupled transcription from multiple promoters due to transcription factor titration  

PubMed Central

Transcription factors (TFs) with regulatory action at multiple promoter targets is the rule rather than the exception, with examples ranging from the cAMP receptor protein (CRP) in E. coli that regulates hundreds of different genes simultaneously to situations involving multiple copies of the same gene, such as plasmids, retrotransposons, or highly replicated viral DNA. When the number of TFs heavily exceeds the number of binding sites, TF binding to each promoter can be regarded as independent. However, when the number of TF molecules is comparable to the number of binding sites, TF titration will result in correlation (“promoter entanglement”) between transcription of different genes. We develop a statistical mechanical model which takes the TF titration effect into account and use it to predict both the level of gene expression for a general set of promoters and the resulting correlation in transcription rates of different genes. Our results show that the TF titration effect could be important for understanding gene expression in many regulatory settings. PMID:24580252

Rydenfelt, Mattias; Cox, Robert Sidney; Garcia, Hernan; Phillips, Rob

2014-01-01

281

Calorimetry, activity, and micro-FTIR analysis of CO chemisorption, titration, and oxidation on supported Pt  

NASA Technical Reports Server (NTRS)

The value of in situ analysis on CO chemisorption, titration and oxidation over supported Pt catalysts using calorimetry, catalytic and micro-FTIR methods is illustrated using silica- and titania-supported samples. Isothermal CO-O and O2-CO titrations have not been widely used on metal surfaces and may be complicated if some oxide supports are reduced by CO titrant. However, they can illuminate the kinetics of CO oxidation on metal/oxide catalysts since during such titrations all O and CO coverages are scanned as a function of time. There are clear advantages in following the rates of the catalyzed CO oxidation via calorimetry and gc-ms simultaneously. At lower temperatures the evidence they provide is complementary. CO oxidation and its catalysis of CO oxidation have been extensively studied with hysteresis and oscillations apparent, and the present results suggest the benefits of a combined approach. Silica support porosity may be important in defining activity-temperature hysteresis. FTIR microspectroscopy reveals the chemical heterogeneity of the catalytic surfaces used; it is interesting that the evidence with regard to the dominant CO surface species and their reactivities with regard to surface oxygen for present oxide-supported Pt are different from those seen on graphite-supported Pt.

Sermon, Paul A.; Self, Valerie A.; Vong, Mariana S. W.; Wurie, Alpha T.

1990-01-01

282

Rapid and Automated Analytical Methods for Redox Species Based on Potentiometric Flow Injection Analysis Using Potential Buffers  

PubMed Central

Two analytical methods, which prove the utility of a potentiometric flow injection technique for determining various redox species, based on the use of some redox potential buffers, are reviewed. The first is a potentiometric flow injection method in which a redox couple such as Fe(III)-Fe(II), Fe(CN)6?3?-Fe(CN)(CN)6?4?, and bromide-bromine and a redox electrode or a combined platinum-bromide ion selective electrode are used. The analytical principle and advantages of the method are discussed, and several examples of its application are reported. Another example is a highly sensitive potentiometric flow injection method, in which a large transient potential change due to bromine or chlorine as an intermediate, generated during the reaction of the oxidative species with an Fe(III)-Fe(II) potential buffer containing bromide or chloride, is utilized. The analytical principle and details of the proposed method are described, and examples of several applications are described. The determination of trace amounts of hydrazine, based on the detection of a transient change in potential caused by the reaction with a Ce(IV)-Ce(III) potential buffer, is also described. PMID:21584280

Ohura, Hiroki; Imato, Toshihiko

2011-01-01

283

USING WOOD AND BONE ASH TO REMOVE METAL IONS FROM SOLUTIONS  

Microsoft Academic Search

In the present work, wood and bone ash were used to remove metal cations from solutions. Cation-removal capacity of the ashes was analyzed by potentiometric titration. It was found that the capacity of wood ash was two times higher (37.3 meq g-1) than bone ash (15.2 meq g-1). Kinetics of metal ions removal by both ashes was described with pseudo-second

K. CHOJNACKA; I. MICHALAK

284

Non-Surface Activity of Cationic Amphiphilic Diblock Copolymers  

NASA Astrophysics Data System (ADS)

Cationic amphiphilic diblock copolymers containing quaternized poly (2-vinylpyridine) chain as a hydrophilic segment (PIp-b-PNMe2VP) were synthesized by living anionic polymerization. By IR measurement, we confirmed the quaternization of the polymer (PIp-b-PNMe2VP), and determined the degree of quaternization by conductometric titration. The surface tension experiment showed that the polymers are non-surface active in nature. The foam formation of the polymer solutions was also investigated with or without added salt. Almost no foam formation behavior was observed without added salt, while a little foam was observed in the presence of 1M NaCl. The critical micelle concentration (cmc) of the diblock copolymers with 3 different chain lengths was measured by the static light scattering method. The cmc values obtained in this study were much lower than the values obtained for anionic non-surface active diblock polymers studied previously. The hydrodynamic radii of the polymer micelle increased slightly in the presence of 1 M NaCl. The transmission electron microscopic images revealed spherical micelles in pure water. In the presence of salt, the cmc values increased as was the case for anionic polymers, which is unlike conventional surfactant systems but consistent with non-surface active anionic block copolymers. The microviscosity of the micelle core was evaluated using Coumarin-153 as a fluorescent anisotropy probe using steady-sate fluorescence depolarization. Non-surface activity has been proved to be universal for ionic amphiphilic block copolymers both for anionic and cationic. Hence, the origin of non-surface activity is not the charged state of water surface itself, but should be an image charge repulsion at the air/water interface.

Ranjan Nayak, Rati; Yamada, Tasuku; Matsuoka, Hideki

2011-09-01

285

Sequential injection with lab-at-valve (LAV) approach for potentiometric determination of chloride.  

PubMed

Sequential injection with "Lab-at-Valve (LAV)" approach is demonstrated for potentiometric determination of chloride. The LAV flow-through electrode system consists of two Ag/AgCl electrodes: one as a reference electrode, silver chloride activated surface-silver wire soaked in a constant-concentration chloride ion solution in a small tube covered with a polymer-membrane, another as a working electrode (a similar silver chloride activated surface-silver wire) placed in a flow channel. The electrode system is attached at one port of a 10 port multiposition valve. A modified autoburette was used as a propelling device. Using SI operation via a program written in-house, based on LabVIEW((R)), a standard/sample is inserted, via the selection valve, in potassium nitrate as an electrolyte and water is used as a carrier. The zones are transported from the holding coil to the flow cell to monitor the difference in potential due to concentration cell behavior. The potential difference is then recorded as a peak. Peak height is proportional to logarithm of chloride concentration. The SI-LAV for chloride determination is very simple, fast, precise, accurate, automatic and economical. Applications to mineral drinking water and surface water have been made. The results agree with those of IC and titrimetric methods. PMID:18969869

Jakmunee, Jaroon; Patimapornlert, Lop; Suteerapataranon, Siripat; Lenghor, Narong; Grudpan, Kate

2005-02-15

286

A Potentiometric Formaldehyde Biosensor Based on Immobilization of Alcohol Oxidase on Acryloxysuccinimide-modified Acrylic Microspheres  

PubMed Central

A new alcohol oxidase (AOX) enzyme-based formaldehyde biosensor based on acrylic microspheres has been developed. Hydrophobic poly(n-butyl acrylate-N-acryloxy-succinimide) [poly(nBA-NAS)] microspheres, an enzyme immobilization matrix, was synthesized using photopolymerization in an emulsion form. AOX-poly(nBA-NAS) microspheres were deposited on a pH transducer made from a layer of photocured and self-plasticized polyacrylate membrane with an entrapped pH ionophore coated on a Ag/AgCl screen printed electrode (SPE). Oxidation of formaldehyde by the immobilized AOX resulted in the production of protons, which can be determined via the pH transducer. Effects of buffer concentrations, pH and different amount of immobilization matrix towards the biosensor’s analytical performance were investigated. The formaldehyde biosensor exhibited a dynamic linear response range to formaldehyde from 0.3–316.2 mM and a sensitivity of 59.41 ± 0.66 mV/decade (R2 = 0.9776, n = 3). The lower detection limit of the biosensor was 0.3 mM, while reproducibility and repeatability were 3.16% RSD (relative standard deviation) and 1.11% RSD, respectively (n = 3). The use of acrylic microspheres in the potentiometric formaldehyde biosensor improved the biosensor’s performance in terms of response time, linear response range and long term stability when compared with thick film immobilization methods. PMID:22163450

Ling, Yew Pei; Heng, Lee Yook

2010-01-01

287

A Novel Potentiometric Sensor for Determination of Neurotoxin ?-N-Oxalyl-L-?, ?-Diaminopropionic Acid  

PubMed Central

A novel potentiometric sensor based on ionophore (Cd(NH2CH2CH2OCH2CH2OCH2CH2NH2)Ag3(CN)5) for the determination of ?-N-oxalyl-l-?, ?-diaminopropionic acid (ODAP) is developed. The ODAP-selective membrane sensor demonstrates high sensitivity and short response time. The detection limit of the ODAP-selective membrane sensor is about 2 × 10?6?mol?L-1 and the response time is shorter than 6?s. The linear dynamic range of the ODAP-selective membrane sensor is between ODAP concentrations of 1.0 × 10?2 and 1 × 10?6?mol?L-1. The ODAP-selective membrane sensor exhibits good operational stability for at least one week in dry conditions at 4–6°C. It has a reproducible and stable response during continuous work for at least 10?h with a relative standard deviation of 0.28% (n = 18). PMID:24971325

Isildak, Omer; Saymaz, Furkan; Karadag, Ahmet; Korkmaz, Nesrin Okumus; Attar, Azade

2014-01-01

288

Computational prediction and experimental selectivity coefficients for hydroxyzine and cetirizine molecularly imprinted polymer based potentiometric sensors.  

PubMed

In spite of the increasing usages number of molecularly imprinted polymers (MIPs) in many scientific applications, the theoretical aspects of participating intra molecular forces are not fully understood. This work investigates effects of the electrostatic force, the Mulliken charge and the role of cavity's backbone atoms on the selectivity of MIPs. Moreover, charge distribution, which is a computational parameter, was proposed for the prediction of the selectivity coefficients of MIP-based sensors. In the computational approaches and experimental study, methacrylic acid (MAA) was chosen as the functional monomer and ethylene glycol dimethacrylate (EGDMA) as the cross linker for hydroxyzine and cetirizine imprinted polymers. Ab initio, DFT B3LYP method was carried out on molecular optimization. With regard to results obtained from molecules optimization and hydrogen bonding properties, possible configurations of 1:n (n?5) template/monomer complexes were designed and optimized. The binding energy for each complex in gas phase was calculated. Depending on the most stable configuration, hydroxyzine and cetirizine imprinted polymer models were designed. The calculations including the porogen were also investigated. The theoretical charge distributions for the template and some potential interfering molecules were calculated. The results showed a correlation between the selectivity coefficients and the theoretical charge distributions. The results surprisingly show that charge distribution based model was able to predict the selectivity coefficients of MIP based potentiometric sensors. PMID:24491780

Azimi, Abolfazl; Javanbakht, Mehran

2014-02-17

289

A label-free potentiometric sensor principle for the detection of antibody-antigen interactions.  

PubMed

We report here on a new potentiometric biosensing principle for the detection of antibody-antigen interactions at the sensing membrane surface without the need to add a label or a reporter ion to the sample solution. This is accomplished by establishing a steady-state outward flux of a marker ion from the membrane into the contacting solution. The immunobinding event at the sensing surface retards the marker ion, which results in its accumulation at the membrane surface and hence in a potential response. The ion-selective membranes were surface-modified with an antibody against respiratory syncytial virus using click chemistry between biotin molecules functionalized with a triple bond and an azide group on the modified poly (vinyl chloride) group of the membrane. The bioassay sensor was then built up with streptavidin and subsequent biotinylated antibody. A quaternary ammonium ion served as the marker ion. The observed potential was found to be modulated by the presence of respiratory syncytial virus bound on the membrane surface. The sensing architecture was confirmed with quartz crystal microbalance studies, and stir effects confirmed the kinetic nature of the marker release from the membrane. The sensitivity of the model sensor was compared to that of a commercially available point-of-care test, with promising results. PMID:23534536

Ozdemir, Mahir S; Marczak, Marcin; Bohets, Hugo; Bonroy, Kristien; Roymans, Dirk; Stuyver, Lieven; Vanhoutte, Koen; Pawlak, Marcin; Bakker, Eric

2013-05-01

290

A potentiometric formaldehyde biosensor based on immobilization of alcohol oxidase on acryloxysuccinimide-modified acrylic microspheres.  

PubMed

A new alcohol oxidase (AOX) enzyme-based formaldehyde biosensor based on acrylic microspheres has been developed. Hydrophobic poly(n-butyl acrylate-N-acryloxy-succinimide) [poly(nBA-NAS)] microspheres, an enzyme immobilization matrix, was synthesized using photopolymerization in an emulsion form. AOX-poly(nBA-NAS) microspheres were deposited on a pH transducer made from a layer of photocured and self-plasticized polyacrylate membrane with an entrapped pH ionophore coated on a Ag/AgCl screen printed electrode (SPE). Oxidation of formaldehyde by the immobilized AOX resulted in the production of protons, which can be determined via the pH transducer. Effects of buffer concentrations, pH and different amount of immobilization matrix towards the biosensor's analytical performance were investigated. The formaldehyde biosensor exhibited a dynamic linear response range to formaldehyde from 0.3-316.2 mM and a sensitivity of 59.41 ± 0.66 mV/decade (R(2) = 0.9776, n = 3). The lower detection limit of the biosensor was 0.3 mM, while reproducibility and repeatability were 3.16% RSD (relative standard deviation) and 1.11% RSD, respectively (n = 3). The use of acrylic microspheres in the potentiometric formaldehyde biosensor improved the biosensor's performance in terms of response time, linear response range and long term stability when compared with thick film immobilization methods. PMID:22163450

Ling, Yew Pei; Heng, Lee Yook

2010-01-01

291

Potentiometric investigations of carbonate ion stability in molten cesium and sodium iodides.  

PubMed

The reaction of carbonate ion dissociation in molten CsI and NaI was studied in the temperature range from the melting point to 800 (CsI) and 830 degrees C (NaI) by a potentiometric method with the use of a membrane oxygen electrode as an indicator one. The dissociation constant of CO(3)(2-) in the molten iodides was found to increase with the temperature. pK values for CsI are 4.47 (650 degrees C), 4.23 (700 degrees C), 3.89 (750 degrees C), 3.44 (800 degrees C); those for NaI are 4.68 (700 degrees C), 4.39 (750 degrees C), 4.17 (800 degrees C), 3.92 (830 degrees C). The plots of pK vs reverse temperature are linear. Carbonate stability in molten CsI is lower than that in the NaI due to lower stability of Cs(2)CO(3) compared with Na(2)CO(3). PMID:11874336

Cherginets, Victor L; Demirskaya, Olga V; Rebrova, Tatyana P

2002-03-11

292

Single interface flow system with potentiometric detection for the determination of nitrate in water and vegetables.  

PubMed

In this work a single interface flow system (SIFA) with potentiometric detection was for the first time implemented and applied to the determination of nitrate in waters and plant extracts. The analytical potential of the SIFA system was exploited not only to transport the sample towards detection but also to carry out, in a reproducible and automated way, the tasks associated with sample pre-treatment, namely ionic strength, pH adjustment and interfering species suppression. The advantageous aspects of combining a SIFA system with potentiometry with enhanced simplicity, ease of implementation and automation were further discussed and emphasised. The obtained results showed relative deviations lower than 5%, for both types of samples, with sampling rates of about 40h(-1). In addition, an innovative and straightforward process for constructing plastic membrane ion selective electrodes with a tubular configuration able to be coupled to flow-based analytical systems is also proposed. The developed approach, consisting of assembling the electrode inside a flow tubing connector is very simple to implement, robust, particularly adequate to be combined with flow methodologies and maintains all dynamic and analytical characteristics exhibited by previous assembling processes. PMID:20006095

Santos, João Rodrigo; Santos, João L M; Lima, José L F C

2010-01-15

293

Technical Note: Maximising accuracy and minimising cost of a potentiometrically regulated ocean acidification simulation system  

NASA Astrophysics Data System (ADS)

This article describes a potentiometric ocean acidification simulation system which automatically regulates pH through the injection of 100% CO2 gas into temperature-controlled seawater. The system is ideally suited to long-term experimental studies of the effect of acidification on biological processes involving small-bodied (10-20 mm) calcifying or non-calcifying organisms. Using hobbyist grade equipment, the system was constructed for approximately USD 1200 per treatment unit (tank, pH regulation apparatus, chiller, pump/filter unit). An overall accuracy of ±0.05 pHT units (SD) was achieved over 90 days in two acidified treatments (7.60 and 7.40) at 12 °C using glass electrodes calibrated with salt water buffers, thereby preventing liquid junction error. The accuracy of the system was validated through the independent calculation of pHT (12 °C) using dissolved inorganic carbon (DIC) and total alkalinity (AT) data taken from discrete acidified seawater samples. The system was used to compare the shell growth of the marine gastropod Zeacumantus subcarinatus infected with the trematode parasite Maritrema novaezealandensis with that of uninfected snails, at pH levels of 7.4, 7.6, and 8.1.

MacLeod, C. D.; Doyle, H. L.; Currie, K. I.

2014-05-01

294

Generalized Potentiometric Surface of the Arikaree Aquifer, Pine Ridge Indian Reservation and Bennett County, South Dakota  

USGS Publications Warehouse

INTRODUCTION The Pine Ridge Indian Reservation and Bennett County are located in southwest South Dakota. The Pine Ridge Indian Reservation includes all of Shannon County and the part of Jackson County south of the White River. Extensive Indian trust lands are in Bennett County. For purposes of this map, the Pine Ridge Indian Reservation and all of Bennett County are included in the study area (sheet 1). Ground water from wells and springs is the predominant source of public and domestic supply within the study area. The Arikaree aquifer is the largest source of ground water throughout this area. The Oglala Sioux Tribe is developing a ground-water management plan designed to ?preserve, protect and maintain the quality of ground water for living and future members and non-members of the Oglala Sioux Indian Tribe within the internal and external boundaries of the Pine Ridge Reservation? (Michael Catches Enemy, Oglala Sioux Tribe Natural Resources Regulatory Agency, oral commun., 2007). Hydrologic information about the Arikaree aquifer is important to managing this resource. In 1998, the U.S. Geological Survey (USGS) began working in cooperation with the Oglala Sioux Tribe to develop a potentiometric map of the Arikaree aquifer in Jackson and Shannon Counties, with a primary component of that effort being a well inventory in those counties. In 2003, the study area was expanded to include Bennett County.

Carter, Janet M.; Heakin, Allen J.

2007-01-01

295

Incorporating ?-Cyclodextrin with ZnO Nanorods: A Potentiometric Strategy for Selectivity and Detection of Dopamine  

PubMed Central

We describe a chemical sensor based on a simple synthesis of zinc oxide nanorods (ZNRs) for the detection of dopamine molecules by a potentiometric approach. The polar nature of dopamine leads to a change of surface charges on the ZNR surface via metal ligand bond formation which results in a measurable electrical signal. ZNRs were grown on a gold-coated glass substrate by a low temperature aqueous chemical growth (ACG) method. Polymeric membranes incorporating ?-cyclodextrin (?-CD) and potassium tetrakis (4-chlorophenyl) borate was immobilized on the ZNR surface. The fabricated electrodes were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The grown ZNRs were well aligned and exhibited good crystal quality. The present sensor system displays a stable potential response for the detection of dopamine in 10?2 mol·L?1 acetic acid/sodium acetate buffer solution at pH 5.45 within a wide concentration range of 1 × 10?6 M?1 × 10?1 M, with sensitivity of 49 mV/decade. The electrode shows a good response time (less than 10 s) and excellent repeatability. This finding can contribute to routine analysis in laboratories studying the neuropharmacology of catecholamines. Moreover, the metal-ligand bonds can be further exploited to detect DA receptors, and for bio-imaging applications. PMID:24445413

Elhag, Sami; Ibupoto, Zafar Hussain; Nur, Omer; Willander, Magnus

2014-01-01

296

Evaluation of the 5 and 8 pH point titration methods for monitoring anaerobic digesters treating solid waste.  

PubMed

Simple titration methods certainly deserve consideration for on-site routine monitoring of volatile fatty acid (VFA) concentration and alkalinity during anaerobic digestion (AD), because of their simplicity, speed and cost-effectiveness. In this study, the 5 and 8 pH point titration methods for measuring the VFA concentration and carbonate system alkalinity (H2CO3*-alkalinity) were assessed and compared. For this purpose, synthetic solutions with known H2CO3*-alkalinity and VFA concentration as well as samples from anaerobic digesters treating three different kind of solid wastes were analysed. The results of these two related titration methods were verified with photometric and high-pressure liquid chromatography measurements. It was shown that photometric measurements lead to overestimations of the VFA concentration in the case of coloured samples. In contrast, the 5 pH point titration method provides an accurate estimation of the VFA concentration, clearly corresponding with the true value. Concerning the H2CO3*-alkalinity, the most accurate and precise estimations, showing very similar results for repeated measurements, were obtained using the 8 pH point titration. Overall, it was concluded that the 5 pH point titration method is the preferred method for the practical monitoring of AD of solid wastes due to its robustness, cost efficiency and user-friendliness. PMID:25224566

Vannecke, T P W; Lampens, D R A; Ekama, G A; Volcke, E I P

2015-04-01

297

Determination of free acidic and alkaline residues of protein via moving reaction boundary titration in microdevice electrophoresis.  

PubMed

As two important physico-chemical parameters, the acidic and alkaline residues of protein are of evident significance for the evaluation of protein properties and the design of relevant separation and analysis. However, there is still no electrophoretic method used for the direct detection of free acidic and alkaline residues of protein. Herein, we developed the concepts of moving reaction boundary (MRB) and MRB titration, relevant MRB titration theory, and the method of microdevice electrophoresis for the determination of free acidic and alkaline residues of protein. In the MRB titration, the boundary was created with acid or alkali and target protein immobilized via highly cross-linked polyacrylamide gel (PAG). It was theoretically revealed that the number of free acidic or alkaline residues of protein was as a function of MRB displacement in the electrophoretic titration system. As a proof of concept, seven model proteins were chosen for the determination of acidic or alkaline residues of protein via MRB titration. The results showed that the numbers of free acidic and alkaline residues of proteins detected were in good agreement with those obtained from the relevant amino sequences in the NCBI database, demonstrating the feasibility of the developed concept, theory and technique. The general methodology of MRB titration has potential application for inexpensive, facilitative and informative protein structure analysis of free acidic or alkaline residues of protein. PMID:23671907

Wang, Hou-yu; Li, Si; Tang, Yun-yun; Dong, Jing-yu; Fan, Liu-yin; Cao, Cheng-xi

2013-06-21

298

Cationic electrodepositable coating composition comprising lignin  

DOEpatents

A cationic electrodepositable coating composition is disclosed. The present invention in directed to a cationic electrodepositable coating composition comprising a lignin-containing cationic salt resin, that comprises (A) the reaction product of: lignin, an amine, and a carbonyl compound; (B) the reaction product of lignin, epichlorohydrin, and an amine; or (C) combinations thereof.

Fenn, David; Bowman, Mark P; Zawacky, Steven R; Van Buskirk, Ellor J; Kamarchik, Peter

2013-07-30

299

Resorcarene-based receptor: versatile behavior in its interaction with heavy and soft metal cations.  

PubMed

Standard solution Gibbs energies, DeltasG degrees, of the resorcarene-based receptor 5,11,17,23-ethylthiomethylated calix[4]resorcarene, (characterized by 1H NMR and X-ray diffraction studies) in its monomeric state (established through partition experiments) in various solvents are for the first time reported in the area of resorcarene chemistry. Transfer Gibbs energies of from hexane (reference solvent) to other medium are calculated. Agreement between DeltatG degrees (referred to the pure solvents) and standard partition Gibbs energies, DeltapG degrees (solvent mutually saturated) is found. Cation-ligand interactions were investigated through 1H NMR (CD3CN and CD3OD) and conductometric titrations in acetonitrile and methanol. 1H NMR data revealed the sites of interaction of with the metal cation. The composition of the metal-ion complexes (Ag+ and Pb2+ in acetonitrile and Ag+ and Cu2+ in methanol) was established through conductometric titrations. Thus, complexes of 1:1 stoichiometry were formed between and Ag+ and Pb2+ in acetonitrile and Cu2+ in methanol. However, in moving from acetonitrile to methanol, the composition of the silver complex was altered. Thus, two metal cations are hosted by a unit of the ligand. As far as Cu2+ and in acetonitrile is concerned, conductance data suggest that metalates are formed in which up to four units of Cu2+ are taken up per unit of resorcarene. The contrasting behavior of with Cu2+ in acetonitrile relative to methanol is discussed. As far as mercury (II) is concerned, the unusual jump in conductance observed in the titration of Hg2+ with in acetonitrile and methanol after the formation of a multicharged complex (undefined composition) is attributed to the presence of highly charged smaller units (higher mobility) resulting from the departure of pendant arms from the resorcarene backbone. Isolation of these species followed by X-ray diffraction studies corroborated this statement. The thermodynamic characterization of metal-ion complexes of Ag+ and Pb2+ in acetonitrile and Cu2+ and Ag+ in methanol is reported. Final conclusions are given. PMID:16471836

Danil de Namor, Angela F; Chaaban, Jinane K; Piro, Oscar E; Castellano, Eduardo E

2006-02-01

300

Calorimetric study of cationic photopolymerization  

NASA Astrophysics Data System (ADS)

The photopolymerization of penta-erythritol tetra-glycidyl ether (initiator Degacure KI-85) was studied by a du Pont 910 type DSC. From our experimental results the following conclusions can be drawn: (1) During the cationic polymerization reaction the lifetime of the initiating centers are long compared to the lifetime of free radicals in case of radical polymerization. (2) The rate of deactivation of the initiating centers increases with increasing temperature.

Czajlik, I.; Hedvig, P.; Ille, A.; Dobó, J.

1996-03-01

301

Non-damaging laser therapy of the macula: Titration algorithm and tissue response  

NASA Astrophysics Data System (ADS)

Retinal photocoagulation typically results in permanent scarring and scotomata, which limit its applicability to the macula, preclude treatments in the fovea, and restrict the retreatments. Non-damaging approaches to laser therapy have been tested in the past, but the lack of reliable titration and slow treatment paradigms limited their clinical use. We developed and tested a titration algorithm for sub-visible and non-damaging treatments of the retina with pulses sufficiently short to be used with pattern laser scanning. The algorithm based on Arrhenius model of tissue damage optimizes the power and duration for every energy level, relative to the threshold of lesion visibility established during titration (and defined as 100%). Experiments with pigmented rabbits established that lesions in the 50-75% energy range were invisible ophthalmoscopically, but detectable with Fluorescein Angiography and OCT, while at 30% energy there was only very minor damage to the RPE, which recovered within a few days. Patients with Diabetic Macular Edema (DME) and Central Serous Retinopathy (CSR) have been treated over the edematous areas at 30% energy, using 200?m spots with 0.25 diameter spacing. No signs of laser damage have been detected with any imaging modality. In CSR patients, subretinal fluid resolved within 45 days. In DME patients the edema decreased by approximately 150?m over 60 days. After 3-4 months some patients presented with recurrence of edema, and they responded well to retreatment with the same parameters, without any clinically visible damage. This pilot data indicates a possibility of effective and repeatable macular laser therapy below the tissue damage threshold.

Palanker, Daniel; Lavinsky, Daniel; Dalal, Roopa; Huie, Philip

2014-02-01

302

Synthesis, characterization and analytical application of nano-composite cation-exchange material, poly-o-toluidine Ce(IV) phosphate: Its application in making Cd(II) ion selective membrane electrode  

NASA Astrophysics Data System (ADS)

An organic-inorganic composite, poly-o-toluidine Ce(IV) phosphate was chemically synthesized by mixing ortho-toluidine into the gel of Ce(IV) phosphate in different mixing volume ratios. Effect of eluant concentration, elution behavior and pH-titration studies were carried out to understand the ion-exchange capabilities. The physico-chemical properties of the material were determined using AAS, CHN elemental analysis, UV-VIS spectrophotometry, FTIR, SEM/EDX, TGA-DTA, TEM (Transmission electron microscopy), XRD and SEM studies. The distribution studies revealed that the cation-exchange material is highly selective for Cd(II). Due to selective nature of the cation-exchanger, ion selective membrane electrode was fabricated for the determination of Cd(??) ions in solutions. The analytical utility of this electrode was established by employing it as an indicator electrode in electrometric titrations.

Khan, Asif Ali; Akhtar, Tabassum

2011-03-01

303

Automated high-pressure titration system with in situ infrared spectroscopic detection  

NASA Astrophysics Data System (ADS)

A fully automated titration system with infrared detection was developed for investigating interfacial chemistry at high pressures. The apparatus consists of a high-pressure fluid generation and delivery system coupled to a high-pressure cell with infrared optics. A manifold of electronically actuated valves is used to direct pressurized fluids into the cell. Precise reagent additions to the pressurized cell are made with calibrated tubing loops that are filled with reagent and placed in-line with the cell and a syringe pump. The cell's infrared optics facilitate both transmission and attenuated total reflection (ATR) measurements to monitor bulk-fluid composition and solid-surface phenomena such as adsorption, desorption, complexation, dissolution, and precipitation. Switching between the two measurement modes is accomplished with moveable mirrors that direct the light path of a Fourier transform infrared spectrometer into the cell along transmission or ATR light paths. The versatility of the high-pressure IR titration system was demonstrated with three case studies. First, we titrated water into supercritical CO2 (scCO2) to generate an infrared calibration curve and determine the solubility of water in CO2 at 50 °C and 90 bar. Next, we characterized the partitioning of water between a montmorillonite clay and scCO2 at 50 °C and 90 bar. Transmission-mode spectra were used to quantify changes in the clay's sorbed water concentration as a function of scCO2 hydration, and ATR measurements provided insights into competitive residency of water and CO2 on the clay surface and in the interlayer. Finally, we demonstrated how time-dependent studies can be conducted with the system by monitoring the carbonation reaction of forsterite (Mg2SiO4) in water-bearing scCO2 at 50 °C and 90 bar. Immediately after water dissolved in the scCO2, a thin film of adsorbed water formed on the mineral surface, and the film thickness increased with time as the forsterite began to dissolve. However, after approximately 2.5 h, the trend reversed, and a carbonate precipitate began to form on the forsterite surface, exposing dramatic chemical changes in the thin-water film. Collectively, these applications illustrate how the high-pressure IR titration system can provide molecular-level information about the interactions between variably wet scCO2 and minerals relevant to underground storage of CO2 (geologic carbon sequestration). The apparatus could also be utilized to study high-pressure interfacial chemistry in other areas such as catalysis, polymerization, food processing, and oil and gas recovery.

Thompson, Christopher J.; Martin, Paul F.; Chen, Jeffrey; Benezeth, Pascale; Schaef, Herbert T.; Rosso, Kevin M.; Felmy, Andrew R.; Loring, John S.

2014-04-01

304

[Model UF-2 mutant of Staphylococcus aureus 209 P for titrating Vibrio cholera enterotoxin].  

PubMed

The identical character of the action of crude V. cholerae enterotoxin on the anaerobic dehydrogenases of the UV-2 mutant of S. aureus 209 p and the surviving culture of Ehrlich's carcinoma has been revealed. The range of this action is linked with the concentration of the toxin and varies from the stimulation of cell dehydrogenases to their complete suppression. The rapid method for the titration of the enterotoxin in the dehydrogenase suppression test with the use of the bacterial model is proposed. PMID:6353817

Pasternak, N A; Ved'mina, E A; Andrusenko, I T; Shenderovich, V A; Zhuravleva, T P

1983-07-01

305

Combined ion selective electrode and fluorescence quenching detection for copper-dissolved organic matter titrations  

SciTech Connect

Copper-dissolved organic matter binding is observed for Black Lake, NC, fulvic acid by measuring free metal with a copper ion selective electrode (ISE) and the unbound organic ligand by fluorescence. The two detectors agree at low, aquatic levels of copper loading; a discrepancy at high copper concentrations may result from precipitation or inappropriate assumptions about the fluorescence technique. Complementary error properties of combined detection provide low-error titration data over a wider range of pH and pCu than either detector alone. Calibration by ISE is more reliable than curve fitting for relating fluorescence to bound copper concentrations. 24 references, 6 figures.

Cabaniss, S.E.; Shuman, M.S.

1986-02-01

306

Automated high-pressure titration system with in situ infrared spectroscopic detection.  

PubMed

A fully automated titration system with infrared detection was developed for investigating interfacial chemistry at high pressures. The apparatus consists of a high-pressure fluid generation and delivery system coupled to a high-pressure cell with infrared optics. A manifold of electronically actuated valves is used to direct pressurized fluids into the cell. Precise reagent additions to the pressurized cell are made with calibrated tubing loops that are filled with reagent and placed in-line with the cell and a syringe pump. The cell's infrared optics facilitate both transmission and attenuated total reflection (ATR) measurements to monitor bulk-fluid composition and solid-surface phenomena such as adsorption, desorption, complexation, dissolution, and precipitation. Switching between the two measurement modes is accomplished with moveable mirrors that direct the light path of a Fourier transform infrared spectrometer into the cell along transmission or ATR light paths. The versatility of the high-pressure IR titration system was demonstrated with three case studies. First, we titrated water into supercritical CO2 (scCO2) to generate an infrared calibration curve and determine the solubility of water in CO2 at 50?°C and 90 bar. Next, we characterized the partitioning of water between a montmorillonite clay and scCO2 at 50?°C and 90 bar. Transmission-mode spectra were used to quantify changes in the clay's sorbed water concentration as a function of scCO2 hydration, and ATR measurements provided insights into competitive residency of water and CO2 on the clay surface and in the interlayer. Finally, we demonstrated how time-dependent studies can be conducted with the system by monitoring the carbonation reaction of forsterite (Mg2SiO4) in water-bearing scCO2 at 50?°C and 90 bar. Immediately after water dissolved in the scCO2, a thin film of adsorbed water formed on the mineral surface, and the film thickness increased with time as the forsterite began to dissolve. However, after approximately 2.5 h, the trend reversed, and a carbonate precipitate began to form on the forsterite surface, exposing dramatic chemical changes in the thin-water film. Collectively, these applications illustrate how the high-pressure IR titration system can provide molecular-level information about the interactions between variably wet scCO2 and minerals relevant to underground storage of CO2 (geologic carbon sequestration). The apparatus could also be utilized to study high-pressure interfacial chemistry in other areas such as catalysis, polymerization, food processing, and oil and gas recovery. PMID:24784630

Thompson, Christopher J; Martin, Paul F; Chen, Jeffrey; Benezeth, Pascale; Schaef, Herbert T; Rosso, Kevin M; Felmy, Andrew R; Loring, John S

2014-04-01

307

Automated high-pressure titration system with in situ infrared spectroscopic detection  

SciTech Connect

A fully automated titration system with infrared detection was developed for investigating interfacial chemistry at high pressures. The apparatus consists of a high-pressure fluid generation and delivery system coupled to a high-pressure cell with infrared optics. A manifold of electronically actuated valves is used to direct pressurized fluids into the cell. Precise reagent additions to the pressurized cell are made with calibrated tubing loops that are filled with reagent and placed in-line with the cell and a syringe pump. The cell's infrared optics facilitate both transmission and attenuated total reflection (ATR) measurements to monitor bulk-fluid composition and solid-surface phenomena such as adsorption, desorption, complexation, dissolution, and precipitation. Switching between the two measurement modes is accomplished with moveable mirrors that direct the light path of a Fourier transform infrared spectrometer into the cell along transmission or ATR light paths. The versatility of the high-pressure IR titration system was demonstrated with three case studies. First, we titrated water into supercritical CO{sub 2} (scCO{sub 2}) to generate an infrared calibration curve and determine the solubility of water in CO{sub 2} at 50?°C and 90 bar. Next, we characterized the partitioning of water between a montmorillonite clay and scCO{sub 2} at 50?°C and 90 bar. Transmission-mode spectra were used to quantify changes in the clay's sorbed water concentration as a function of scCO{sub 2} hydration, and ATR measurements provided insights into competitive residency of water and CO{sub 2} on the clay surface and in the interlayer. Finally, we demonstrated how time-dependent studies can be conducted with the system by monitoring the carbonation reaction of forsterite (Mg{sub 2}SiO{sub 4}) in water-bearing scCO{sub 2} at 50?°C and 90 bar. Immediately after water dissolved in the scCO{sub 2}, a thin film of adsorbed water formed on the mineral surface, and the film thickness increased with time as the forsterite began to dissolve. However, after approximately 2.5 h, the trend reversed, and a carbonate precipitate began to form on the forsterite surface, exposing dramatic chemical changes in the thin-water film. Collectively, these applications illustrate how the high-pressure IR titration system can provide molecular-level information about the interactions between variably wet scCO{sub 2} and minerals relevant to underground storage of CO{sub 2} (geologic carbon sequestration). The apparatus could also be utilized to study high-pressure interfacial chemistry in other areas such as catalysis, polymerization, food processing, and oil and gas recovery.

Thompson, Christopher J., E-mail: chris.thompson@pnnl.gov; Martin, Paul F.; Chen, Jeffrey; Schaef, Herbert T.; Rosso, Kevin M.; Felmy, Andrew R.; Loring, John S. [Pacific Northwest National Laboratory, Richland, Washington 99352 (United States)] [Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Benezeth, Pascale [Géosciences Environnement Toulouse (GET), CNRS-Université de Toulouse, 31400 Toulouse (France)] [Géosciences Environnement Toulouse (GET), CNRS-Université de Toulouse, 31400 Toulouse (France)

2014-04-15

308

Automated High-Pressure Titration System with In Situ Infrared Spectroscopic Detection  

SciTech Connect

A fully automated titration system with infrared detection was developed for investigating interfacial chemistry at high pressures. The apparatus consists of a high-pressure fluid generation and delivery system coupled to a high-pressure cell with infrared optics. A manifold of electronically actuated valves is used to direct pressurized fluids into the cell. Precise reagent additions to the pressurized cell are made with calibrated tubing loops that are filled with reagent and placed in-line with the cell and a syringe pump. The cell’s infrared optics facilitate both transmission and attenuated total reflection (ATR) measurements to monitor bulk-fluid composition and solid-surface phenomena such as adsorption, desorption, complexation, dissolution, and precipitation. Switching between the two measurement modes is accomplished with moveable mirrors that direct radiation from a Fourier transform infrared spectrometer into the cell along transmission or ATR light paths. The versatility of the high-pressure IR titration system is demonstrated with three case studies. First, we titrated water into supercritical CO2 (scCO2) to generate an infrared calibration curve and determine the solubility of water in CO2 at 50 °C and 90 bar. Next, we characterized the partitioning of water between a montmorillonite clay and scCO2 at 50 °C and 90 bar. Transmission-mode spectra were used to quantify changes in the clay’s sorbed water concentration as a function of scCO2 hydration, and ATR measurements provided insights into competitive residency of water and CO2 on the clay surface and in the interlayer. Finally, we demonstrated how time-dependent studies can be conducted with the system by monitoring the carbonation reaction of forsterite (Mg2SiO4) in water-bearing scCO2 at 50 °C and 90 bar. Immediately after water dissolved in the scCO2, a thin film of adsorbed water formed on the mineral surface, and the film thickness increased with time as the forsterite began to dissolve. However, after approximately 2.5 hours, the trend reversed, and a carbonate precipitate began to form on the forsterite surface, exposing dramatic chemical changes in the thin-water film. Collectively, these applications illustrate how the high-pressure IR titration system can provide molecular-level information about the interactions between variably wet scCO2 and minerals relevant to underground storage of CO2 (geologic carbon sequestration). The apparatus could also be utilized to study high-pressure interfacial chemistry in other areas such as catalysis, polymerization, food processing, and oil and gas recovery.

Thompson, Christopher J.; Martin, Paul F.; Chen, Jeffrey; Benezeth, Pascale; Schaef, Herbert T.; Rosso, Kevin M.; Felmy, Andrew R.; Loring, John S.

2014-04-17

309

Electrochemical studies of copper and lead complexation by fulvic acid. I. Potentiometric measurements and a critical comparison of metal binding models  

Microsoft Academic Search

Copper and lead ion-selective electrodes have been used to monitor titrations of Pb and Cu with fulvic acid extracted from the River Tamar, Southwest England. The titrations were carried out in 0.1 M NaClO 4 at 25°C at pH values in the range 6.0 to 6.5. The titration data were analysed using five different models; two assuming small values of

D. R. Turner; M. S. Varney; M. Whitfield; R. F. C. Mantoura; J. P. Riley

1986-01-01

310

Cations reduce antimicrobial efficacy of lysozyme-chelator combinations.  

PubMed

Reduction of the antimicrobial efficacy of lysozyme-chelator combinations against two Escherichia coli O157:H7 strains on addition of mineral salts was studied. The objective of the study was to determine the effect of type and concentration of mono-, di-, and trivalent mineral salts on the antimicrobial effectiveness of lysozyme and various chelators against E. coli O157:H7. Seven salts (Al3+, Ca2+, Fe2+, Fe3+, K+, Mg2+, and Na+) at 1 to 10 mM were added to aqueous solutions of lysozyme and disodium ethylenediamine tetraacetic acid (EDTA), disodium pyrophosphate (DSPP), or pentasodium tripolyphosphate (PSTPP) at pH 6, 7, or 8 and applied to cultures of E. coli O157:H7 strains 932 and H1730. Inhibitory activity of lysozyme chelator combinations against both strains was completely lost after addition of > or = 1 mM Ca2+ and Mg2+ at pH 7 and 8. At pH 6, antimicrobial activity of lysozyme-EDTA against both strains was retained in the presence of calcium or magnesium cations. DSPP-lysozyme inhibited strain H1730 at pH 6 despite the presence of Mg2+. Concentrations above 4 mM Fe2+ neutralized activity of all lysozyme-chelator combinations. Reversal of inhibition by lysozyme-chelator complexes by the monovalent Na+ and K+ ions depended on E. coli O157:H7 strain type. Neither monovalent cation reversed inhibition of strain 932. However, Na+ and K+ reversed lysozyme-chelator inhibition of strain H1730. The addition of > or = 1 mM Fe3+ or Al3+ was effective in reversing inhibition of both strains by lysozyme and EDTA at pH 6, 7, and 8. Isothermal titration calorimetry was used to determine the amount of ion-specific competitive binding of free cations by EDTA-lysozyme combinations. A mechanistic model for the antimicrobial functionality of chelator-lysozyme combinations is proposed. PMID:14968960

Boland, J S; Davidson, P M; Bruce, B; Weiss, J

2004-02-01

311

A single-beam titration method for the quantification of open-path Fourier transform infrared spectroscopy  

NASA Astrophysics Data System (ADS)

This study introduced a quantitative method that can be used to measure the concentration of analytes directly from a single-beam spectrum of open-path Fourier Transform Infrared Spectroscopy (OP-FTIR). The peak shapes of the analytes in a single-beam spectrum were gradually canceled (i.e., "titrated") by dividing an aliquot of a standard transmittance spectrum with a known concentration, and the sum of the squared differential synthetic spectrum was calculated as an indicator for the end point of this titration. The quantity of a standard transmittance spectrum that is needed to reach the end point can be used to calculate the concentrations of the analytes. A NIST traceable gas standard containing six known compounds was used to compare the quantitative accuracy of both this titration method and that of a classic least square (CLS) using a closed-cell FTIR spectrum. The continuous FTIR analysis of industrial exhausting stack showed that concentration trends were consistent between the CLS and titration methods. The titration method allowed the quantification to be performed without the need of a clean single-beam background spectrum, which was beneficial for the field measurement of OP-FTIR. Persistent constituents of the atmosphere, such as NH3, CH4 and CO, were successfully quantified using the single-beam titration method with OP-FTIR data that is normally inaccurate when using the CLS method due to the lack of a suitable background spectrum. Also, the synthetic spectrum at the titration end point contained virtually no peaks of analytes, but it did contain the remaining information needed to provide an alternative means of obtaining an ideal single-beam background for OP-FTIR.

Sung, Lung-Yu; Lu, Chia-Jung

2014-09-01

312

Competitive-type displacement reaction for direct potentiometric detection of low-abundance protein.  

PubMed

Prostate-specific antigen (PSA), one of the indications of possible prostate malignancy, is used as a biomarker for the diagnosis and prognosis of prostate cancer. Herein, we develop a new homogeneous potentiometric immunoassay for sensitive detection of low-concentration PSA without the need of sample separation and washing step. Two nanostructures including positively charged polyethyleneimine-poly(styrene-co-acrylic acid) (PEI-PSAA) nanospheres and negatively charged gold nanoparticles conjugated with anti-PSA antibody (Ab-AuNP) were first synthesized by using mulsifier-free emulsion copolymerization and wet chemistry method, respectively. Thereafter, the as-prepared PEI-PSAA was used as a pseudo hapten for the construction of immunosensing probe based on an electrostatic interaction between PEI-PSAA and Ab-AuNP. Upon target introduction, the added PSA competed with PEI-PASS for Ab-AuNP based on a specific antigen-antibody interaction, and displaced Ab-AuNP from PEI-PASS. The dissociated PEI-PASS was captured through the negatively charged Nafion- modified electrode, thereby resulting in the change of membrane potential. The fabrication process was characterized by using high-resolution transmission electron microscope (HRTEM), scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDX), surface plasmon resonance (SPR) and dynamic laser scattering (DLS) technique. Under optimal conditions, the output signal was indirectly proportional to the concentration of target PSA in the sample and exhibited a dynamic range from 0.1 to 50 ng/mL with a detection limit (LOD) of 0.04 ng/mL. Intra- and inter-assay coefficients of variation (CVs) were 6.8 and 7.5%, respectively. In addition, the methodology was evaluated for analysis of 12 clinical serum samples and showed good accordance between the results obtained by the developed immunosensing protocol and a commercialized enzyme-linked immunosorbent assay (ELISA) method. PMID:24211459

Zhang, Bing; Liu, Bingqian; Chen, Guonan; Tang, Dianping

2014-03-15

313

Potentiometric Sensors Based on Surface Molecular Imprinting: Detection of Cancer Biomarkers and Viruses  

SciTech Connect

The continuing discovery of cancer biomarkers necessitates improved methods for their detection. Molecular imprinting using artificial materials provides an alternative to the detection of a wide range of substances. We applied surface molecular imprinting using self-assembled monolayers to design sensing elements for the detection of cancer biomarkers and other proteins. These elements consist of a gold-coated silicon chip onto which hydroxyl-terminated alkanethiol molecules and template biomolecule are co-adsorbed, where the thiol molecules are chemically bound to the metal substrate and self-assembled into highly ordered monolayers, the biomolecules can be removed, creating the foot-print cavities in the monolayer matrix for this kind of template molecules. Re-adsorption of the biomolecules to the sensing chip changes its potential, which can be measured potentiometrically. We applied this method to the detection of carcinoembryonic antigen (CEA) in both solutions of purified CEA and in the culture medium of a CEA-producing human colon cancer cell line. The CEA assay, validated also against a standard immunoassay, was both sensitive (detection range 2.5-250 ng/mL) and specific (no cross-reactivity with hemoglobin; no response by a non-imprinted sensor). Similar results were obtained for human amylase. In addition, we detected virions of poliovirus in a specific manner (no cross-reactivity to adenovirus, no response by a non-imprinted sensor). Our findings demonstrate the application of the principles of molecular imprinting to the development of a new method for the detection of protein cancer biomarkers and to protein-based macromolecular structures such as the capsid of a virion. This approach has the potential of generating a general assay methodology that could be highly sensitive, specific, simple and likely inexpensive.

Wang, Y.; Zhang, Z; Jain, V; Yi, J; Mueller, S; Sokolov, J; Liu, Z; Levon, K; Rigas, B; Rafailovich, M

2010-01-01

314

Potentiometric Sensor for Real-Time Monitoring of Multivalent Ion Concentrations in Molten Salt  

SciTech Connect

Electrorefining of spent metallic nuclear fuel in high temperature molten salt systems is a core technology in pyroprocessing, which in turn plays a critical role in the development of advanced fuel cycle technologies. In electrorefining, spent nuclear fuel is treated electrochemically in order to effect separations between uranium, noble metals, and active metals, which include the transuranics. The accumulation of active metals in a lithium chloride-potassium chloride (LiCl-KCl) eutectic molten salt electrolyte occurs at the expense of the UCl3-oxidant concentration in the electrolyte, which must be periodically replenished. Our interests lie with the accumulation of active metals in the molten salt electrolyte. The real-time monitoring of actinide concentrations in the molten salt electrolyte is highly desirable for controlling electrochemical operations and assuring materials control and accountancy. However, real-time monitoring is not possible with current methods for sampling and chemical analysis. A new solid-state electrochemical sensor is being developed for real-time monitoring of actinide ion concentrations in a molten salt electrorefiner. The ultimate function of the sensor is to monitor plutonium concentrations during electrorefining operations, but in this work gadolinium was employed as a surrogate material for plutonium. In a parametric study, polycrystalline sodium beta double-prime alumina (Na-ß?-alumina) discs and tubes were subject to vapor-phase exchange with gadolinium ions (Gd3+) using a gadolinium chloride salt (GdCl3) as a precursor to produce gadolinium beta double-prime alumina (Gd-ß?-alumina) samples. Electrochemical impedance spectroscopy and microstructural analysis were performed on the ion-exchanged discs to determine the relationship between ion exchange and Gd3+ ion conductivity. The ion-exchanged tubes were configured as potentiometric sensors in order to monitor real-time Gd3+ ion concentrations in mixtures of gadolinium chloride (GdCl3) in LiCl-KCl eutectic molten salts through measurement of the potential difference between a reference and working electrode.

Peter A. Zink; Jan-Fong Jue; Brenda E. Serrano; Guy L. Fredrickson; Ben F. Cowan; Steven D. Herrmann; Shelly X. Li

2010-07-01

315

Potentiometric determination of cysteine with thiol sensitive silver-mercury electrode.  

PubMed

A potentiometric procedure for cysteine thiol group concentration monitoring in media generating free radicals was developed using a thiol specific silver-mercury electrode. Electrolytic deposition of mercury on a silver wire and treatment with 20 mM cysteine in 0.5 M NaOH were used to produce the electrode. A silver-chloride electrode in saturated KCl was the reference. A glass capillary with 1 M KNO3 in 1% agarose gel was the liquid junction. The electrode responded to cysteine concentration in the range from 0.01 to 20 mM yielding a perfect linear relationship for the dependence of log [cysteine] versus electrode potential [mV], with b0 (constant) = -373.43 [mV], b1 (slope) = -53.82 and correlation coefficient r2 = 0.97. The electrode potential change per decade of cysteine concentration was 57 mV. The minimal measurable signal response was at a cysteine concentration of 0.01 mM. The signal CV amounted to 4-6% for cysteine concentrations of 0.01 to 0.05 mM and to less than 1% for cysteine concentrations of 0.5 to 20 mM. The response time ranged from about 100 s for cysteine concentrations of 0.01 to 0.1 mM to 30 s at higher cysteine concentrations. The standard curve reproducibility was the best at cysteine concentrations from 0.1 to 20 mM. In a reaction medium containing cysteine and copper(II)-histidine complex ([His-Cu]2+) solution in 55 mM phosphate buffer pH 7.4 the electrode adequately responded to changes in cysteine concentration. Beside cysteine, the silver-mercury electrode responded also to thiol groups of homocysteine and glutathione, however, the Nernst equation slope was about half of that for cysteine. PMID:17351672

Drozdz, Ryszard; Naskalski, Jerzy; Zabek-Adamska, Anna

2007-01-01

316

Polypyrrole-based potentiometric sensors: Novel devices for the detection of nitrate and urea  

SciTech Connect

Polypyrrole is a sturdy polymer with interesting structural and electronic properties that has found numerous applications in the field of Analytical Chemistry. To illustrate polypyrrole`s versatility in the development of analytical probes, two novel polypyrrole-based potentiometric sensors, one selective for nitrate (NO{sub 3}{sup -}) and the other for urea, will be described. For the nitrate selective electrode, polypyrrole was prepared electrochemically in the presence of a salt of the anion of interest. This electrochemically mediated templating approach resulted in a film that exhibited linear, near-Nernstian response to nitrate (-56 {+-} 1 mV/decade, n=18) over four decades of concentration (5.0 x 10{sup -5} - 0.50 M nitrate) and detection limits of 2 ({+-} 1) x 10{sup -5} M nitrate. The sensor exhibited improved selectivity towards nitrate in the presence of lipophilic anions like Perchlorate and iodide. The second sensor involves the use of polypyrrole as a pH-based transducer to develop a biosensor for urea. Urease was covalently attached to the surface of an amine functionalized polypyrrole film by means of a carbodiimide reaction. The resulting sensor exhibited near-Nernstian behavior to pH changes (-54 {+-} 1 mV/pH unit). The film also responded to urea with high sensitivity (93 mV/decade) and good detection limits of 1.4 x 10{sup -4} {+-} 1 x 10{sup -5} M urea (n=3). The effects on the biosensor of possible interferent species such as N-methylurea and hydroxyurea will be described.

Hernandez, E.C.; Hutchins, R.S.; Witkowski, A. [Univ. of Kentucky, Lexington, KY (United States)] [and others

1995-12-31

317

New organotin(IV) ascorbates: synthesis, spectral characterization, biological and potentiometric studies  

NASA Astrophysics Data System (ADS)

New organotin(IV) ascorbates of the general formulae R 3Sn(HAsc) (where R=Me, n-Pr, n-Bu and Ph) and R 2Sn(Asc) (where R= n-Bu and Ph) have been synthesized by the reaction of R nSnCl 4- n (where n=2 or 3) with monosodium- L-ascorbate. The bonding and coordination behaviour in these complexes are discussed on the basis of UV-Vis, IR, Far-IR, 1H and 13C NMR, and 119Sn Mössbauer spectroscopic studies. L-Ascorbic acid acts as a monoanionic bidentate ligand in R 3Sn(HAsc) coordinating through O(1) and O(3). The Mössbauer studies together with IR and NMR studies suggest that for these polymeric derivatives, the polyhedron is trigonal bipyramidal around tin with three organic groups in the equatorial positions. In R 2Sn(Asc), L-ascorbic acid acts as dianionic tetradentate ligand and a polymeric structure with octahedral geometry around tin with trans organic groups has been tentatively proposed. The complexes have been assayed for their anti-inflammatory and cardiovascular activity. Ph 2Sn(Asc) has been found to show the highest activity among the studied complexes. It is suggested on the basis of potentiometric studies of Me 2Sn(IV) and Me 3Sn(IV) systems with L-ascorbic acid that under physiological conditions (pH=7.0) Me 2Sn(HAsc)(OH) (˜60%), Me 2Sn(OH) 2 (˜40%) and Me 3Sn(HAsc) (˜60%), Me 3Sn(OH) (˜40%), respectively, are existing, which may be responsible for their biological activities.

Nath, Mala; Jairath, Ruchi; Eng, George; Song, Xueqing; Kumar, Ashok

2005-01-01

318

Potentiometric surface map of the Floridan Aquifer in the St. Johns River Water-Management District and vicinity, Florida, May 1979  

USGS Publications Warehouse

This map presents the potentiometric surface of the Floridan aquifer in the St. Johns River Water Management District and vicinity for May 1979. The Floridan aquifer is the principal source of potable water in the area. Water-level measurements were made on approximately 1200 wells and on several springs. The potentiometric surface is shown by 5-foot contour intervals except in the Fernandina Beach area where 20-foot intervals are used to show a deep cone of depression. This is the fourth map of a series covering the entire St. Johns River Water Management District and vicinity. Two maps cover the low water-level period in May and two show the high-water period in September. The potentiometric surface ranged from 125 feet above the National Vertical Datum of 1929 (NGVD) in Polk County to 120 feet below NGVD in Nassau County. (USGS)

Laughlin, Charles P.; Hayes, E.C.; Schiner, George R.

1980-01-01

319

Dopant titrating ion mobility spectrometry for trace exhaled nitric oxide detection.  

PubMed

Ion mobility spectrometry (IMS) is a promising non-invasive tool for the analysis of exhaled gas and exhaled nitric oxide (NO), a biomarker for diagnosis of respiratory diseases. However, the high moisture in exhaled gas always brings about extra overlapping ion peaks and results in poor identification ability. In this paper, p-benzoquinone (PBQ) was introduced into IMS to eliminate the interference of overlapping ion peaks and realize the selective identification of NO. The overlapping ions caused by moisture were titrated by PBQ and then converted to hydrated PBQ anions (C6H4[Formula: see text](H2O)n). The NO concentration could be determined by quantifying gas phase hydrated nitrite anions (N[Formula: see text](H2O)n), product ions of NO. Under optimized conditions, a limit of detection (LOD) of about 1.4?ppbv and a linear range of 10-200?ppbv were obtained for NO even in 100% relative humidity (RH) purified air. Furthermore, this established method was applied to measure hourly the exhaled NO of eight healthy volunteers, and real-time monitoring the exhaled NO of an esophageal carcinoma patient during radical surgery. These results revealed the potential of the current dopant titrating IMS method in the measurement of exhaled NO for medical disease diagnosis. PMID:25557839

Peng, Liying; Hua, Lei; Li, Enyou; Wang, Weiguo; Zhou, Qinghua; Wang, Xin; Wang, Changsong; Li, Jinghua; Li, Haiyang

2015-01-01

320

Correlation between ToBI test and in vivo titration for diphtheria and tetanus.  

PubMed

Alternatives to animal testing for quality control of biologicals have been a goal since 1959. Instituto Butantan has been developing such methods for quality control of biologicals for human use (vaccines and hyperimmune equine sera) for the last 13 years. In this paper we compare the modified ToBI test and the in vivo seroneutralization test to assess immunogenicity of diphtheria and tetanus vaccines and hyperimmune sera. Data from the last 10 years were statistically analyzed to compare the results for in vivo and in vitro titrations (diphtheria, n = 525 and tetanus, n = 455). The agreement between the tests depended on the serum titer range. For both diphtheria and tetanus components, the correlation and concordance coefficient was higher as the serum titer increased. Overall, the in vitro/in vivo titer ratio did not vary systematically over the range of measurements. These results indicate that although the in vitro ToBI test is not completely able to replace the in vivo serum titration, it is a useful tool to guide the tests during the production process, which can reduce the number of animals used for lot release. PMID:25458473

Quintilio, Wagner; Kapronezai, Josana; Alessandro de Freitas, Fábio

2015-01-01

321

Energetics of genome ejection from phage revealed by isothermal titration calorimetry  

NASA Astrophysics Data System (ADS)

It has been experimentally shown that ejection of double-stranded DNA from phage is driven by internal pressure reaching tens of atmospheres. This internal pressure is partially responsible for delivery of DNA into the host cell. While several theoretical models and simulations nicely describe the experimental data of internal forces either resisting active packaging or equivalently favoring spontaneous ejection, there are no direct energy measurements available that would help to verify how quantitative these theories are. We performed direct measurements of the enthalpy responsible for DNA ejection from phage ?, using Isothermal Titration Calorimetry. The phage capsids were ``opened'' in vitro by titrating ? into a solution with LamB receptor and the enthalpy of DNA ejection process was measured. In his way, enthalpy stored in ? was determined as a function of packaged DNA length comparing wild-type phage ? (48.5 kb) with a shorter ?-DNA length mutant (37.7 kb). The temperature dependence of the ejection enthalpy was also investigated. The values obtained were in good agreement with existing models and provide a better understanding of ds- DNA packaging and release mechanisms in motor-packaged viruses (e.g., tailed bacteriophages, Herpes Simplex, and adenoviruses).

Jeembaeva, Meerim; Jonsson, Bengt; Castelnovo, Martin; Evilevitch, Alex

2009-03-01

322

A novel method for the determination of the degree of deacetylation of chitosan by coulometric titration.  

PubMed

A novel method to determine the degree of deacetylation of chitosan is described. In this method, the coulometric titrant OH- is generated by the electrolysis of water. The OH- reacted with the residual hydrochloric acid in chitosan solution and the degree of deacetylation was obtained by Faraday's law. The optimized experimental parameters in this study were 1.0 mol/L KCl as supporting electrolyte, 15.00 mA as the intensity of constant current, composite glass electrode as indicating electrode couples, double platinum generated electrode-platinum wire auxiliary electrode as working electrode pairs, pH 3.80 as the titration end-point. The degree of deacetylation in the four samples, which varied from 70 to 95% were measured. The results were similar to those from 1H NMR and the standard deviations were lower than 0.5%. With merit of simplicity, convenience, quickness, high accuracy and precision, automatic detection of titration end-point and low-cost, the proposed method will be very useful in the industrial production. PMID:25020083

Wang, Chao; Yuan, Fang; Pan, Jiabao; Jiao, Shining; Jin, Ling; Cai, Hongwei

2014-09-01

323

Development of a novel baculovirus titration method using the Enzyme-linked immunosorbent spot (ELISPOT) assay.  

PubMed

The baculovirus expression vector system (BEVS) is one of the most powerful methods for production of recombinant proteins for research or commercial purposes. Titration of viable virus in insect cell culture is often required when BEVS is used for basic research or bioprocessing. An enzyme-linked immunosorbent spot (ELISPOT) assay using monoclonal antibodies against the major capsid protein VP39 of both Autographa californica nuclear polyhedrosis virus (AcMNPV) and Bombyx mori nuclear polyhedrosis virus (BmNPV) was developed for baculovirus quantitation at 48h post-infection. The titer was determined by visualizing infected insect cells as blue spots and automated spot counting was achieved with ELISPOT hardware and software. Log-scale comparison of the results between the ELISPOT assay and a conventional end point dilution assay using a fluorescent marker showed a good correlation for both AcMNPV (R(2)=0.9980, p<0.05) and BmNPV (R(2)=0.9834, p<0.05). In conclusion, a novel, rapid and semi-automated procedure for titrating baculovirus was developed based on the specific immunostaining of infected cells followed by automated spot counting. PMID:23274754

Wang, Wei; Cheng, Tong; Ma, Ke; Xia, Dezhen; Wang, Yongmei; Liu, Jian; Du, Hailian; Shih, James Wai Kuo; Zhang, Jun; Zhao, Qinjian; Xia, Ningshao

2013-03-01

324

Quantitative analysis of citric acid/sodium hypophosphite modified cotton by HPLC and conductometric titration.  

PubMed

Isocratic HPLC was used in conjunction with conductometric titration to quantitatively examine the modification of cotton cellulose by citric acid (CA)/sodium hypophosphite (SHP). CA/SHP had been extensively used as a green crosslinking agent for enhancement of cellulose and other carbohydrate polymers without in-depth understanding of the mechanisms. The current study investigated all identifiable secondary polycarboxylic acids from CA decomposition in the CA/SHP-cellulose system under various curing conditions. It was found that CA decomposition was more sensitive to temperature compared with the desirable esterification reaction. Two crosslinking mechanisms, namely ester crosslinking and SHP crosslinking were responsible for the observed improvement in crease resistance of CA/SHP treated cotton fabrics. An oligomer of citraconic acid (CCA) and/or itaconic acid (IA) was identified as a possible contributor to fabric yellowing. Finally, the crease resistance of fabrics correlated strongly with CA preservation in polyol-added CA/SHP crosslinking systems. The dosage of polyol should be held below an inflexion point to keep the undesirable competition against cellulose minimum. The combination of HPLC and conductometric titration was demonstrated to be useful in studying the CA/SHP-cellulose crosslinking system. The findings have implications for better application of CA/SHP in polysaccharide modifications in general. PMID:25659676

Ye, Tao; Wang, Bijia; Liu, Jian; Chen, Jiangang; Yang, Yiqi

2015-05-01

325

Two dinuclear Ru(II) polypyridyl complexes with different photophysical and cation recognition properties.  

PubMed

Two dinuclear Ru(II) polypyridyl complexes functionalized with vacant coordination sites have been designed and synthesized. Their photophysical properties and interactions with various metal ions have been investigated at room temperature. The two complexes exhibit different UV/Vis absorption and emission intensities. When titrated with various metal ions, complex [{Ru(bpy)2}2(?2-L(1))](4+) exhibits a notable fluorescence quenching in the presence of Cu(2+) in H2O-CH3CN media (1:1, v/v); its analogous complex [{Ru(bpy)2}2(?2-L(2))](4+) exhibits no cation selectivity, the fluorescence intensity of complex [{Ru(bpy)2}2(?2-L(2))](4+) has been enhanced by several transition metal ions due to prevention of the photo-induced electron transfer process. The fluorescence titration spectra and Benesi-Hildebrand expression reveal the formation of a 1:1 bonding mode between [{Ru(bpy)2}2(?2-L(1))](4+) and Cu(2+) ion with the association constant of 5.50×10(4) M(-1). PMID:25459607

Cheng, Feixiang; He, Chixian; Ren, Mingli; Wang, Fan; Yang, Yuting

2015-02-01

326

Two dinuclear Ru(II) polypyridyl complexes with different photophysical and cation recognition properties  

NASA Astrophysics Data System (ADS)

Two dinuclear Ru(II) polypyridyl complexes functionalized with vacant coordination sites have been designed and synthesized. Their photophysical properties and interactions with various metal ions have been investigated at room temperature. The two complexes exhibit different UV/Vis absorption and emission intensities. When titrated with various metal ions, complex [{Ru(bpy)2}2(?2-L1)]4+ exhibits a notable fluorescence quenching in the presence of Cu2+ in H2O-CH3CN media (1:1, v/v); its analogous complex [{Ru(bpy)2}2(?2-L2)]4+ exhibits no cation selectivity, the fluorescence intensity of complex [{Ru(bpy)2}2(?2-L2)]4+ has been enhanced by several transition metal ions due to prevention of the photo-induced electron transfer process. The fluorescence titration spectra and Benesi-Hildebrand expression reveal the formation of a 1:1 bonding mode between [{Ru(bpy)2}2(?2-L1)]4+ and Cu2+ ion with the association constant of 5.50 × 104 M-1.

Cheng, Feixiang; He, Chixian; Ren, Mingli; Wang, Fan; Yang, Yuting

2015-02-01

327

Heavy metal complexation by N-acyl(thio)urea-funtionalized cavitand: synthesis, extraction and potentiometric studies  

Microsoft Academic Search

The synthesis and binding properties of resorcinarene-based cavitands functionalized with N-acylthiourea moieties towards different cations are described. Extraction studies with metal (Pb2+, Cu2+, Ag+, Hg2+, Cd2+, Eu3+, Fe3+, K+, Na+, and Ca2+) picrates and the incorporation in ion selective electrodes (ISEs), show that there is more than a 40% increase of the Ag+ extraction for N-acylthiourea ionophores (2, 3, and

Marta M. Reinoso-Garcia; Willem Verboom; David N. Reinhoudt; Mariusz Pietrzak; Dorota Wojciechowska

2005-01-01

328

Heavy metal complexation by N-acyl(thio)urea-functionalized cavitands: synthesis, extraction and potentiometric studies  

Microsoft Academic Search

The synthesis and binding properties of resorcinarene-based cavitands functionalized with N-acylthiourea moieties towards different cations are described. Extraction studies with metal (Pb2+, Cu2+, Ag+, Hg2+, Cd2+, Eu3+, Fe3+, K+, Na+, and Ca2+) picrates and the incorporation in ion selective electrodes (ISEs), show that there is more than a 40% increase of the Ag+ extraction for N-acylthiourea ionophores (2, 3, and

Marta M. Reinoso García; Willem Verboom; David N. Reinhoudt; Elzbieta Malinowska; Mariusz Pietrzak; Dorota Wojciechowska

2004-01-01

329

Electronic spectra of astrophysically interesting cations  

NASA Astrophysics Data System (ADS)

The electronic spectra of polyacetylene cations were recorded at 20K in the laboratory in an ion trap instrument. These can then be compared with diffuse interstellar band (DIB) absorptions. Examination of recently published data shows that the attribution of a weak DIB at ˜506.9 nm to diacetylene cation is not justified. Study of the higher excited electronic states of polyacetylene cations shows that their widths can still be sufficiently narrow for consideration as DIB carriers.

Maier, John P.; Rice, Corey A.; Mazzotti, Fabio J.; Johnson, Anatoly

2015-01-01

330

Polyelectrolyte Condensation Induced by Linear Cations  

E-print Network

We examine the role of the condensing agent in the formation of polyelectrolyte bundles, via grand-canonical Monte Carlo simulations. Following recent experiments we use linear, rigid divalent cations of various lengths to induce condensation. Our results clarify and explain the experimental results for short cations. For longer cations we observe novel condensation behavior owing to alignment of the cations. We also study the role of the polyelectrolyte surface charge density, and find a nonmonotonic variation in bundle stability. This nonmonotonicity captures two trends that have been observed in separate experiments.

Camilo Guáqueta; Erik Luijten

2007-09-21

331

Ultrasensitive and real-time detection of proteins in blood using a potentiometric carbon-nanotube aptasensor.  

PubMed

Potentiometric sensing represents the preferred technique in many routine measurements of pH and ions. Unfortunately, the simplicity of the technique has not been exploited so far in high throughput biomolecular sensing. In this work, we demonstrate the capabilities of the hybrid functional material carbon nanotubes/aptamer for the creation of a new generation of nuclease-resistant aptasensors using the potentiometric transduction capabilities of single-walled carbon nanotubes in combination with the recognition capabilities of a protein-specific RNA aptamer. The aptasensor was used to detect and identify disease-related proteins at attomolar concentration values in a rapid and non-expensive way. The variable surface glycoprotein from African Trypanosomes was chosen as an ideal model system for a pathogenic exoantigen protein in a clinical sample. Variations in the electromotive force are achieved in real-time upon the direct addition of diluted real blood samples containing the target protein thus eliminating the need of preliminary matrix removal. This work would open the door to real-time diagnostic assays for a wide range of diseases, but also to the rapid molecular detection of several proteins in truly customizable protein biosensing platforms. PMID:23017685

Zelada-Guillén, Gustavo A; Tweed-Kent, Ailis; Niemann, Moritz; Göringer, H Ulrich; Riu, Jordi; Rius, F Xavier

2013-03-15

332

Standard addition flow method for potentiometric measurements at low concentration levels: Application to the determination of fluoride in food samples.  

PubMed

A standard addition method was implemented by using a flow manifold able to perform automatically multiple standard additions and in-line sample treatment. This analytical strategy was based on the in-line mixing of sample and standard addition solutions, using a merging zone approach. The flow system aimed to exploit the standard addition method to quantify the target analyte particularly in cases where the analyte concentration in the matrix is below the lower limit of linear response of the detector. The feasibility of the proposed flow configuration was assessed through the potentiometric determination of fluoride in sea salts of different origins and different types of coffee infusions. The limit of quantification of the proposed manifold was 5×10(-6)molL(-1), 10-fold lower than the lower limit of linear response of the potentiometric detector used. A determination rate of 8samplesh(-1) was achieved considering an experimental procedure based on three standard additions per sample. The main advantage of the proposed strategy is the simple approach to perform multiple standard additions, which can be implemented with other ion selective electrodes, especially in cases when the primary ion is below the lower limit of linear response of the detector. PMID:25435218

Galvis-Sánchez, Andrea C; Santos, João Rodrigo; Rangel, António O S S

2015-02-01

333

Miniaturized ionophore-based potentiometric sensors for the flow-injection determination of metformin in pharmaceutical formulations and biological fluids.  

PubMed

Miniaturized potentiometric sensors based on ?-cyclodextrins (?-CDs) are described for determination of metformin (Mf) in pharmaceutical preparations and biological fluids. Electrode matrix compositions are optimized on the basis of the nature and content of sensing ionophore, ionic sites and plasticizers. Coated wire electrodes (CWEs) modified with heptakis(2,3,6-tri-O-methyl)-?-CD, sodium tetrakis(4-fluorophenyl)borate (NaTFPB) and 2-fluorophenyl 2-nitrophenyl ether (f-NPE), work satisfactorily in the concentration range from 10(-6) to 10(-1) mol L(-1) with Nernstian compliance (55.7 ± 0.4 mV per decade activity) and a detection limit of 8 × 10(-7) mol L(-1). Incorporation of ?-CD as a molecular recognition element improved the electrode sensitivity and selectivity due to encapsulation of Mf into the ?-CD cavity (host-guest interaction). The developed electrodes have been successfully applied for the potentiometric determination of Mf under batch and flow injection analysis (FIA). FIA allows analysis of 90 samples per h offering the advantages of simplicity, accuracy and automation feasibility. The dissolution profile for metformin pharmaceutical samples (Cidophage®) was monitored using the proposed electrode in comparison with the official spectrophotometric methods. Characterization of the formed Mf-?-CD inclusion complexes is discussed in detail. PMID:23050261

Khaled, Elmorsy; Kamel, Manal S; Hassan, Hassan N; Abd El-Alim, Sameh H; Aboul-Enein, Hassan Y

2012-12-01

334

Potentiometric flow injection sensing system for determination of heparin based on current-controlled release of protamine.  

PubMed

A flow injection system incorporated with a polycation-sensitive polymeric membrane electrode in the flow cell is proposed for potentiometric determination of heparin. An external current in nano-ampere scale is continuously applied across the polymeric membrane for controlled release of protamine from the inner filling solution to the sample solution, which makes the electrode membrane regenerate quickly after each measurement. The protamine released at membrane-sample interface is consumed by heparin injected into the flow cell via their strong electrostatic interaction, thus decreasing the measured potential, by which heparin can be detected. Under optimized conditions, a linear relationship between the potential peak height and the concentration of heparin in the sample solution can be obtained in the range of 0.1-2.0UmL(-1), and the detection limit is 0.06UmL(-1). The proposed potentiometric sensing system has been successfully applied to the determination of heparin in undiluted sheep whole blood. PMID:25597803

Lei, Jiahong; Ding, Jiawang; Chen, Yan; Qin, Wei

2015-02-01

335

Exploiting sequential injection analysis with lab-on-valve and miniaturized potentiometric detection Epinephrine determination in pharmaceutical products.  

PubMed

Miniaturized potentiometric units were constructed, evaluated and incorporated in a SIA-LOV manifold in order to the control of pharmaceutical analysis. The method validation was done with ephinefrine determinations in commercial pharmaceutical products. The optimization procedures were directed at potential versus epinephrine concentration. This approach was achieved by selecting 60cm of reactor and a flow rate of 11muLs(-1) and injecting 78muL of epinephrine standard solutions in a 1.0x10(-3)molL(-1) IO(4)(-) solution. A linear range was found for epinephrine concentrations between 2.0x10(-4) and 2.5x10(-3)molL(-l) with a slope of 35528mVLmol(-l) and r(2)=0.997. Under these conditions the analytical results for the commercial pharmaceutical formulations of 0.908 and 0.454mgmL(-1), respectively, with a R.S.D. of 0.34 for both, was obtained. Through down scaling periodate-selective electrode it was possible to benefit from the recognized advantages of the lab-on-valve sequential-injection based systems, namely regarding equipment portability, reduced consumption of the sample and the reagents and the reduction of effluent waste. Furthermore, the new periodate electrode configuration is easy to achieve in common laboratories and enables the implementation of low volume detection cell where the electrical noise, that is frequently presented in potentiometric based procedures, is significantly reduced. PMID:19071753

Amorim, C G; Araujo, A N; Montenegro, M C B S M

2007-06-15

336

Potentiometric Surface in the Sparta-Memphis Aquifer of the Mississippi Embayment, Spring 2007  

USGS Publications Warehouse

The most widely used aquifer for industry and public supply in the Mississippi embayment in Arkansas, Louisiana, Mississippi, and Tennessee is the Sparta-Memphis aquifer. Decades of pumping from the Sparta-Memphis aquifer have affected ground-water levels throughout the Mississippi embayment. Regional assessments of water-level data from the aquifer are important to document regional water-level conditions and to develop a broad view of the effects of ground-water development and management on the sustainability and availability of the region's water supply. This information is useful to identify areas of water-level declines, identify cumulative areal declines that may cross State boundaries, evaluate the effectiveness of ground-water management strategies practiced in different States, and identify areas with substantial data gaps that may preclude effective management of ground-water resources. A ground-water flow model of the northern Mississippi embayment is being developed by the Mississippi Embayment Regional Aquifer Study (MERAS) to aid in answering questions about ground-water availability and sustainability. The MERAS study area covers parts of eight states including Alabama, Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri, and Tennessee and covers approximately 70,000 square miles. The U.S. Geological Survey (USGS) and the Mississippi Department of Environmental Quality Office of Land and Water Resources measured water levels in wells completed in the Sparta-Memphis aquifer in the spring of 2007 to assist in the MERAS model calibration and to document regional water-level conditions. Measurements by the USGS and the Mississippi Department of Environmental Quality Office of Land and Water Resources were done in cooperation with the Arkansas Natural Resources Commission; the Arkansas Geological Survey; Memphis Light, Gas and Water; Shelby County, Tennessee; and the city of Germantown, Tennessee. In 2005, total water use from the Sparta-Memphis aquifer in the Mississippi embayment was about 540 million gallons per day (Mgal/d). Water use from the Sparta-Memphis aquifer was about 170 Mgal/d in Arkansas, about 68 Mgal/d in Louisiana, about 97 Mgal/d in Mississippi, and about 205 Mgal/d in Tennessee. The author acknowledges, with great appreciation, the efforts of the personnel in the U.S. Geological Survey Water Science Centers of Arkansas, Kentucky, Louisiana, Mississippi, Missouri, and Tennessee, and the Mississippi Department of Environmental Quality Office of Land and Water Resources that participated in the planning, water-level measurement, data evaluation, and review of the potentiometric-surface map. Without the contribution of data and the technical assistance of their staffs, this report would not have been completed.

Schrader, T.P.

2008-01-01

337

Complexation of ?-cyclodextrin with a gemini surfactant studied by isothermal titration microcalorimetry and surface tensiometry.  

PubMed

We report on the inclusion complex formation of ?-cyclodextrin (?CD) with a cocogem surfactant (counterion-coupled gemini surfactant; (bis(4-(2-alkyl)benzenesulfonate)-Jeffamine salt, abbreviated as ABSJ), studied by isothermal titration calorimetry (ITC) and surface tension (SFT) measurements. We measured the critical micelle concentration (cmc) of ABSJ in water by the two experimental techniques in the temperature range 283-343 K, and determined the thermodynamic parameters of the complex formation directly by ITC and indirectly by the SFT. The stoichiometry (N), the binding constant (K), and the enthalpy of complexation were determined, and the Gibbs free energy and the entropy term were calculated from the experimental data. A novel method is presented for the determination of N and K by using surface tensiometry. PMID:24846443

Benk?, Mária; Király, László A; Puskás, Sándor; Király, Zoltán

2014-06-17

338

Universal Real-Time PCR-Based Assay for Lentiviral Titration.  

PubMed

Lentiviral vectors are efficient vehicles for stable gene transfer in both dividing and non-dividing cells. This feature among others makes lentiviral vectors a powerful tool in molecular research. However, the use of lentiviruses in research studies and clinical trials requires a precise and validated titration method. In this study, we describe a qPCR-based approach for estimation of lentiviral vector titer (pLV-THM-GFP). The use of WPRE (Woodchuck Hepatitis Virus Posttranscriptional Regulatory Element) and albumin genes as templates for an SYBR green-based real-time qPCR method allows for a rapid, sensitive, reproducible, and accurate assessment of lentiviral copy number at an integrated lentiviral DNA level. Furthermore, this optimization enables measurement of lentiviral concentration even in very poor quality and small quantity material. Consequently, this approach provides researchers with a tool to perform low-cost assessment with highly repeatable results. PMID:25370825

Barczak, Wojciech; Suchorska, Wiktoria; Rubi?, B?a?ej; Kulcenty, Katarzyna

2015-02-01

339

Thermodynamic signature of secondary nano-emulsion formation by isothermal titration calorimetry.  

PubMed

The stabilization of oil in water nano-emulsions by means of a polymer coating is extremely important; it prolongs the shelf life of the product and makes it suitable for a variety of applications ranging from nutraceutics to cosmetics and pharmaceutics. To date, an effective methodology to assess the best formulations in terms of thermodynamic stability has yet to be designed. Here, we perform a complete physicochemical characterization based on isothermal titration calorimetry (ITC) compared to conventional dynamic light scattering (DLS) to identify polymer concentration domains that are thermodynamically stable and to define the degree of stability through thermodynamic functions depending upon any relevant parameter affecting the stability itself, such as type of polymer coating, droplet distance, etc. For instance, the method was proven by measuring the energetics in the case of two different biopolymers, chitosan and poly-L-lysine, and for different concentrations of the emulsion coated with poly-L-lysine. PMID:25396753

Fotticchia, Iolanda; Fotticchia, Teresa; Mattia, Carlo Andrea; Netti, Paolo Antonio; Vecchione, Raffaele; Giancola, Concetta

2014-12-01

340

Applications of Isothermal Titration Calorimetry in Biophysical Studies of G-quadruplexes  

PubMed Central

G-quadruplexes are higher-order nucleic acids structures formed by G-rich sequences that are stabilized by tetrads of hydrogen-bonded guanine bases. Recently, there has been growing interest in the study of G-quadruplexes because of their possible involvement in many biological processes. Isothermal titration calorimetry (ITC) has been proven to be a useful tool to study the energetic aspects of G-quadruplex interactions. Particularly, ITC has been applied many times to determine the thermodynamic properties of drug-quadruplex interactions to screening among various drugs and to address drug design. In the present review, we will focus on the ITC studies of G-quadruplex structures and their interaction with proteins and drugs and the most significant results will be discussed. PMID:19742177

Pagano, Bruno; Mattia, Carlo Andrea; Giancola, Concetta

2009-01-01

341

DNA heats up : Energetics of genome ejection from phage revealed by isothermal titration calorimetry  

E-print Network

Most bacteriophages are known to inject their double-stranded DNA into bacteria upon receptor binding in an essentially spontaneous way. This downhill thermodynamic process from the intact virion toward the empty viral capsid plus released DNA is made possible by the energy stored during active packaging of the genome into the capsid. Only indirect measurements of this energy have been available until now using either single-molecule or osmotic suppression techniques. In this paper, we describe for the first time the use of isothermal titration calorimetry to directly measure the heat released (or equivalently the enthalpy) during DNA ejection from phage lambda, triggered in solution by a solubilized receptor. Quantitative analyses of the results lead to the identification of thermodynamic determinants associated with DNA ejection. The values obtained were found to be consistent with those previously predicted by analytical models and numerical simulations. Moreover, the results confirm the role of DNA hydration in the energetics of genome confinement in viral capsids.

Meerim Jeembaeva; B. Jönsson; Martin Castelnovo; Alex Evilevitch

2010-01-06

342

Automatic technique for simultaneous H 2 and H 2O titration in MOX fuels  

NASA Astrophysics Data System (ADS)

A new and direct automatic method has been developed to measure the residual H 2 content of MOX fuel to be irradiated in a PWR. The sources of hydrogen in the pellets are either free hydrogen or moisture and can play an important role in the possible in-pile corrosion of the zircaloy cladding. The method is based on the simultaneous determinations of water with an hygrometrie probe and of hydrogen by a thermal conductivity cell and allows an original check of the two impurities concentrations. The entire set-up is fully computerized (weighing, titrating and display of results) and leads to an accuracy better than 0.1 ?gH2/ g ( U, Pu) O2 which fits the required PWR specification.

Bonnerot, J. M.; Warin, D.

1991-02-01

343

Heats of Mixing Using an Isothermal Titration Calorimeter: Associated Thermal Effects  

PubMed Central

The correct determination of the energy generated or absorbed in the sample cell of an Isothermal Titration Calorimeter (ITC) requires a thorough analysis of the calorimetric signal. This means the identification and quantification of any thermal effect inherent to the working method. In this work, it is carried out a review on several thermal effects, studied by us in previous work, and which appear when an ITC is used for measuring the heats of mixing of liquids in a continuous mode. These effects are due to: (i) the difference between the temperature of the injected liquid and the temperature of the mixture during the mixing process, (ii) the increase of the liquid volume located in the mixing cell and (iii) the stirring velocity. Besides, methods for the identification and quantification of the mentioned effects are suggested. PMID:19742175

de Rivera, Manuel Rodríguez; Socorro, Fabiola; Matos, José S.

2009-01-01

344

Titration biosensors for the estimation of the biochemical nitrate demand of municipal and industrial wastes.  

PubMed

An anoxic titrimetric test was investigated for measuring denitrification potential of different wastewaters, both municipal and industrial, and to quantify the denitrifying activity in an activated sludge system. The method measures the amount of acid that is required to maintain the pH set-point value in a batch denitrification experiment, and it was performed using a DENICON (denitrification controller) biosensor. The amount of acid is proportional to the nitrate used to oxidise the biodegradable chemical oxygen demand present in the wastewater, while the acid consumption rate is used to derive the denitrifying activity. The wastewaters tested were a municipal wastewater (MW), an industrial-municipal wastewater (MIW; 70% and 30%, respectively), and four industrial wastewaters drawn from an ice-cream factory (IW1), a beet-sugar factory (IW2), a brewery (IW3), and a tuna cannery industry (IW4). Good correlation between titration data and analyses was found. PMID:15856352

Onnis, A; Carucci, A; Cappai, G

2006-03-01

345

High concentration aqueous sodium fluoride certified reference materials for forensic use certified by complexometric titration.  

PubMed

Sodium fluoride in concentrations of 1 to 2 % is used to prevent the formation of ethanol in blood and urine samples that are to be analysed for ethanol content. The majority of such samples form part of forensic investigations into alleged drunken driving. In South Africa, the laboratory performing the tests is required to prove that the sodium fluoride concentration in the blood samples is above 1 g/100 ml on receipt. This is done by using a fluoride ion-selective electrode calibrated with external aqueous solutions of sodium fluoride. The National Metrology Institute of South Africa (NMISA) prepares sodium fluoride solutions in concentrations from 0.3 to 3.0 g/100 ml. No other certified sodium fluoride reference solutions in these concentrations are available commercially. The sodium fluoride is certified by precipitation of the fluoride as lead chlorofluoride (PbClF) through the addition of a known excess of lead nitrate. The excess lead is back-titrated with ethylenediamine tetraacetic acid (EDTA) using a photometric electrode to detect the endpoint. Aqueous sodium fluoride solutions are prepared and the concentrations verified by the precipitation/back-titration method. This paper shows the application of a classical complexometric method to the certification of reference materials and describes the procedures for the preparation of the sodium fluoride solutions, verification of the concentrations, homogeneity and stability by primary titrimetry. It also briefly covers the calculation of uncertainty, the establishment of traceability and the quality control measures applied to ensure the quality of the certified reference materials (CRMs). PMID:25326884

Archer, Marcellé; Brits, Martin; Prevoo-Franzsen, Désirée; Quinn, Laura

2014-10-19

346

Cation-coupled bicarbonate transporters.  

PubMed

Cation-coupled HCO3(-) transport was initially identified in the mid-1970s when pioneering studies showed that acid extrusion from cells is stimulated by CO2/HCO3(-) and associated with Na(+) and Cl(-) movement. The first Na(+)-coupled bicarbonate transporter (NCBT) was expression-cloned in the late 1990s. There are currently five mammalian NCBTs in the SLC4-family: the electrogenic Na,HCO3-cotransporters NBCe1 and NBCe2 (SLC4A4 and SLC4A5 gene products); the electroneutral Na,HCO3-cotransporter NBCn1 (SLC4A7 gene product); the Na(+)-driven Cl,HCO3-exchanger NDCBE (SLC4A8 gene product); and NBCn2/NCBE (SLC4A10 gene product), which has been characterized as an electroneutral Na,HCO3-cotransporter or a Na(+)-driven Cl,HCO3-exchanger. Despite the similarity in amino acid sequence and predicted structure among the NCBTs of the SLC4-family, they exhibit distinct differences in ion dependency, transport function, pharmacological properties, and interactions with other proteins. In epithelia, NCBTs are involved in transcellular movement of acid-base equivalents and intracellular pH control. In nonepithelial tissues, NCBTs contribute to intracellular pH regulation; and hence, they are crucial for diverse tissue functions including neuronal discharge, sensory neuron development, performance of the heart, and vascular tone regulation. The function and expression levels of the NCBTs are generally sensitive to intracellular and systemic pH. Animal models have revealed pathophysiological roles of the transporters in disease states including metabolic acidosis, hypertension, visual defects, and epileptic seizures. Studies are being conducted to understand the physiological consequences of genetic polymorphisms in the SLC4-members, which are associated with cancer, hypertension, and drug addiction. Here, we describe the current knowledge regarding the function, structure, and regulation of the mammalian cation-coupled HCO3(-) transporters of the SLC4-family. PMID:25428855

Aalkjaer, Christian; Boedtkjer, Ebbe; Choi, Inyeong; Lee, Soojung

2014-10-01

347

Tobermorites: A New Family of Cation Exchangers  

Microsoft Academic Search

Tobermorites have cation-exchange and selectivity properties intermediate between those of clay minerals and zeolites. Aluminum-substituted tobermorites in particular show high selectivity for cesium. This new group of cation exchangers may find applications in catalysis and in nuclear and hazardous waste disposal.

Sridhar Komarneni; Della M. Roy

1983-01-01

348

Interlayer cation exchange stabilizes polar perovskite surfaces.  

PubMed

Global optimization is used to study the structure of the polar KTaO3 (001) surface. It is found that cation exchange near the surface leads to the most stable structure. This mechanism is likely to be general to metal oxides containing cations of differing charge. PMID:25196987

Deacon-Smith, Daniel E E; Scanlon, David O; Catlow, C Richard A; Sokol, Alexey A; Woodley, Scott M

2014-11-01

349

Effects of Organic and Inorganic Polyamine Cations  

E-print Network

of spermine, spermidine, putrescine, and cobalt [Co(III)]­hexamine cations on the solution structure of HSA cation: spermine Co(III)­hexamine spermidine putrescine. The overall binding constants are 1.7 104 , 1 of the interaction of HSA with sperm- ine, spermidine, putrescine, and cobalt­hexamine cat- ions with the following

Carpentier, Robert

350

The ?-Cation Radical of Chlorophyll a*  

PubMed Central

Chlorophyll a undergoes reversible one-electron oxidation in dichloromethane and butyronitrile. Removal of the electron by controlled potential electrolysis or by stoichiometric charge transfer to a known cation radical yields a radical (epr line width = 9 gauss, g = 2.0025 ± 0.0001) whose optical spectrum is bleached relative to that of chlorophyll. Upon electrophoresis this bleached species behaves as a cation. By comparison with the known properties of ?-cation radicals of porphyrins and chlorins, the chlorophyll radical is also identified as a ?-cation. Further correlation of optical and epr properties with published studies on photosynthesis leads to the conclusion that oxidized P700, the first photochemical product of photosystem I in green plants, contains a ?-cation radical of the chlorin component of chlorophyll a. This radical is the likely source of the rapidly-decaying, narrow epr signal of photosynthesis. PMID:16591873

Borg, Donald C.; Fajer, Jack; Felton, Ronald H.; Dolphin, David

1970-01-01

351

Creating a monthly time series of the potentiometric surface in the Upper Floridan aquifer, Northern Tampa Bay area, Florida, January 2000-December 2009  

USGS Publications Warehouse

In Florida’s karst terrain, where groundwater and surface waters interact, a mapping time series of the potentiometric surface in the Upper Floridan aquifer offers a versatile metric for assessing the hydrologic condition of both the aquifer and overlying streams and wetlands. Long-term groundwater monitoring data were used to generate a monthly time series of potentiometric surfaces in the Upper Floridan aquifer over a 573-square-mile area of west-central Florida between January 2000 and December 2009. Recorded groundwater elevations were collated for 260 groundwater monitoring wells in the Northern Tampa Bay area, and a continuous time series of daily observations was created for 197 of the wells by estimating missing daily values through regression relations with other monitoring wells. Kriging was used to interpolate the monthly average potentiometric-surface elevation in the Upper Floridan aquifer over a decade. The mapping time series gives spatial and temporal coherence to groundwater monitoring data collected continuously over the decade by three different organizations, but at various frequencies. Further, the mapping time series describes the potentiometric surface beneath parts of six regionally important stream watersheds and 11 municipal well fields that collectively withdraw about 90 million gallons per day from the Upper Floridan aquifer. Monthly semivariogram models were developed using monthly average groundwater levels at wells. Kriging was used to interpolate the monthly average potentiometric-surface elevations and to quantify the uncertainty in the interpolated elevations. Drawdown of the potentiometric surface within well fields was likely the cause of a characteristic decrease and then increase in the observed semivariance with increasing lag distance. This characteristic made use of the hole effect model appropriate for describing the monthly semivariograms and the interpolated surfaces. Spatial variance reflected in the monthly semivariograms decreased markedly between 2002 and 2003, timing that coincided with decreases in well-field pumping. Cross-validation results suggest that the kriging interpolation may smooth over the drawdown of the potentiometric surface near production wells. The groundwater monitoring network of 197 wells yielded an average kriging error in the potentiometric-surface elevations of 2 feet or less over approximately 70 percent of the map area. Additional data collection within the existing monitoring network of 260 wells and near selected well fields could reduce the error in individual months. Reducing the kriging error in other areas would require adding new monitoring wells. Potentiometric-surface elevations fluctuated by as much as 30 feet over the study period, and the spatially averaged elevation for the entire surface rose by about 2 feet over the decade. Monthly potentiometric-surface elevations describe the lateral groundwater flow patterns in the aquifer and are usable at a variety of spatial scales to describe vertical groundwater recharge and discharge conditions for overlying surface-water features.

Lee, Terrie M.; Fouad, Geoffrey G.

2014-01-01

352

Reference method for total water in lint cotton by automated oven drying combined with volumetric Karl Fischer titration  

Technology Transfer Automated Retrieval System (TEKTRAN)

In a preliminary study to measure total water in lint cotton we demonstrated that volumetric Karl Fischer Titration of moisture transported by a carrier gas from an attached small oven is more accurate than standard oven drying in air. The objective of the present study was to assess the measuremen...

353

A rapid Q-PCR titration protocol for adenovirus and helper-dependent adenovirus vectors that produces biologically relevant results  

PubMed Central

Adenoviruses are employed in the study of cellular processes and as expression vectors used in gene therapy. The success and reproducibility of these studies is dependent in part on having accurate and meaningful titers of replication competent and helper-dependent adenovirus stocks, which is problematic due to the use of varied and divergent titration protocols. Physical titration methods, which quantify the total number of viral particles, are used by many, but are poor at estimating activity. Biological titration methods, such as plaque assays, are more biologically relevant, but are time consuming and not applicable to helper-dependent gene therapy vectors. To address this, a protocol was developed called “infectious genome titration” in which viral DNA is isolated from the nuclei of cells ~3 h post-infection, and then quantified by Q-PCR. This approach ensures that only biologically active virions are counted as part of the titer determination. This approach is rapid, robust, sensitive, reproducible, and applicable to all forms of adenovirus. Unlike other Q-PCR-based methods, titers determined by this protocol are well correlated with biological activity. PMID:23624118

Gallaher, Sean D.; Berk, Arnold J.

2013-01-01

354

A rapid Q-PCR titration protocol for adenovirus and helper-dependent adenovirus vectors that produces biologically relevant results.  

PubMed

Adenoviruses are employed in the study of cellular processes and as expression vectors used in gene therapy. The success and reproducibility of these studies is dependent in part on having accurate and meaningful titers of replication competent and helper-dependent adenovirus stocks, which is problematic due to the use of varied and divergent titration protocols. Physical titration methods, which quantify the total number of viral particles, are used by many, but are poor at estimating activity. Biological titration methods, such as plaque assays, are more biologically relevant, but are time consuming and not applicable to helper-dependent gene therapy vectors. To address this, a protocol was developed called "infectious genome titration" in which viral DNA is isolated from the nuclei of cells ~3 h post-infection, and then quantified by Q-PCR. This approach ensures that only biologically active virions are counted as part of the titer determination. This approach is rapid, robust, sensitive, reproducible, and applicable to all forms of adenovirus. Unlike other Q-PCR-based methods, titers determined by this protocol are well correlated with biological activity. PMID:23624118

Gallaher, Sean D; Berk, Arnold J

2013-09-01

355

Anal. Chem. 1982, 54, 2117-2120 2117 validity of the ASV titration method. We are confident that  

E-print Network

Anal. Chem. 1982, 54, 2117-2120 2117 validity of the ASV titration method. We are confident. H. Anal. Chem.,preceding paper in this issue. Tuschall, J. R., Jr.; Brezonik, P. L. Anal. Chem. 1981, 53, 1986-1989. Shuman, M. S. Anal. Chem. 1982, 54, 998-1000. Brezonlk, P. L; Tuschall, J. R., Jr

Zare, Richard N.

356

Reference test methods for total water in lint cotton by Karl Fischer Titration and low temperature distillation  

Technology Transfer Automated Retrieval System (TEKTRAN)

In a study of comparability of total water contents (%) of conditioned cottons by Karl Fischer Titration (KFT) and Low Temperature Distillation (LTD) reference methods, we demonstrated a match of averaged results based on a large number of replications and weighing the test specimens at the same tim...

357

Speci cation and Veri cation of a Steam-Boiler with Signal-Coq Micka l Kerb uf1  

E-print Network

Speci cation and Veri cation of a Steam-Boiler with Signal-Coq Micka l Kerb uf1 , David Nowak2 assistant, Coq, for the speci cation and the veri cation of co-inductive properties of the well-known steam-boiler cation tools. Keywords: synchronous programming, theorem proving, the steam- boiler problem. 1

Boyer, Edmond

358

Infrared Spectroscopy of the Mass 43 Cation: Acetyl Cation and Protonated Ketene  

NASA Astrophysics Data System (ADS)

The mass 43 cation [C_2,H_3,O]^+ is prominent in mass spectra of organic molecules. Theory predicts no less than nine structural isomers, and the acetyl cation CH_3CO^+ is the global minimum. The infrared spectrum of the mass 43 cation from methyl acetate shows vibrations only from the acetyl cation. The effects of the methyl free internal rotor are discussed. The mass 43 cation from acetone shows evidence for both the acetyl cation and the less thermodynamically stable ( 50 kcal/mol) protonated ketene isomer CH_2COH^+. The effects of varying the kinetic trapping conditions in our ion source on isomeric ratios of the mass 43 cation are discussed.

Mosley, Jonathan D.; Duncan, Michael A.

2013-06-01

359

Clinical outcomes during opioid titration following initiation with or conversion to Remoxy®, an extended-release formulation of oxycodone.  

PubMed

Intra- and interpatient variability in opioid response usually necessitates opioid therapy titration to optimally balance analgesia and side effects, whether initiating therapy or converting from another opioid. Remoxy® (King Pharmaceuticals, Inc., Bristol, TN, which was acquired by Pfizer Inc in March 2011) is an extended-release formulation of oxycodone designed to maintain its rate-controlling mechanism following physical and chemical manipulation. A recent phase 3 trial, which required dose titration following initiation or conversion to Remoxy, demonstrated the long-term safety and efficacy of Remoxy in relieving moderate to severe chronic pain. In this study, opioid-naïve patients were to be initiated on Remoxy 5 mg twice daily (10 mg total daily oxycodone dose) and opioid-experienced patients were to be converted to Remoxy at a dose equivalent to their previous opioid daily dose, determined from a conversion chart. A post-hoc analysis of study data provided clinically relevant information regarding initiation of or conversion to Remoxy. The intent-to-treat population (N=823) consisted of 429 opioid-experienced patients (52%) and 394 opioid-naïve patients (48%). A stable Remoxy dose (defined as the first dose administered on 2 consecutive visits, whereby on the first of these visits, further dose titration was deemed unnecessary) was achieved by 325 opioid-experienced patients (76%; mean, 2.2 titration steps), of whom 278 (86%) successfully converted to Remoxy according to the prospectively determined post-hoc definition (?4 titration steps). Of opioid-naïve patients, 300 (76%) reached a stable dose of Remoxy (mean, 2.2 titration steps), 253 (84%) of whom successfully initiated on Remoxy. Pain intensity decreased from baseline to study completion by approximately 35% for both opioid-experienced and opioid-naïve patients and adverse events were similar to those typically reported for opioids, with a higher incidence rate reported during titration (pre-stable dose period). These data provide important clinical information when initiating opioid-naïve patients on or converting opioid-experienced patients to Remoxy. PMID:21680999

Roland, Carl L; Setnik, Beatrice; Cleveland, Jody M; Brown, David A

2011-07-01

360

Electrophoretic separation of alginic sodium diester and sodium hexametaphosphate in chondroitin sulfate that interfere with the cetylpyridinium chloride titration assay.  

PubMed

The most commonly used chondroitin sulfate (CS) assay method is cetylpyridinium chloride (CPC) titration. Cellulose acetate membrane electrophoresis (CAME) is the technique used for detection of impurities in the U.S. Pharmacopeia's CS monograph. Because CPC titration is a relatively nonspecific quantitative technique, the apparent amount of CS as determined by CPC titration alone may not reflect the true amount of CS due to possible interference with the CPC assay by impurities that contain CPC titratable functional groups. When CAME is used in conjunction with CPC titration, certain non-CS and adulterants can be visualized and estimated, and a true value for CS can be assigned once the presence of these non-CS impurities has been ruled out. This study examines conjunct application of CPC and CAME in ascertaining CS assay and purity in the presence of certain adulterants. These include propylene glycol alginate sulfate sodium, known in commerce as alginic sodium diester (ASD), and Zero One (Z1), a water-soluble agent newly reported in the CS marketplace and subsequently identified as sodium hexametaphosphate. ASD, Z1, and CS are similar in physical appearance and solubility in water and ethanol. They are also titratable anions and form ionic pairs with CPC, therefore interfering with the CPC titration assay for CS CAME separates these adulterants from each other and from CS by differences in their electrophoretic mobility. CAME is able to detect these impurities in CS at levels as low as 0.66% by weight. Although it is recommended that a method for detecting impurities (e.g., CAME) be used in cormbination with relatively nonspecific assay methods such as CPC titration, this is seldom done in practice. Assay results for CS derived fromn CPC titration may, therefore, be misleading, leaving the CS supply chain vulnerable to adulteration. In this study, the authors investigated ASD and Z1 adulteration of CS and developed an electrophoretic separation of these adulterants in CS and procedures to isolate ASD from CS matrixes containing these adulterants. The authors describe in this paper utilization of an orthogonal approach to establish the identity of Z1 as sodium hexametaphosphate and to confirm the identity of ASD, including ethanol fractionation, FTIR spectroscopy, differential scanning calorimetry, and NMR spectroscopy. The authors suggest that CAME is a cost-effective and easy to use methodfor detecting certain impurities in CS raw ingredients and recommend that CPC and CAME be used in combination by QC laboratories as a means of effectively deterring the practice of adulterating CS raw materials with the known adulterants ASD and Z1 and/or other non-chondroitin substances that can be separated from CSby CAME and that exhibit CPC titration behavior similar to CS. PMID:25372663

Weiguo, Zhang; Giancaspro, Gabriel; Adams, Kristie M; Neal-Kababick, James; Hildreth, Jana; Li, Aishan; Roman, Mark C; Betz, Joseph M

2014-01-01

361

A simple method to prepare magnetic modified beer yeast and its application for cationic dye adsorption.  

PubMed

The purpose of this research is to use a simple method to prepare magnetic modified biomass with good adsorption performances for cationic ions. The magnetic modified biomass was prepared by two steps: (1) preparation of pyromellitic dianhydride (PMDA) modified biomass in N, N-dimethylacetamide solution and (2) preparation of magnetic PMDA modified biomass by a situ co-precipitation method under the assistance of ultrasound irradiation in ammonia water. The adsorption potential of the as-prepared magnetic modified biomass was analyzed by using cationic dyes: methylene blue and basic magenta as model dyes. Optical micrograph and x-ray diffraction analyses showed that Fe(3)O(4) particles were precipitated on the modified biomass surface. The as-prepared biosorbent could be recycled easily by using an applied magnetic field. Titration analysis showed that the total concentration of the functional groups on the magnetic PMDA modified biomass was calculated to be 0.75 mmol g(-1) by using the first derivative method. The adsorption capacities (q(m)) of the magnetic PMDA modified biomass for methylene blue and basic magenta were 609.0 and 520.9 mg g(-1), respectively, according to the Langmuir equation. Kinetics experiment showed that adsorption could be completed within 150 min for both dyes. The desorption experiment showed that the magnetic sorbent could be used repeatedly after regeneration. The as-prepared magnetic modified sorbent had a potential in the dyeing industry wastewater treatment. PMID:22529003

Yu, Jun-Xia; Wang, Li-Yan; Chi, Ru-An; Zhang, Yue-Fei; Xu, Zhi-Gao; Guo, Jia

2013-01-01

362

Rapid automated method for on-site determination of sulfadiazine in fish farming: a stainless steel veterinary syringe coated with a selective membrane of PVC serving as a potentiometric detector in a flow-injection-analysis system.  

PubMed

Sulfadiazine is an antibiotic of the sulfonamide group and is used as a veterinary drug in fish farming. Monitoring it in the tanks is fundamental to control the applied doses and avoid environmental dissemination. Pursuing this goal, we included a novel potentiometric design in a flow-injection assembly. The electrode body was a stainless steel needle veterinary syringe of 0.8-mm inner diameter. A selective membrane of PVC acted as a sensory surface. Its composition, the length of the electrode, and other flow variables were optimized. The best performance was obtained for sensors of 1.5-cm length and a membrane composition of 33% PVC, 66% o-nitrophenyloctyl ether, 1% ion exchanger, and a small amount of a cationic additive. It exhibited Nernstian slopes of 61.0 mV decade(-1) down to 1.0 × 10(-5) mol L(-1), with a limit of detection of 3.1 × 10(-6) mol L(-1) in flowing media. All necessary pH/ionic strength adjustments were performed online by merging the sample plug with a buffer carrier of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, pH 4.9. The sensor exhibited the advantages of a fast response time (less than 15 s), long operational lifetime (60 days), and good selectivity for chloride, nitrite, acetate, tartrate, citrate, and ascorbate. The flow setup was successfully applied to the analysis of aquaculture waters. The analytical results were validated against those obtained with liquid chromatography-tandem mass spectrometry procedures. The sampling rate was about 84 samples per hour and recoveries ranged from 95.9 to 106.9%. PMID:21993912

Almeida, S A A; Amorim, L R; Heitor, A H; Montenegro, M C B S M; Barbosa, J; Sá, L C; Sales, M G F

2011-12-01

363

Cation-? interactions in protonated phenylalkylamines.  

PubMed

Phenylalkylamines of the general formula C6H5(CH2)nNH2 (n = 1-4) have been delivered to the gas phase as protonated species using electrospray ionization. The ions thus formed have been assayed by IRMPD spectroscopy in two different spectroscopic domains, namely, the 600-1800 and the 3000-3500 cm(-1) regions using either an IR free electron laser or a tabletop OPO/OPA laser source. The interpretation of the experimental spectra is aided by density functional theory calculations of candidate species and vibrational frequency analyses. Protonated benzylamine presents a relatively straightforward instance of a single stable conformer, providing a trial case for the adopted approach. Turning to the higher homologues, C6H5(CH2)nNH3(+) (n = 2-4), more conformations become accessible. For each C6H5(CH2)nNH3(+) ion (n = 2-4), the most stable geometry is characterized by cation-? interactions between the positively charged ammonium group and the aromatic ?-electronic system, permitted by the folding of the polymethylene chain. The IRMPD spectra of the sampled ions confirm the presence of the folded structures by comparison with the calculated IR spectra of the various possible conformers. An inspection of the NH stretching region is helpful in this regard. PMID:25061749

Chiavarino, Barbara; Crestoni, Maria Elisa; Schütz, Markus; Bouchet, Aude; Piccirillo, Susanna; Steinmetz, Vincent; Dopfer, Otto; Fornarini, Simonetta

2014-08-28

364

Measurement of atmospheric OH by titration of near-IR fluorescent dyes  

NASA Technical Reports Server (NTRS)

Recent research has shown that certain polymethine dyes can be detected at ultratrace levels (greater than or equal to 6x10(exp -14) M) in solution by fluorimetry. These detection limits are possible because of the inherent sensitivity of fluorescence techniques, because the dyes fluoresce in the near infrared region where background interference is negligible, and because powerful infrared diode lasers are now available to improve the signal to noise ratio. Other work has shown that the hydroxyl radical destroys the ability of polymethine dyes to fluoresce. These observations form the basis for a new hydroxyl radical detector that is essentially a fluorometric titrator. Theoretically, the detector should show an acceptable sensitivity and response time. Assuming that the atmospheric HO concentration is about 10(exp -11) moles m(exp -3) (i.e. 10(exp 6) molecules cm(exp -3)), then 10 L of air 'titrated' with 20 mL of 10(exp -11) M dye solution (an easily detected concentration) should result in a drop in the fluorescent signal of 50 percent - a readily detectable change. At a flow rate of 3 L min(exp -1) the sampling time would be 3 minutes. The biggest potential problem is selectivity: other oxidants may also cause the fluorescence signal to be lost. The chemistry of polymethine dyes has not been studied in detail and so no quantitative data are available. However, a survey of the literature suggests that in general HO should react up to six orders of magnitude faster than HO2 and other radicals such as RO2 and RO. It should also react much more rapidly than H2O2 and O3. Thus it may be possible to discriminate kinetically against potential interfering substances. It was shown in the laboratory that 10(exp -4) M H2O2 has little effect on the absorption spectrum of the dye IR125 over a period of hours but that the band at 780 nm is slowly lost in water over a period of days even under argon in the dark. By contrast, DMSO solutions of IR125 are stable.

Betterton, Eric A.; Gast, Karl

1994-01-01

365

A titration approach to identify the capacity for starch digestion in milk-fed calves.  

PubMed

Calf milk replacers (MR) commonly contain 40% to 50% lactose. For economic reasons, starch is of interest as a lactose replacer. Compared with lactose, starch digestion is generally low in calves. It is, however, unknown which enzyme limits the rate of starch digestion. The objectives were to determine which enzyme limits starch digestion and to assess the maximum capacity for starch digestion in milk-fed calves. A within-animal titration study was performed, where lactose was exchanged stepwise for one of four starch products (SP). The four corn-based SP differed in size and branching, therefore requiring different ratios of starch-degrading enzymes for their complete hydrolysis to glucose: gelatinised starch (?-amylase and (iso)maltase); maltodextrin ((iso)maltase and ?-amylase); maltodextrin with ?-1,6-branching (isomaltase, maltase and ?-amylase) and maltose (maltase). When exceeding the animal's capacity to enzymatically hydrolyse starch, fermentation occurs, leading to a reduced faecal dry matter (DM) content and pH. Forty calves (13 weeks of age) were assigned to either a lactose control diet or one of four titration strategies (n=8 per treatment), each testing the stepwise exchange of lactose for one SP. Dietary inclusion of each SP was increased weekly by 3% at the expense of lactose and faecal samples were collected from the rectum weekly to determine DM content and pH. The increase in SP inclusion was stopped when faecal DM content dropped below 10.6% (i.e. 75% of the average initial faecal DM content) for 3 consecutive weeks. For control calves, faecal DM content and pH did not change over time. For 87% of the SP-fed calves, faecal DM and pH decreased already at low inclusion levels, and linear regression provided a better fit of the data (faecal DM content or pH v. time) than non-linear regression. For all SP treatments, faecal DM content and pH decreased in time (P<0.001) and slopes for faecal DM content and pH in time differed from CON; P<0.001 for all SP), but did not differ between SP treatments. Faecal DM content of SP-fed calves decreased by 0.57% and faecal pH by 0.32 per week. In conclusion, faecal DM content and pH sensitively respond to incremental inclusion of SP in calf MR, independently of SP characteristics. All SP require maltase to achieve complete hydrolysis to glucose. We therefore suggest that maltase activity limits starch digestion and that fermentation may contribute substantially to total tract starch disappearance in milk-fed calves. PMID:25205419

Gilbert, M S; van den Borne, J J G C; Berends, H; Pantophlet, A J; Schols, H A; Gerrits, W J J

2015-02-01

366

Planar Zeolite Film-Based Potentiometric Gas Sensors Manufactured by a Combined Thick-Film and Electroplating Technique  

PubMed Central

Zeolites are promising materials in the field of gas sensors. In this technology-oriented paper, a planar setup for potentiometric hydrocarbon and hydrogen gas sensors using zeolites as ionic sodium conductors is presented, in which the Pt-loaded Na-ZSM-5 zeolite is applied using a thick-film technique between two interdigitated gold electrodes and one of them is selectively covered for the first time by an electroplated chromium oxide film. The influence of the sensor temperature, the type of hydrocarbons, the zeolite film thickness, and the chromium oxide film thickness is investigated. The influence of the zeolite on the sensor response is briefly discussed in the light of studies dealing with zeolites as selectivity-enhancing cover layers. PMID:22164042

Marr, Isabella; Reiß, Sebastian; Hagen, Gunter; Moos, Ralf

2011-01-01

367

Humidity response properties of a potentiometric sensor using LaF3 thin film as the solid electrolyte.  

PubMed

A thin-film type potentiometric sensor has been prepared by the implementation of electro-beam evaporation, rf magnetron sputtering methods, and micromachining processes. Sn film was deposited on n-Si/SiO(2) (400 nm) substrate. A deposited LaF(3) film was applied as solid electrolyte and sputtered Pt film was used as the sensing electrode. The patterns of the Pt and LaF(3) were realized by the micromachining processes. The LaF(3) film was characterized by scanning electron microscopy and energy dispersive x ray. Saturated aqueous solutions were used to achieve controlled humidity environments. When the sensor was exposed to humidity environments, the electromotive force (EMF) of the sensor was examined. It was found that the sensor varies with the relative humidity (RH). The stable response curve was presented and non-Nernst behavior between the average EMF values and RH may be shown. PMID:21895252

Sun, Guoliang; Wang, Hairong; Jiang, Zhuangde

2011-08-01

368

A new sensitive organic/inorganic hybrid material based on titanium oxide for the potentiometric detection of iron(III).  

PubMed

The formation of a new hybrid material based on titanium dioxide as inorganic support and containing an iron organochelator (ICL670) is described. An organophosphorous coupling agent was used to graft the organic molecule on the oxide surface. The attachment of the organic substrate was well-confirmed by FTIR (DRIFT), solid-state (31)P and (13)C CPMAS NMR, thermal analysis and the integrity of the structural and morphological parameters were verified using XRD and TEM analyses. The interaction between the material and dissolved iron(III) was also investigated through potentiometric measurements and demonstrated the interest of this new non-siliceous based hybrid material. The obtained linear evolution of the open circuit potential from 10(-2) to 10(-6) mol L(-1) can be used for the analytical detection of iron(III). PMID:23000208

Becuwe, M; Rouge, P; Gervais, C; Courty, M; Dassonville-Klimpt, A; Sonnet, P; Baudrin, E

2012-12-15

369

Data Fusion from Voltammetric and Potentiometric Sensors to Build a Hybrid Electronic Tongue Applied in Classification of Beers  

NASA Astrophysics Data System (ADS)

A hybrid electronic tongue based on data fusion of two different sensor families was built and used to recognize three types of beer. The employed sensor array was formed by three modified graphite-epoxy voltammetric sensors plus six potentiometric sensors with cross-sensitivity. The sensors array coupled with feature extraction and pattern recognition methods, namely Principal Component Analysis (PCA) and Discriminant Factor Analysis (DFA), were trained to classify the data clusters related to different beer types. PCA was used to visualize the different categories of taste profiles and DFA with leave-one-out cross validation approach permitted the qualitative classification. According to the DFA model, 96% of beer samples were correctly classified. The aim of this work is to prove performance of hybrid electronic tongue systems by exploiting the new approach of data fusion of different sensor families, in comparison of electronic tongue with only one sensor type.

Haddi, Zouhair; Amari, Aziz; Bouchikhi, Benachir; Gutiérrez, Juan Manuel; Cetó, Xavier; Mimendia, Aitor; del Valle, Manel

2011-09-01

370

Louisiana ground-water map no. 8; potentiometric surface, 1991, of the Carrizo-Wilcox Aquifer in northwestern Louisiana  

USGS Publications Warehouse

In northwestern Louisiana, the Carrizo-Wilcox aquifer is the primary source of ground water within six parishes (Bossier, Caddo, De Soto, Natchitoches, Red River, and Sabine) and the secondary source in parts of three other parishes (Bienville, Claiborne, and Webster). Withdrawals from the aquifer increased from 4.7 Mgal/d (million gallons per day) in 1965 to 13.3 Mgal/d in 1990. A map of the potentiometric surface indicates that the altitudes of water levels in the Carrizo-Wilcox aquifer ranged from less than 100 feet to 300 feet above sea level in November and December 1991. The direction of ground-water flow within the aquifer generally is to the southeast and east or west to the Red River Valley.

Seanor, Ronald C.; Smoot, Charles W.

1995-01-01

371

Cation distributions on rapidly solidified cobalt ferrite  

NASA Technical Reports Server (NTRS)

The cation distributions in two rapidly solidified cobalt ferrites have been determined using Moessbauer spectroscopy at 4.2 K in an 8-T magnetic field. The samples were obtained by gas atomization of a Co0-Fe2O3-P2O5 melt. The degree of cation disorder in both cases was greater than is obtainable by cooling unmelted cobalt ferrite. The more rapidly cooled sample exhibited a smaller departure from the equilibrium cation distribution than did the more slowly cooled sample. This result is explained on the basis of two competing effects of rapid solidification: high cooling rate of the solid, and large undercooling.

De Guire, Mark R.; Kalonji, Gretchen; O'Handley, Robert C.

1990-01-01

372

Metal-cation-based anion exchange membranes.  

PubMed

Here we present the first metal-cation-based anion exchange membranes (AEMs), which were synthesized by copolymerization and cross-linking of a norbornene monomer functionalized with a water-soluble bis(terpyridine)ruthenium(II) complex and dicyclopentadiene. Each ruthenium complex has two associated counteranions, unlike most ammonium- and phosphonium-based membranes with single cation-anion pairs. The resulting AEMs show anion conductivities and mechanical properties comparable to those of traditional quaternary-ammonium-based AEMs as well as good alkaline stability and methanol tolerance. These results suggest that metal-cation-based polymers hold promise as a new class of materials for anion-conducting applications. PMID:22385221

Zha, Yongping; Disabb-Miller, Melanie L; Johnson, Zachary D; Hickner, Michael A; Tew, Gregory N

2012-03-14

373

THE PENETRATION OF SOME CATIONS INTO MUSCLE  

PubMed Central

The influx of Na+, K+, Rb+, and Cs+ into frog sartorius muscle has been followed. The results show that a maximum rate is found for K+, while Na+ and Cs+ penetrate much more slowly. Similar measurements with Ca++, Ba++, and Ra++ show that Ba++ penetrates at a rate somewhat greater than that of either Ca++ or Ra++. All these divalent cations, however, penetrate at rates much slower than do the alkali cations. The results obtained are discussed with reference to a model that has been developed to explain the different penetration rates for the alkali cations. PMID:13631206

Mullins, L. J.

1959-01-01

374

Spectroscopic characterization of alkane radical cations—I. Electronic absorption spectra of 3-methylalkane radical cations  

NASA Astrophysics Data System (ADS)

Radical cations of various 3-methylalkanes (C 6-C 14) have been produced and stabilized by ?-irradiation of the corresponding neutral compounds in saturated chloroflourocarbon (1,1-diflourotetra-chloroethane and 1,1,2-trichlorotriflouroethane) and perflourocarbon (perflourohexane and perfluoro-methylcyclohexane) matrices at 77 K. The perfluorocarbon matrices appeared more suitable for studies of the lighter radical cations, whereas the chlorofluorocarbon matrices were more suited for studies of the heavier radical cations; intermediary cations could be studied in both types of matrices. After irradiation, electronic absorptions associated with both the matrix and the alkane additive were observed. Pure spectra of the 3-methylalkane radical cations were obtained by difference spectrometry, after selective elimination of these cations by illumination. The electronic absorption spectra of the 3-methylalkane radical cations consist in all cases of a single broad absorption band. The spectral position of this band shifts to longer wavelengths with increasing chain length; the maximum of the absorption band was found to be situated at 490 nm for 3-methylpentane radical cations and at 940 nm for 3-methyltridecane radical cations. The results are most interesting because they give direct information on the electronic absorption of 3-methylpentane radical cations. It was found that the molar extinction coefficients of these cations are not very much smaller than those of other 3-methylalkane radical cations and thus must be of the order of 10 3dm 3·mol -1·cm -1. From this it is deduced that the majority of positive ions trapped in irradiated pure 3-methylpentane glasses at 77 K are not parent cations.

van den Bosch, Ann; Stienlet, Dominique; Ceulemans, Jan

375

Estimated 2012 groundwater potentiometric surface and drawdown from predevelopment to 2012 in the Santa Fe Group aquifer system in the Albuquerque metropolitan area, central New Mexico  

USGS Publications Warehouse

Historically, the water-supply requirements of the Albuquerque metropolitan area of central New Mexico were met almost exclusively by groundwater withdrawal from the Santa Fe Group aquifer system. In response to water-level declines, the Albuquerque Bernalillo County Water Utility Authority (ABCWUA) began diverting water from the San Juan-Chama Drinking Water Project in December 2008 to reduce the use of groundwater to meet municipal demand. Modifications in the demand for water and the source of the supply of water for the Albuquerque metropolitan area have resulted in a variable response in the potentiometric surface of the production zone (the interval of the aquifer, from within about 200 feet below the water table to 900 feet or more, in which supply wells generally are screened) of the Santa Fe Group aquifer system. Analysis of the magnitude and spatial distribution of water-level change can help improve the understanding of how the groundwater system responds to withdrawals and variations in the management of the water supply and can support water-management agencies’ efforts to minimize future water-level declines and improve sustainability. The U.S. Geological Survey (USGS), in cooperation with the ABCWUA, has developed an estimate of the 2012 potentiometric surface of the production zone of the Santa Fe Group aquifer system in the Albuquerque metropolitan area. This potentiometric surface is the latest in a series of reports depicting the potentiometric surface of the area. This report presents the estimated potentiometric surface during winter (from December to March) of water year 2012 and the estimated changes in potentiometric surface between predevelopment (pre-1961) and water year 2012 for the production zone of the Santa Fe Group aquifer system in the Albuquerque metropolitan area. Hydrographs from selected piezometers are included to provide details of historical water-level changes. In general, water-level measurements used for this report were collected in small-diameter observation wells screened over short intervals near the middle of the production zone and were considered to best represent the potentiometric head in the production zone. The water-level measurements were collected by various local and Federal agencies. The water year 2012 potentiometric surface map was created in a geographic information system, and the change in water-level altitude from predevelopment to water year 2012 was calculated. The 2012 potentiometric surface indicates that the general direction of groundwater flow is from the Rio Grande towards clusters of supply wells in the east, north, and west. Water-level changes from predevelopment to 2012 were variable across the Albuquerque metropolitan area. Estimated drawdown from 2008 was spatially variable across the Albuquerque metropolitan area. Hydrographs from piezometers on the east side of the river indicate an increase in the annual highest water-level measurement from 2008 to 2012. Hydrographs from piezometers in the northwest part of the study area indicate either steady decline of the water-level altitude over the period of record or recently variable trends in which water-level altitudes increased for a number of years but have declined since water year 2012.

Powell, Rachel I.; McKean, Sarah E.

2014-01-01

376

Structural behaviour differences in low methoxy pectin solutions in the presence of divalent cations (Ca(2+) and Zn(2+)): a process driven by the binding mechanism of the cation with the galacturonate unit.  

PubMed

In this paper, we compare the interactions between low methoxy pectin (LMP) and either Ca(2+) or Zn(2+) in semi-dilute solutions. Intrinsic viscosity and turbidity measurements reveal that pectin-calcium solutions are more viscous, but yet less turbid, than pectin-zinc ones. To get a molecular understanding of the origin of this rather unexpected behavior, we further performed isothermal titration calorimetry, small angle neutron scattering experiments, as well as molecular dynamics simulations. Our results suggest that calcium cations induce the formation of a more homogeneous network of pectin than zinc cations do. The molecular dynamics simulations indicate that this difference could originate from the way the two cations bind to the galacturonate unit (Gal), the main component of LMP: zinc interacts with both carboxylate and hydroxyl groups of Gal, in a similar way to that described in the so-called egg-box model, whereas calcium only interacts with carboxylate groups. This different binding behavior seems to arise from the stronger interaction of water molecules with zinc than with calcium. Accordingly, galacturonate chains are more loosely associated with each other in the presence of Ca(2+) than with Zn(2+). This may improve their ability to form a gel, not only by dimerization, but also by the formation of point-like cross-links. Overall, our results show that zinc binds less easily to pectin than calcium does. PMID:25425418

Assifaoui, Ali; Lerbret, Adrien; Uyen, Huynh T D; Neiers, Fabrice; Chambin, Odile; Loupiac, Camille; Cousin, Fabrice

2015-01-21

377

Misuse of thermodynamics in the interpretation of isothermal titration calorimetry data for ligand binding to proteins.  

PubMed

Isothermal titration calorimetry (ITC) has given a mass of data on the binding of small molecules to proteins and other biopolymers, with particular interest in drug binding to proteins chosen as therapeutic indicators. Interpretation of the enthalpy data usually follows an unsound protocol that uses thermodynamic relations in circumstances where they do not apply. Errors of interpretation include incomplete definitions of ligand binding and equilibrium constants and neglect of the non-ideality of the solutions under study, leading to unreliable estimates of standard free energies and entropies of binding. The mass of reported thermodynamic functions for ligand binding to proteins estimated from ITC enthalpies alone is consequently of uncertain thermodynamic significance and utility. ITC and related experiments to test the protocol assumptions are indicated. A thermodynamic procedure avoiding equilibrium constants or other reaction models and not requiring protein activities is given. The discussion draws attention to the fundamental but neglected relation between the thermodynamic activity and bioactivity of drugs and to the generally unknown thermodynamic status of ligand solutions, which for drugs relates directly to effective therapeutic dosimetry. PMID:25484232

Pethica, Brian A

2015-03-01

378

Probing the binding of procyanidin B3 to human serum albumin by isothermal titration calorimetry  

NASA Astrophysics Data System (ADS)

Proanthocyanidins are a mixture of monomers, oligomers, and polymers of flavan-3-ols that are widely distributed in the plant kingdom. One of the most widely studied proanthocyanidins is procyanidin B3. In this study, the interaction between procyanidin B3 and human serum albumin (HSA) was investigated using isothermal titration calorimetry (ITC). Thermodynamic investigations reveal that the hydrogen bond and van der Waals force are the major binding forces in the binding of procyanidin B3 to HSA. The binding of procyanidin B3 to HSA is driven by favorable enthalpy and unfavorable entropy. The obtained binding constant for procyanidin B3 with HSA is in the intermediate range and the equilibrium fraction of unbound procyanidin B3 fu > 90% at the physiological concentration of HSA shows that procyanidin B3 can be stored and transported from the circulatory system to reach its target site. The stoichiometric binding number n approximately equals to 1, suggesting that one molecule of procyanidin B3 combines with one molecule of HSA and no more procyanidin B3 binding to HSA occurs at the concentration used in this study.

Li, Xiangrong; Yan, Yunhui

2015-02-01

379

Real-Time Monitoring of Membrane-Protein Reconstitution by Isothermal Titration Calorimetry  

PubMed Central

Phase diagrams offer a wealth of thermodynamic information on aqueous mixtures of bilayer-forming lipids and micelle-forming detergents, providing a straightforward means of monitoring and adjusting the supramolecular state of such systems. However, equilibrium phase diagrams are of very limited use for the reconstitution of membrane proteins because of the occurrence of irreversible, unproductive processes such as aggregation and precipitation that compete with productive reconstitution. Here, we exemplify this by dissecting the effects of the K+ channel KcsA on the process of bilayer self-assembly in a mixture of Escherichia coli polar lipid extract and the nonionic detergent octyl-?-d-glucopyranoside. Even at starting concentrations in the low micromolar range, KcsA has a tremendous impact on the supramolecular organization of the system, shifting the critical lipid/detergent ratios at the onset and completion of vesicle formation by more than 2-fold. Thus, equilibrium phase diagrams obtained for protein-free lipid/detergent mixtures would be misleading when used to guide the reconstitution process. To address this issue, we demonstrate that, even under such nonequilibrium conditions, high-sensitivity isothermal titration calorimetry can be exploited to monitor the progress of membrane-protein reconstitution in real time, in a noninvasive manner, and at high resolution to yield functional proteoliposomes with a narrow size distribution for further downstream applications. PMID:24354292

2013-01-01

380

Adsorption of sodium dodecyl sulfate on functionalized graphene measured by conductometric titration.  

PubMed

We report on the adsorption of sodium dodecyl sulfate (SDS) onto functionalized graphene sheets (FGSs) in an aqueous system, measured at broad SDS and FGS concentration ranges by conductometric surfactant titration. At dilute SDS concentrations (<12 ?M in bulk solution), there is evidence of a counterion exchange between hydronium ions (from the dissociation of acidic chemical functionalities on FGS) and sodium ions coadsorbing with dodecyl sulfate monomers onto FGSs. We find that, for FGS with a carbon-to-oxygen ratio of ~18, monolayer adsorption of SDS on FGS reaches full surface coverage by ~12 ?M SDS. Additionally, the critical surface aggregation concentration (csac) for surface micelle formation on FGS is measured to be ~1.5 mM SDS. The transition from monolayer adsorption to surface micelle formation appears to occur at a similar SDS concentration on FGSs as on graphite, suggesting there is little difference in the surfactant adsorption behavior on both materials. We estimate that the FGS surface area available for SDS adsorption is ~600 m(2)/g, which is significantly less than expected for FGSs in suspension and indicates the presence of regions on FGS on which SDS adsorption does not occur. PMID:23734569

Hsieh, Andrew G; Punckt, Christian; Korkut, Sibel; Aksay, Ilhan A

2013-07-01

381

Development of a rapid titration method for predicting optimal coagulant concentration for filled tofu.  

PubMed

A rapid titration method was developed for predicting the optimal coagulant concentration for making filled tofu. Cooked soymilk (350 mL, 20 degrees C) in a 400 mL beaker was stirred by a magnetic stirrer to form a swirl. The quick-acting coagulant solution (20.0 Brix) was added into the soymilk at 1.0 mL/min. The swirl depth decreased when the soymilk viscosity increased as a result of increasing the concentration of coagulant in the soymilk. At a suitable stirrer speed, the swirl finally disappeared but the soymilk still maintained rotation, and then the swirl reappeared after around 1 min. The critical point of coagulant concentration (CPCC) was calculated on the basis of the volume of coagulant consumed to get the swirl to disappear. The influences of several factors on the CPCC were investigated, including coagulant addition rate, soymilk temperature, soymilk concentration, soymilk volume, stir bar length, and container size. For validation, 33 soybean samples were used to determine their CPCCs and make filled tofus. The results indicated that CPCC was a characteristic parameter of soymilk and could be used as an effective indicator for predicting optimal coagulant concentration. PMID:12926861

Liu, Zhi-Sheng; Chang, K C

2003-08-27

382

Temperature modulation and quadrature detection for selective titration of two-state exchanging reactants.  

PubMed

Biological samples exhibit huge molecular diversity over large concentration ranges. Titrating a given compound in such mixtures is often difficult, and innovative strategies emphasizing selectivity are thus demanded. To overcome limitations inherent to thermodynamics, we here present a generic technique where discrimination relies on the dynamics of interaction between the target of interest and a probe introduced in excess. Considering an ensemble of two-state exchanging reactants submitted to temperature modulation, we first demonstrate that the amplitude of the out-of-phase concentration oscillations is maximum for every compound involved in a reaction whose equilibrium constant is equal to unity and whose relaxation time is equal to the inverse of the excitation angular frequency. Taking advantage of this feature, we next devise a highly specific detection protocol and validate it using a microfabricated resistive heater and an epifluorescence microscope, as well as labeled oligonucleotides to model species displaying various dynamic properties. As expected, quantification of a sought for strand is obtained even if interfering reagents are present in similar amounts. Moreover, our approach does not require any separation and is compatible with imaging. It could then benefit some of the numerous binding assays performed every day in life sciences. PMID:21355619

Zrelli, K; Barilero, T; Cavatore, E; Berthoumieux, H; Le Saux, T; Croquette, V; Lemarchand, A; Gosse, C; Jullien, L

2011-04-01

383

Sequestering ability of phytate toward biologically and environmentally relevant trivalent metal cations.  

PubMed

Quantitative parameters for the interactions between phytate (Phy) and Al(3+), Fe(3+), and Cr(3+) were determined potentiometrically in NaNO(3) aqueous solutions at I = 0.10 mol L(-1) and T = 298.15 K. Different complex species were found in a wide pH range. The various species are partially protonated, depending on the pH in which they are formed, and are indicated with the general formula MH(q)Phy (with 0 ? q ? 6). In all cases, the stability of the FeH(q)Phy species is several log K units higher than that of the analogous AlH(q)Phy and CrH(q)Phy species. For example, for the MH(2)Phy species, the stability trend is log K(2) = 15.81, 20.61, and 16.70 for Al(3+), Fe(3+), and Cr(3+), respectively. The sequestering ability of phytate toward the considered metal cations was evaluated by calculating the pL(0.5) values (i.e., the total ligand concentration necessary to bind 50% of the cation present in trace in solution) at different pH values. In general, phytate results in a quite good sequestering agent toward all three cations in the whole investigated pH range, but the order of pL(0.5) depends on it. For example, at pH 5.0 it is pL(0.5) = 5.33, 5.44, and 5.75 for Fe(3+), Cr(3+), and Al(3+), respectively (Fe(3+) < Cr(3+) < Al(3+)); at pH 7.4 it is pL(0.5) = 9.94, 9.23, and 8.71 (Al(3+) < Cr(3+) < Fe(3+)), whereas at pH 9.0 it is pL(0.5) = 10.42, 10.87, and 8.34 (Al(3+) < Fe(3+) < Cr(3+)). All of the pL(0.5) values, and therefore the sequestering ability, regularly increase with increasing pH, and the dependence of pL(0.5) on pH was modeled using some empirical equations. PMID:22845864

Bretti, Clemente; Cigala, Rosalia Maria; Lando, Gabriele; Milea, Demetrio; Sammartano, Silvio

2012-08-22

384

Cationic antimicrobial (?-polylysine)-anionic polysaccharide (pectin) interactions: influence of polymer charge on physical stability and antimicrobial efficacy.  

PubMed

The cationic biopolymer ?-polylysine (?-PL) is a potent food-grade antimicrobial that is highly effective against a range of food pathogens and spoilage organisms. In compositionally complex systems such as foods and beverages, cationic ?-PL molecules may associate with anionic substances, leading to increased turbidity, sediment formation, and reduced antimicrobial activity. This study therefore characterized the interactions between cationic ?-PL and anionic pectins with different degrees of esterification (DE) and then investigated the influence of these interactions on the antimicrobial efficacy of ?-PL. The nature of the interactions was characterized using isothermal titration calorimetry (ITC), microelectrophoresis (ME), and turbidity measurements. High (DE 61%), medium (DE 51%), and low (DE 42%) methoxyl pectins interacted with ?-PL molecules through electrostatic forces, forming either soluble or insoluble complexes with various electrical charges, depending on the relative mass ratio of pectin and ?-PL. The interaction of pectin with ?-PL increased as the negative charge density on the pectin molecules increased, that is, with decreasing DE. The antimicrobial efficacy of ?-PL against two acid-resistant spoilage yeasts (Zygosaccharomyces bailii and Saccharomyces cerevisiae) decreased progressively in the presence of increasing levels of all three pectins. Nevertheless, the low DE pectin decreased the antimicrobial efficacy of ?-PL much more dramatically, likely due to strong electrostatic binding of ?-PL onto low DE pectin molecules reducing its interaction with anionic microbe surfaces. This study provides knowledge that will facilitate the rational application of ?-PL as an antimicrobial in complex food systems. PMID:22268773

Chang, Yuhua; McLandsborough, Lynne; McClements, David Julian

2012-02-22

385

Interactions and hybrid complex formation of anionic algal polysaccharides with a cationic glycine betaine-derived surfactant.  

PubMed

The interaction between anionic algal polysaccharides ((?)-, (?)-, (?)-carrageenans, alginate and ulvan) and a cationic glycine betaine (GB) amide surfactant possessing a C18:1 alkyl chain has been studied using isothermal titration calorimetry (ITC), zeta-potential measurements, dynamic light scattering (DLS), transmission electron microscopy (TEM), atomic force microscopy (AFM), and surface tension measurements. It was observed that this cationic surfactant derived from renewable raw materials induced cooperative binding with the anionic polymers at critical aggregation concentration (CAC) and the CAC values are significantly lower than the corresponding critical micelle concentration (CMC) for the surfactant. The CMC of cationic GB surfactant was obtained at higher surfactant concentration in polysaccharide solution than in pure water. More interestingly, the presence of original polysaccharide/surfactant hybrid complexes formed above the CMC value was evidenced from (?)-carrageenan by microscopy (TEM and AFM). Preliminary investigations of the structure of these complexes revealed the existence of surfactant nanoparticles surrounded with polysaccharide matrix, probably resulting from electrostatic attraction. In addition, ITC measurements clearly showed that the interactions of the ?-carrageenan was stronger than for other polysaccharides ((?)-, (?)-carrageenans, alginate and ulvan). These results may have important impact on the use of the GB amide surfactant in formulations based on algal polysaccharides for several applications such as in food, cosmetics, and detergency fields. PMID:25659719

Covis, Rudy; Vives, Thomas; Gaillard, Cédric; Benoit, Maud; Benvegnu, Thierry

2015-05-01

386

Mercury(II) removal from aqueous solutions and wastewaters using a novel cation exchanger derived from coconut coir pith and its recovery.  

PubMed

A new adsorbent (PGCP-COOH) having carboxylate functional group at the chain end was synthesized by grafting poly(hydroxyethylmethacrylate) onto coconut coir pith, CP (a coir industry-based lignocellulosic residue), using potassium peroxydisulphate as an initiator and in the presence of N,N'-methylenebisacrylamide as a cross-linking agent. The adsorbent was characterized with the help of infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy, and potentiometric titrations. The ability of PGCP-COOH to remove Hg(II) from aqueous solutions was assessed using batch adsorption technique under kinetic and equilibrium conditions. Adsorbent exhibits very high adsorption potential for Hg(II) and more than 99.0% removal was achieved in the pH range 5.5-8.0. Adsorption process was found to follow first-order-reversible kinetics. An increase of ionic strength of the medium caused a decrease in metal removal, indicating the occurrence of outer-sphere surface complex mechanism. The equilibrium data were fitted well by the Freundlich isotherm model (R(2)=0.99; chi(2)=1.81). The removal efficiency was tested using chlor-alkali industry wastewater. Adsorption isotherm experiments were also conducted for comparison using a commercial carboxylate-functionalized ion exchanger, Ceralite IRC-50. Regeneration experiments were tried for four cycles and results indicate a capacity loss of <9.0%. PMID:18313209

Anirudhan, T S; Divya, L; Ramachandran, M

2008-09-15

387

Aggregate transitions in mixtures of anionic sulfonate gemini surfactant with cationic ammonium single-chain surfactant.  

PubMed

Aggregation behaviors in mixtures of an anionic gemini surfactant 1,3-bis(N-dodecyl-N-propanesulfonate sodium)-propane (C(12)C(3)C(12)(SO(3))(2)) and a cationic single-chain surfactant cetyltrimethylammonium bromide (CTAB) have been investigated in aqueous solutions at pH 9.5 by turbidity, rheology, isothermal titration microcalorimetry (ITC), cryogenic transmission electron microscopy, and dynamic light scattering. Reversible aggregate transitions from spherical micelles to wormlike micelles, vesicles, and back to wormlike micelles and spherical micelles are successfully realized through fine regulation over the mixing ratio of surfactants, i.e., the anionic/cationic charge ratio. The five aggregate regions display distinguished phase boundaries so that the aggregate regions can be well controlled. From thermodynamic aspect, the ITC curves clearly reflect all the aggregate transitions and the related interaction mechanism. The self-assembling ability of the C(12)C(3)C(12)(SO(3))(2)/CTAB mixtures are significantly improved compared with both individual surfactants. Micelle growth from spherical to long wormlike micelles takes place at a relative low total concentration, i.e., 2.0 mM. The wormlike micelle solution at 10 mM or higher shows high viscosity and shear thinning property. Moreover, the C(12)C(3)C(12)(SO(3))(2)/CTAB mixtures do not precipitate even at 1:1 charge ratio and relative high concentration. It suggests that applying gemini surfactant should be an effective approach to improve the solubility of anionic/cationic surfactant mixtures and in turn may promote applications of the surfactant mixtures. PMID:23205820

Tian, Maozhang; Zhu, Linyi; Yu, Defeng; Wang, Yingxiong; Sun, Shufeng; Wang, Yilin

2013-01-10

388

Chitosan (polysaccharide) Cationic polyelectrolyte (NH3  

E-print Network

Chitosan (polysaccharide) Cationic polyelectrolyte (NH3 +) pH dependant solubility (pH to hydrogen evolution Chitosan molecules deprotonate and immobilized at electrode surface Electrochemical reaction rate depends on current density Electrochemical deposition of chitosan Thin film formation

Rubloff, Gary W.

389

Keteniminium ion-initiated cascade cationic polycyclization.  

PubMed

A novel and efficient keteniminium-initiated cationic polycyclization is reported. This reaction, which only requires triflic acid or bistriflimide as promoters, affords a straightforward entry to polycyclic nitrogen heterocycles possessing up to three contiguous stereocenters and seven fused cycles. These complex, polycyclic molecules can be obtained in a single operation from readily available ynamides which were shown to be remarkable building blocks for multiple, consecutive cationic transformations. PMID:24931745

Theunissen, Cédric; Métayer, Benoît; Henry, Nicolas; Compain, Guillaume; Marrot, Jérome; Martin-Mingot, Agnès; Thibaudeau, Sébastien; Evano, Gwilherm

2014-09-10

390

Test procedure for cation exchange chromatography  

SciTech Connect

The purpose of this test plan is to demonstrate the synthesis of inorganic antimonate ion exchangers and compare their performance against the standard organic cation exchangers. Of particular interest is the degradation rate of both inorganic and organic cation exchangers. This degradation rate will be tracked by determining the ion exchange capacity and thermal stability as a function of time, radiation dose, and chemical reaction.

Cooper, T.D.

1994-08-24

391

Method for encapsulating and isolating hazardous cations, medium for encapsulating and isolating hazardous cations  

DOEpatents

A method for encapsulating hazardous cations is provided comprising supplying a pretreated substrate containing the cations; contacting the substrate with an organo-silane compound to form a coating on the substrate; and allowing the coating to cure. A medium for containing hazardous cations is also provided, comprising a substrate having ion-exchange capacity and a silane-containing coating on the substrate. 3 figs.

Wasserman, S.R.; Anderson, K.B.; Song, K.; Yuchs, S.E.; Marshall, C.L.

1998-04-28

392

Synthesis of cation-intercalated titanate nanobelts.  

PubMed

Monovalent, bivalent and trivalent cations of Li+, Sn2+, Al3+, Fe3+ with different values of electronegativity were designed as doped-ions to prepare cations-intercalated titanate nanobelts through ex-situ ion-exchange reaction. XRD results revealed that the d200 values of layered TNBs decreased as the following sequence: Li-intercalated TNBs > Al-intercalated TNBs > Fe-intercalated TNBs > Sn-intercalated TNBs. The electronegativity differences between respective doped-cations and oxygen can well explain the trend of the reduction of d200 values for the synthesized layered nanobelts with different cations. The width change of nanobelts depending on intercalated cations showed similar tendency as that of d200 excluding Sn-intercalated case. That is mostly due to the crystallization of SnO2 nanoparticles on the nanobelts. Sn2+ is easily crystallized to form SnO2 nanoparticles on the surface of TNBs and being considered as unfavorable metal dopant for the present intercalation purpose. The reduction of d200 values of the doped TNBs from that of the undoped TNBs confirms the intercalation of the doped cations into layered structure. Such simple electronegativity-difference depending mechanism may be convenient for the designing of metal ion intercalation into octahedral TiO6 layered-oxide materials. PMID:22400335

Miao, Lei; Tanemura, Sakae; Huang, Rong; Liu, Chengyan; Huang, Chun Ming; Xu, Gang

2011-10-01

393

An efficient nonviral gene-delivery vector based on hyperbranched cationic glycogen derivatives  

PubMed Central

Background The purpose of this study was to synthesize and evaluate hyperbranched cationic glycogen derivatives as an efficient nonviral gene-delivery vector. Methods A series of hyperbranched cationic glycogen derivatives conjugated with 3-(dimethylamino)-1-propylamine (DMAPA-Glyp) and 1-(2-aminoethyl) piperazine (AEPZ-Glyp) residues were synthesized and characterized by Fourier-transform infrared and hydrogen-1 nuclear magnetic resonance spectroscopy. Their buffer capacity was assessed by acid–base titration in aqueous NaCl solution. Plasmid deoxyribonucleic acid (pDNA) condensation ability and protection against DNase I degradation of the glycogen derivatives were assessed using agarose gel electrophoresis. The zeta potentials and particle sizes of the glycogen derivative/pDNA complexes were measured, and the images of the complexes were observed using atomic force microscopy. Blood compatibility and cytotoxicity were evaluated by hemolysis assay and MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay, respectively. pDNA transfection efficiency mediated by the cationic glycogen derivatives was evaluated by flow cytometry and fluorescence microscopy in the 293T (human embryonic kidney) and the CNE2 (human nasopharyngeal carcinoma) cell lines. In vivo delivery of pDNA in model animals (Sprague Dawley rats) was evaluated to identify the safety and transfection efficiency. Results The hyperbranched cationic glycogen derivatives conjugated with DMAPA and AEPZ residues were synthesized. They exhibited better blood compatibility and lower cytotoxicity when compared to branched polyethyleneimine (bPEI). They were able to bind and condense pDNA to form the complexes of 100–250 nm in size. The transfection efficiency of the DMAPA-Glyp/pDNA complexes was higher than those of the AEPZ-Glyp/pDNA complexes in both the 293T and CNE2 cells, and almost equal to those of bPEI. Furthermore, pDNA could be more safely delivered to the blood vessels in brain tissue of Sprague Dawley rats by the DMAPA-Glyp derivatives, and then expressed as green fluorescence protein, compared with the control group. Conclusion The hyperbranched cationic glycogen derivatives, especially the DMAPA-Glyp derivatives, showed high gene-transfection efficiency, good blood compatibility, and low cyto toxicity when transfected in vitro and in vivo, which are novel potential nonviral gene vectors. PMID:24520193

Liang, Xuan; Ren, Xianyue; Liu, Zhenzhen; Liu, Yingliang; Wang, Jue; Wang, Jingnan; Zhang, Li-Ming; Deng, David YB; Quan, Daping; Yang, Liqun

2014-01-01

394

Combination of isothermal titration calorimetry and time-resolved luminescence for high affinity antibody-ligand interaction thermodynamics and kinetics  

PubMed Central

For experiments using synthetic ligands as probes for biological experiments, it is useful to determine the specificity and affinity of the ligands for their receptors. As ligands with higher affinities are developed (KA >108 M?1; KD <10?8 M), a new challenge arises: to measure these values accurately. Isothermal titration calorimetry measures heat produced or consumed during ligand binding, and also provides the equilibrium binding constant. However, as normally practiced, its range is limited. Displacement titration, where a competing weaker ligand is used to lower the apparent affinity of the stronger ligand, can be used to determine the binding affinity as well as the complete thermodynamic data for ligand-antibody complexes with very high affinity. These equilibrium data have been combined with kinetic measurements to yield the rate constants as well. We describe this methodology, using as an example antibody 2D12.5, which captures yttrium S-2-(4-aminobenzyl)-1, 4, 7, 10-tetraazacyclododecanetetraacetate. PMID:21964396

Aweda, Tolulope A.; Meares, Claude F.

2011-01-01

395

Low-dose, titratable interferon alfa in decompensated liver disease caused by chronic infection with hepatitis B virus  

Microsoft Academic Search

Background & Aims: Interferon therapy has been associated with a number of severe side effects when administered to patients with decompensated cirrhosis caused by chronic hepatitis B. The safety and potential efficacy of a low-dose, titratable regimen of interferon alfa-2b in patients with decompensated liver disease caused by chronic hepatitis B virus infection were studied. Methods: Twenty-six patients were treated

Robert Perrillo; Carlo Tamburro; Fredric Regenstein; Luis Balart; Henry Bodenheimer; Marcelo Silva; Eugene Schiff; Carol Bodicky; Barbara Miller; Cheryl Denham; Carmel Brodeur; Kathy Roach; Janice Albrecht

1995-01-01

396

Prediction of coagulation properties, titratable acidity, and pH of bovine milk using mid-infrared spectroscopy  

Microsoft Academic Search

This study investigated the potential application of mid-infrared spectroscopy (MIR 4,000-900 cm ?1 ) for the determination of milk coagulation properties (MCP), titratable acidity (TA), and pH in Brown Swiss milk samples (n = 1,064). Because MCP directly influence the efficiency of the cheese-making process, there is strong industrial interest in developing a rapid method for their assessment. Currently, the

M. De Marchi; C. C. Fagan; C. P. O’Donnell; A. Cecchinato; R. Dal Zotto; M. Cassandro; M. Penasa; G. Bittante

2009-01-01

397

Heat or insulation: behavioral titration of mouse preference for warmth or access to a nest.  

PubMed

In laboratories, mice are housed at 20-24°C, which is below their lower critical temperature (?30°C). This increased thermal stress has the potential to alter scientific outcomes. Nesting material should allow for improved behavioral thermoregulation and thus alleviate this thermal stress. Nesting behavior should change with temperature and material, and the choice between nesting or thermotaxis (movement in response to temperature) should also depend on the balance of these factors, such that mice titrate nesting material against temperature. Naïve CD-1, BALB/c, and C57BL/6 mice (36 male and 36 female/strain in groups of 3) were housed in a set of 2 connected cages, each maintained at a different temperature using a water bath. One cage in each set was 20°C (Nesting cage; NC) while the other was one of 6 temperatures (Temperature cage; TC: 20, 23, 26, 29, 32, or 35°C). The NC contained one of 6 nesting provisions (0, 2, 4, 6, 8, or 10g), changed daily. Food intake and nest scores were measured in both cages. As the difference in temperature between paired cages increased, feed consumption in NC increased. Nesting provision altered differences in nest scores between the 2 paired temperatures. Nest scores in NC increased with increasing provision. In addition, temperature pairings altered the difference in nest scores with the smallest difference between locations at 26°C and 29°C. Mice transferred material from NC to TC but the likelihood of transfer decreased with increasing provision. Overall, mice of different strains and sexes prefer temperatures between 26-29°C and the shift from thermotaxis to nest building is seen between 6 and 10 g of material. Our results suggest that under normal laboratory temperatures, mice should be provided with no less than 6 grams of nesting material, but up to 10 grams may be needed to alleviate thermal distress under typical temperatures. PMID:22479340

Gaskill, Brianna N; Gordon, Christopher J; Pajor, Edmond A; Lucas, Jeffrey R; Davis, Jerry K; Garner, Joseph P

2012-01-01

398

Thermodynamics of Interaction between Some Cellulose Ethers and SDS by Titration Microcalorimetry.  

PubMed

The interaction between certain nonionic cellulose ethers (ethyl hydroxyethyl cellulose and hydroxypropyl methyl cellulose) and sodium dodecyl sulphate (SDS) has been investigated using isothermal titration microcalorimetry at temperatures between 25-50 degrees C. The observed heat flow curves have been interpreted in terms of a plausible mechanism of the interaction of the substituent groups with SDS monomers and clusters. The data have been related to changes occuring in the system at the macro- and microscopic levels with the addition of surfactants and with temperature. The process consists predominantly of polymer-surfactant interactions initially and surfactant-surfactant interactions at the later stages. A phenomenological model of the cooperative interaction (adsorption) process has been derived, and earlier published equilibrium binding data have been used to recover binding constants and Gibbs energy changes for this process. The adsorption enthalpies and entropies have been recovered along with the heat capacity change. The enthalpic cost of confining the nonpolar regions of the polymers in surfactant clusters is high, but the entropy gain from release of hydration shell water molecules as well as increased freedom of movement of these nonpolar regions in the clusters gives the process a strong entropic driving force. The process is entropy-driven initially and converts to being both enthalpy and entropy-driven at high SDS concentrations. An enthalpy-entropy compensation behavior is seen. Strongly negative heat capacity changes have been obtained resulting from the transfer of nonpolar groups from aqueous into nonpolar environments, as well as a reduction of conformational domains that the chains can populate. Changes in these two components cause the heat capacity change to become less negative at the higher binding levels. The system can be classified as exhibiting nonclassical hydrophobic binding at the later stages of binding. Copyright 1999 Academic Press. PMID:10191016

Singh; Nilsson

1999-05-01

399

A Bovine Model of Respiratory Chlamydia psittaci Infection: Challenge Dose Titration  

PubMed Central

This study aimed to establish and evaluate a bovine respiratory model of experimentally induced acute C. psittaci infection. Calves are natural hosts and pathogenesis may resemble the situation in humans. Intrabronchial inoculation of C. psittaci strain DC15 was performed in calves aged 2–3 months via bronchoscope at four different challenge doses from 106 to 109 inclusion-forming units (ifu) per animal. Control groups received either UV-inactivated C. psittaci or cell culture medium. While 106 ifu/calf resulted in a mild respiratory infection only, the doses of 107 and 108 induced fever, tachypnea, dry cough, and tachycardia that became apparent 2–3 days post inoculation (dpi) and lasted for about one week. In calves exposed to 109 ifu C. psittaci, the respiratory disease was accompanied by severe systemic illness (apathy, tremor, markedly reduced appetite). At the time point of most pronounced clinical signs (3 dpi) the extent of lung lesions was below 10% of pulmonary tissue in calves inoculated with 106 and 107 ifu, about 15% in calves inoculated with 108 and more than 30% in calves inoculated with 109 ifu C. psittaci. Beside clinical signs and pathologic lesions, the bacterial load of lung tissue and markers of pulmonary inflammation (i.e., cell counts, concentration of proteins and eicosanoids in broncho-alveolar lavage fluid) were positively associated with ifu of viable C. psittaci. While any effect of endotoxin has been ruled out, all effects could be attributed to infection by the replicating bacteria. In conclusion, the calf represents a suitable model of respiratory chlamydial infection. Dose titration revealed that both clinically latent and clinically manifest infection can be reproduced experimentally by either 106 or 108 ifu/calf of C. psittaci DC15 while doses above 108 ifu C. psittaci cannot be recommended for further studies for ethical reasons. This defined model of different clinical expressions of chlamydial infection allows studying host-pathogen interactions. PMID:22299031

Reinhold, Petra; Ostermann, Carola; Liebler-Tenorio, Elisabeth; Berndt, Angela; Vogel, Anette; Lambertz, Jacqueline; Rothe, Michael; Rüttger, Anke; Schubert, Evelyn; Sachse, Konrad

2012-01-01

400

Energetics of carbohydrate binding to Momordica charantia (bitter gourd) lectin: an isothermal titration calorimetric study.  

PubMed

Physico-chemical and carbohydrate binding studies have been carried out on the Momordica charantia (bitter gourd) seed lectin (MCL). The lectin activity is maximal in the pH range 7.4-11.0, but decreases steeply below pH 7.0. The lectin activity is mostly unaffected in the temperature range 4-50 degrees C, but a sharp decrease is seen between 50 and 60 degrees C, which could be correlated to changes in the structure of the protein as seen by circular dichroism and fluorescence spectroscopy. Isothermal titration calorimetric studies show that the tetrameric MCL binds two sugar molecules and the binding constants (Kb), determined at 288.15 K, for various saccharides were found to vary between 7.3 x 10(3) and 1.52 x 10(4)M(-1). The binding reactions for all the saccharides investigated were essentially enthalpy driven, with the binding enthalpies (DeltaHb) at 288.15 K being in the range of -50.99 and -43.39 kJ mol(-1), whereas the contribution to the binding reaction from the entropy of binding was negative, with values of binding entropy (DeltaSb) ranging between -99.2 and -72.0 J mol(-1)K(-1) at 288.15 K. Changes in heat capacity (DeltaCp) for the binding of disaccharides, lactose and lactulose, were significantly larger in magnitude than those obtained for the monosaccharides, methyl-beta-D-galactopyranoside, and methyl-alpha-D-galactopyranoside, and could be correlated reasonably well with the surface areas of these ligands. Enthalpy-entropy compensation was observed for all the sugars studied, suggesting that water structure plays an important role in the overall binding reaction. CD spectroscopy indicates that carbohydrate binding does not lead to significant changes in the secondary and tertiary structures of MCL, suggesting that the carbohydrate binding sites on this lectin are mostly preformed. PMID:15820223

Sultan, Nabil Ali Mohammed; Swamy, Musti J

2005-05-01

401

The radical cation of trimethylphosphine oxide  

NASA Astrophysics Data System (ADS)

The structure of the gaseous long-lived radical cation generated upon electron ionization of trimethylphosphine oxide, (CH3)3PO, has been investigated by using ion-molecule reactions in a Fourier transform ion cyclotron resonance mass spectrometer. A radical cation with the connectivity of trimethylphosphine oxide is expected to react by facile electron transfer with triethylamine, pyridine and dimethyl disulfide since all these reactions are highly exothermic. However, no electron transfer reactions were observed. Instead, the radical cation transfers a proton to triethylamine and to pyridine, i.e., acts as a Brønsted acid. Further, the radical cation abstracts CH3S from dimethyl disulfide and hence demonstrates behavior characteristic of a distonic ion with a carbon radical center. This reactivity is unprecedented for a radical cation such as (CH3)3P+-O with the odd spin located at an oxygen atom. These experimental results indicate that the initially generated radical cation (CH3)3P+-O undergoes unimolecular isomerization to (CH3)2P+(OH)CH2 within a millisecond time frame. Ab initio molecular orbital calculations carried out at the unrestricted second-order Møller-Plesset (UMP2/6-31G** + ZPVE) level of theory support this conclusion by predicting that (CH3)2P+(OH)CH2 lies 23 kcal mol-1 lower in energy than (CH3)3P+-O. The energy barrier for unimolecular [1,3]-hydrogen atom migration in (CH3)3P+-O is estimated to be 24 kcal mol-1. This study demonstrates that the PO moiety provides a very strong driving force for hydrogen shifts in phosphorus containing radical cations.

Li, Ruomei; Schweighofer, Andreas; Keck, Helmut; Kuchen, Wilhelm; Kenttamaa, Hilkka I.

1996-12-01

402

Potentiometric Surfaces and Changes in Groundwater Levels in Selected Bedrock Aquifers in the Twin Cities Metropolitan Area, March-August 2008 and 1988-2008  

USGS Publications Warehouse

This report depicts potentiometric surfaces and groundwater- level changes in three aquifers that underlie the seven-county Twin Cities Metropolitan Area. Approximately 350 groundwater levels were measured in wells from the three aquifers-the Prairie du Chien-Jordan, the Franconia-Ironton-Galesville, and the Mount Simon-Hinckley aquifers-in March and August of 2008. The report presents maps, associated data tables, and 22 geographic information system datasets. The maps presented in this report show the potentiometric surfaces in March and August of 2008 for all three aquifers, groundwater-level changes from March to August 2008 for each aquifer, and revised potentiometric-surface contours for the winter of 1988-89 for the Prairie du Chien-Jordan and the Mount Simon-Hinckley aquifers, and the estimated long-term (winter of 1988-89 to March 2008) groundwater-level changes for the Prairie du Chien-Jordan and Mount Simon-Hinckley aquifers. This report documents the methods used to construct the maps and provides a context for the period of the measurements. Although withdrawal demand is increasing in the Twin Cities Metropolitan area, particularly in the Prairie du Chien-Jordan aquifer, year-to-year changes in withdrawals can be substantial, and the relation between potentiometric surfaces in the major aquifers and year-to-year withdrawals is not well established. The estimated long-term (19-year) groundwater-level changes for the Prairie du Chien-Jordan and Mount Simon-Hinckley aquifers have not been large based on data and maps produced during this study, despite the large seasonal fluctuations shown by the March and August 2008 synoptic measurements.

Sanocki, Christopher A.; Langer, Susan K.; Menard, Jason C.

2008-01-01

403

Potentiometric study of vitamin D 3 complexes with manganese(II), iron(II), iron(III) and zinc(II) in water—ethanol medium  

Microsoft Academic Search

Vitamin D3 (LH) complexes with manganese(II), iron(II), iron(III) and zinc(II) were identified in water-ethanol medium (30\\/70). Their stability constants were determined at 298 K and at a constant ionic strength of 0.100 M using potentiometric methods. The computerisation of the experimental data showed the presence of ML (M = metal, L = deprotonated vitamin D3) and ML2 species in all

B. Szpoganicz; M. A. Khan; X. Do Thanh; G. Bouet

1999-01-01

404

Cation Exchange in Kaolinite-Iron Oxide Systems  

Microsoft Academic Search

Kaolinite, to which iron oxides had been added by heating with FoC13 solution, was studied with regard to its cation exchange capacity. It was observed that net cations held (cations less anions) varied directly with pH. Cations and anions are removed in equivalent amounts when the clays arc washed with water, l%cmoval of exchangeable cations proceeds as the last anions

Grant W. Thomas; ALLEN R. SWOBODA

1962-01-01

405

Maps showing altitude of the potentiometric surface and changes in water level of the Sparta sand and Memphis sand aquifers in Eastern Arkansas, spring 1983  

USGS Publications Warehouse

The Sparta Sand and the Memphis Sand aquifers are a major source of industrial and public water supply and a minor but locally significant source of water for agricultural purposes in eastern and south-central Arkansas. The potentiometric surface map for this aquifer, compiled from water-level measurements made during the spring of 1983, indicates a generally southward potentiometric gradient. The potentiometric surface also illustrates the existence of three major cones of depression; one centered in Columbia County, one in Union County, and one in Jefferson County. Within the cones of depression, the majority of water withdrawn is utilized for industrial and public supply. The water-level change map for the Sparta Sand and the Memphis aquifer for the period between the springs of 1982 and 1983 shows overall a rise in water levels across the study area, including the cones of depression in Jefferson and Union Counties; however, water levels within the cone depression in Columbia County generally declined. (USGS)

Edds, Joe; Fitzpatrick, Daniel J.

1984-01-01

406

Preparation and application of cationic cellulose fibers modified by in situ grafting of cationic PVA  

Microsoft Academic Search

Rendering the cellulose fiber cationic via in situ graft copolymerization has been regarded as one of the effective approaches to improve the filler retention and distribution. In this work, cationic cellulose fibers were prepared by in situ copolymerization of vinyl acetate (VAc) and diallyldimethyl ammonium chloride (DADMAC) onto softwood sulphite pulp fibers using ceric ammonium nitrate (CAN) as a free

Yizhou Sang; Huining Xiao

2009-01-01

407

Estimation of Cation Exchange Capacity of Montmorillonite by Cationic Surfactant Adsorption  

Microsoft Academic Search

Cation exchange capacity (CEC) is one of the fundamental properties of clays and provides a means for estimating the general chemical properties of clays. The ammonium acetate saturation and sodium saturation methods are commonly used for measuring CEC. However, both methods are experimentally quite difficult and time consuming. This study investigates the feasibility of using cationic surfactant adsorption to determine

Chiougim Pan; Yun-Hwei Shen

2003-01-01

408

Use of Complementary Cation And Anion Heavy Atom-Atom Salt Derivatives to Solve the Structure of Cytochrome P450 46a1  

SciTech Connect

Human cytochrome P450 46A1 (CYP46A1) is one of the key enzymes in cholesterol homeostasis in the brain. The crystallization and heavy-atom structure solution of an active truncated CYP46A1 in complex with the high-affinity substrate analogue cholesterol-3-sulfate (CH-3S) is reported. The 2.6 {angstrom} structure of CYP46A1-CH-3S was solved using both anion and cation heavy-atom salts. In addition to the native anomalous signal from the haem iron, an NaI anion halide salt derivative and a complementary CsCl alkali-metal cation salt derivative were used. The general implications of the use of halide and alkali-metal quick soaks are discussed. The importance of using isoionic strength buffers, the titration of heavy-atom salts into different ionic species and the role of concentration are considered. It was observed that cation/anion-binding sites will occasionally overlap, which could negatively impact upon mixed RbBr soaks used for multiple anomalous scatterer MAD (MMAD). The use of complementary cation and anion heavy-atom salt derivatives is a convenient and powerful tool for MIR(AS) structure solution.

White, M.A.; Mast, N.; Bjorkhem, I.; Johnson, E.F.; Stout, C.D.; Pikuleva, I.A.

2009-05-26

409

Cationic acrylamide emulsion polymer brine thickeners  

SciTech Connect

This patent describes a thickened, solids free, aqueous drilling and servicing brine having a density of at least 14.4 ppg. comprising (a) an aqueous solution of at least one water-soluble salt of a multivalent metal, and (b) a cationic water-in-oil emulsion polymer of acrylamide or methacrylamide and a cationic monomer selected from the group consisting of a dialkylaminoalkyl acrylamide or methacrylamide, a trialkylaminoalkyl acrylamide or methacrylamide, a trialkylaminoalkyl acrylate or methacrylate, and a dialkyldialkyl ammonium halide. The acrylamide or methacrylamide to cationic monomer molar ratio of the polymer is about 70:30 to 95:5, the polymer having an I.V. in 1.0N KCl of about 1.0 to 7.0 dl/g and being present in a compatible and viscosifying amount; the thickened brine characterized by being substantially non-dilatent.

Gleason, P.A.; Piccoline, M.A.

1986-12-02

410

Divalent cation signaling in immune cells.  

PubMed

Divalent cations of two alkaline earth metals Ca(2+) and Mg(2+) and the transition metal Zn(2+) play vital roles in the immune system, and several immune disorders are associated with disturbances of their function. Until recently only Ca(2+) was considered to serve as a second messenger. However, signaling roles for Mg(2+) and Zn(2+) have been recently described, leading to a reevaluation of their role as potential second messengers. We review here the roles of these cations as second messengers in light of recent advances in Ca(2+), Mg(2+), and Zn(2+) signaling in the immune system. Developing a better understanding of these signaling cations may lead to new therapeutic strategies for immune disorders. PMID:24932518

Chaigne-Delalande, Benjamin; Lenardo, Michael J

2014-07-01

411

Cationically polymerizable monomers derived from renewable sources  

SciTech Connect

The objective of this project is to make use of products obtained from renewable plant sources as monomers for the direct production of polymers which can be used for a wide range of plastic applications. In this report is described progress in the synthesis and polymerization of cationically polymerizable monomers and oligomers derived from botanical oils, terpenes, natural rubber, and lignin. Nine different botanical oils were obtained from various sources, characterized and then epoxidized. Their photopolymerization was carried out using cationic photoinitiators and the mechanical properties of the resulting polymers characterized. Preliminary biodegradation studies are being conducted on the photopolymerized films from several of these oils. Limonene was cationically polymerized to give dimers and the dimers epoxidized to yield highly reactive monomers suitable for coatings, inks and adhesives. The direct phase transfer epoxidation of squalene and natural rubber was carried out. The modified rubbers undergo facile photocrosslinking in the presence of onium salts to give crosslinked elastomers. 12 refs., 3 figs., 10 tabs.

Crivello, J.V.

1991-10-01

412

A protocol analysis of the influence of technology on students' actions, verbal commentary, and thought processes during the performance of acid-base titrations  

Microsoft Academic Search

We investigated students' initial and final understanding of acid-base concepts and their concurrent thought processes and actions during the process of acid-base titrations. Here we report students' actions and thought processes while titrating. Different levels of information were presented by three technologies: chemical indicators, pH meters, and microcomputer-based laboratories. We speculated that the level of information would influence students' actions

Mary B. Nakhleh; Joseph S. Krajcik

1993-01-01

413

Water-Table and Potentiometric-Surface Altitudes in the Upper Glacial, Magothy, and Lloyd Aquifers beneath Long Island, New York, March-April 2006  

USGS Publications Warehouse

The U.S. Geological Survey (USGS), in cooperation with State and local agencies, systematically collects ground-water data at varying measurement frequencies to monitor the hydrologic situation on Long Island, New York. Each year during March and April, the USGS conducts a synoptic survey of hydrologic conditions to define the spatial distribution of the water table and potentiometric surfaces within the three main water-bearing units underlying Long Island - the upper glacial, Magothy, and Lloyd aquifers. These data and the maps constructed from them are commonly used in studies of Long Island's hydrology, and by water managers and suppliers for aquifer management and planning purposes. Water-level measurements made in 502 wells across Long Island during March-April 2006, were used to prepare the maps in this report. Measurements were made by the wetted-tape method to the nearest hundredth of a foot. Water-table and potentiometric-surface altitudes in these aquifers were contoured using these measurements. The water-table contours were interpreted using water-level data collected from 341 wells screened in the upper glacial aquifer and (or) shallow Magothy aquifer; the Magothy aquifer's potentiometric-surface contours were interpreted from measurements at 102 wells screened in the middle to deep Magothy aquifer and (or) contiguous and hydraulically connected Jameco aquifer; and the Lloyd aquifer's potentiometric-surface contours were interpreted from measurements at 59 wells screened in the Lloyd aquifer or contiguous and hydraulically connected North Shore aquifer. Many of the supply wells are in continuous operation and, therefore, were turned off for a minimum of 24 hours before measurements were made so that the water levels in the wells could recover to the level of the potentiometric head in the surrounding aquifer. Full recovery time at some of these supply wells can exceed 24 hours; therefore, water levels measured at these wells are assumed to be less accurate than those measured at observation wells, which are not pumped. In this report, all water-level altitudes are referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29).

Monti, Jack; Busciolano, Ronald J.

2009-01-01

414

Synthetic cationic antimicrobial peptides bind with their hydrophobic parts to drug site II of human serum albumin  

PubMed Central

Background Many biologically active compounds bind to plasma transport proteins, and this binding can be either advantageous or disadvantageous from a drug design perspective. Human serum albumin (HSA) is one of the most important transport proteins in the cardiovascular system due to its great binding capacity and high physiological concentration. HSA has a preference for accommodating neutral lipophilic and acidic drug-like ligands, but is also surprisingly able to bind positively charged peptides. Understanding of how short cationic antimicrobial peptides interact with human serum albumin is of importance for developing such compounds into the clinics. Results The binding of a selection of short synthetic cationic antimicrobial peptides (CAPs) to human albumin with binding affinities in the ?M range is described. Competitive isothermal titration calorimetry (ITC) and NMR WaterLOGSY experiments mapped the binding site of the CAPs to the well-known drug site II within subdomain IIIA of HSA. Thermodynamic and structural analysis revealed that the binding is exclusively driven by interactions with the hydrophobic moieties of the peptides, and is independent of the cationic residues that are vital for antimicrobial activity. Both of the hydrophobic moieties comprising the peptides were detected to interact with drug site II by NMR saturation transfer difference (STD) group epitope mapping (GEM) and INPHARMA experiments. Molecular models of the complexes between the peptides and albumin were constructed using docking experiments, and support the binding hypothesis and confirm the overall binding affinities of the CAPs. Conclusions The biophysical and structural characterizations of albumin-peptide complexes reported here provide detailed insight into how albumin can bind short cationic peptides. The hydrophobic elements of the peptides studied here are responsible for the main interaction with HSA. We suggest that albumin binding should be taken into careful consideration in antimicrobial peptide studies, as the systemic distribution can be significantly affected by HSA interactions. PMID:24456893

2014-01-01

415

A bovine model of respiratory Chlamydia psittaci infection: challenge dose titration.  

PubMed

This study aimed to establish and evaluate a bovine respiratory model of experimentally induced acute C. psittaci infection. Calves are natural hosts and pathogenesis may resemble the situation in humans. Intrabronchial inoculation of C. psittaci strain DC15 was performed in calves aged 2-3 months via bronchoscope at four different challenge doses from 10(6) to 10(9) inclusion-forming units (ifu) per animal. Control groups received either UV-inactivated C. psittaci or cell culture medium. While 10(6) ifu/calf resulted in a mild respiratory infection only, the doses of 10(7) and 10(8) induced fever, tachypnea, dry cough, and tachycardia that became apparent 2-3 days post inoculation (dpi) and lasted for about one week. In calves exposed to 10(9) ifu C. psittaci, the respiratory disease was accompanied by severe systemic illness (apathy, tremor, markedly reduced appetite). At the time point of most pronounced clinical signs (3 dpi) the extent of lung lesions was below 10% of pulmonary tissue in calves inoculated with 10(6) and 10(7) ifu, about 15% in calves inoculated with 10(8) and more than 30% in calves inoculated with 10(9) ifu C. psittaci. Beside clinical signs and pathologic lesions, the bacterial load of lung tissue and markers of pulmonary inflammation (i.e., cell counts, concentration of proteins and eicosanoids in broncho-alveolar lavage fluid) were positively associated with ifu of viable C. psittaci. While any effect of endotoxin has been ruled out, all effects could be attributed to infection by the replicating bacteria. In conclusion, the calf represents a suitable model of respiratory chlamydial infection. Dose titration revealed that both clinically latent and clinically manifest infection can be reproduced experimentally by either 10(6) or 10(8) ifu/calf of C. psittaci DC15 while doses above 10(8) ifu C. psittaci cannot be recommended for further studies for ethical reasons. This defined model of different clinical expressions of chlamydial infection allows studying host-pathogen interactions. PMID:22299031

Reinhold, Petra; Ostermann, Carola; Liebler-Tenorio, Elisabeth; Berndt, Angela; Vogel, Anette; Lambertz, Jacqueline; Rothe, Michael; Rüttger, Anke; Schubert, Evelyn; Sachse, Konrad

2012-01-01

416

Can a Tool That Automates Insulin Titration Be a Key to Diabetes Management?  

PubMed Central

Abstract Background Most patients who use insulin do not achieve optimal glycemic control and become susceptible to complications. Numerous clinical trials have shown that frequent insulin dosage titration is imperative to achieve glycemic control. Unfortunately, implementation of such a paradigm is often impractical. We hypothesized that the Diabetes Insulin Guidance System (DIGS™) (Hygieia, Inc., Ann Arbor, MI) software, which automatically advises patients on adjustment of insulin dosage, would provide safe and effective weekly insulin dosage adjustments. Subjects and Methods In a feasibility study we enrolled patients with type 1 and type 2 diabetes, treated with a variety of insulin regimens and having suboptimal glycemic control. The 12-week intervention period followed a 4-week baseline run-in period. During the intervention, DIGS processed patients' glucose readings and provided insulin dosage adjustments on a weekly basis. If approved by the study team, the adjusted insulin dosage was communicated to the patients. Insulin formulations were not changed during the study. The primary outcome was the fraction of DIGS dosage adjustments approved by the study team, and the secondary outcome was improved glycemic control. Results Forty-six patients were recruited, and eight withdrew. The DIGS software recommended 1,734 insulin dosage adjustments, of which 1,731 (99.83%) were approved. During the run-in period the weekly average glucose was stable at 174.2±36.7?mg/dL (9.7±2.0?mmol/L). During the following 12 weeks, DIGS dosage adjustments resulted in progressive improvement in average glucose to 163.3±35.1?mg/dL (9.1±1.9?mmol/L) (P<0.03). Mean glycosylated hemoglobin decreased from 8.4±0.8% to 7.9±0.9% (P<0.05). Concomitantly, the frequency of hypoglycemia decreased by 25.2%. Conclusions The DIGS software provided patients with safe and effective weekly insulin dosage adjustments. Widespread implementation of DIGS may improve the outcome and reduce the cost of implementing effective insulin therapy. PMID:22568777

Bergenstal, Richard M.; Bashan, Eran; McShane, Margaret; Johnson, Mary

2012-01-01

417

A fast response oxygen sensor based upon a fully-sealed zirconia pump-gauge operated in the potentiometric mode  

NASA Astrophysics Data System (ADS)

An instrument for fast and continuous measurement of oxygen partial pressure not requiring a reference gas was constructed around a sealed zirconia oxygen pump-gauge sensor operated in the ac mode. By appropriate signal processing of the gauge EMF, the mean oxygen partial pressure within the sensor was determined and maintained constant via a feedback loop. Potentiometric measurement of the oxygen partial pressure in the sample gas was made relative to this controlled internal reference. The response time of the instrument for a step change in oxygen partial pressure from 1 to 10 kPa was only 65 ms. ned" OutputMedium="All"> 1 3 Proceedings of the 29th International Conference on the Applications of the Mössbauer Effect (ICAME 2007) held in Kanpur, India, 14-19 October 2007, PART IV/VII 30 2008 11 19 2008 11 18 2008 7 2008 Springer Science+Business Media B.V. 2008 9803 10.1007/s10751-008-9803-9 1 On the phenomena occurring at the interface between iron and ironâ??platinum thin films 1 7 2008 9 17 2008 10 10 Springer Science+Business Media B.V.

Benammar, M.; Maskell, W. C.

1992-06-01

418

Determination of cadmium, lead and copper in milk and milk powder by means of flow potentiometric stripping analysis.  

PubMed

A flow potentiometric stripping analysis procedure for the determination of cadmium, lead and copper in milk and milk powder samples is described. The instrumental arrangement consists of a glassy-carbon thin-layer cell through which six different solutions may be drawn by means of a peristaltic pump and magnetically operated valves. The glassy-carbon electrode is pre-coated with a film of mercury which can be employed for several analytical runs. The sample, diluted five-fold with Suprapur hydrochloric acid, is electrolysed for 0.5-4 min prior to stripping in Suprapur hydrochloric acid. Pump-rate, electrolysis time and potential, opening and closing of inlet valves and digital evaluation of stripping times are controlled automatically by the computer. The analytical results agree satisfactorily with the certified values for three milk powder reference samples. The detection limit for cadmium, lead and copper in milk samples after 4, 1 and 0.5 min of pre-electrolysis is 0.8, 4 and 8 mug l. , respectively. An analytical procedure for the determination of lead in samples containing high concentrations of tin is described. PMID:18964242

Alamestrand, L; Jagner, D; Renman, L

1986-12-01

419

Automated determination of lead in urine by means of computerized flow potentiometric stripping analysis with a carbon-fibre electrode.  

PubMed

Five different digestion procedures have been investigated. In the recommended procedure 5 ml of concentrated hydrochloric acid-nitric acid mixture (1:1) were added to a 5-ml urine sample. After 1 min the sample was diluted to 100 ml with distilled water. The sample was divided into two 50-ml samples and to one of them a standard addition of 10 microg/l. lead(II) was made. The two samples were analysed fully automatically by means of computerized flow potentiometric stripping analysis, the main features of the procedure being mercury-film precoating, electrolysis of the sample for 90 sec and subsequent stripping in 1M calcium chloride/0.1M hydrochloric acid. Tin and copper were found not to interfere if present at concentrations below 50 mg/l. but high concentrations of tin had to be masked by the addition of copper in order to form a copper-tin intermetallic compound. Complexing agents used in lead poisoning therapy did not interfere with the determination. The lead concentration in a Seronorm reference urine sample was found to be 93 microg/l. with a standard deviation of 8 microg/l. (n = 5), the certified value being 88 microg/l. PMID:18964354

Huiliang, H; Jagner, D; Renman, L

1987-06-01

420

Potentiometric surface of the Upper Floridan aquifer in the Ichetucknee springshed and vicinity, northern Florida, September 2003  

USGS Publications Warehouse

The Upper Floridan aquifer is a highly permeable unit of carbonate rock extending beneath most of Florida and parts of southern Alabama, Georgia, and South Carolina. The high permeability is due in a large part to the widening of fractures that developed over time and the formation of conduits within the aquifer through dissolution of the limestone. This process has also produced numerous karst features such as springs, sinking streams, and sinkholes in northern Florida. These dissolution features, whether expressed at the surface or not, greatly influence the direction of ground-water flow in the Ichetucknee springshed adjacent to the Ichetucknee River. Ground water generally flows southwestward in the springshed and discharges to the Ichetucknee or Santa Fe Rivers, or to the springs along those rivers. This map depicts the September 9-10, 2003, potentiometric surface of the Upper Floridan aquifer based on 94 water-level measurements made by the Suwannee River Water Management District. Ground-water levels in this watershed fluctuate in response to precipitation and due to the high degree of interconnection between the surface-water system and the aquifer.

Sepulveda, A. Alejandro; Katz, Brian G.; Mahon, Gary L.

2006-01-01

421

Fabrication, characterization, and application of potentiometric immunosensor based on biocompatible and controllable three-dimensional porous chitosan membranes.  

PubMed

A novel three-dimensional porous chitosan membrane material was prepared as a matrix to encapsulate hepatitis B surface antibody (HBsAb) for fabrication of immunosensors. The porous chitosan matrix was prepared by electrodepositing a designer nanocomposite solution of chitosan-encapsulated silica nanoparticle hybrid film on an ITO electrode, and then removing the silica nanoparticles with HF solution. Using HBsAb as a model, the potentiometric immunosensor was constructed by linking HBsAb molecules to the three-dimensional porous chitosan film using glutaraldehyde as a cross-linker. Scanning electron microscopy was used to investigate the surface morphology of the three-dimensional porous chitosan films. Cyclic voltammograms and electrochemical impedance spectroscopy were used to probe the interfacial properties of the immunosensor. Results showed that the fabricated immunosensor with three-dimensional porous structure possessed high surface area, good mechanical stability, and good hydrophilicity, which provided a biocompatible microenvironment for maintaining the bioactivity of the immobilized protein and increased the protein loading. Therefore, the present immunosensor exhibits a wide linear range from 6.85 to 708 ng mL(-1) with a low detection limit of 3.89 ng mL(-1) for the detection of hepatitis B surface antigen (HBsAg). This work implied that the biocompatible and controllable three-dimensional porous chitosan membrane possessed potential applications for biosensing. PMID:18241878

Liang, Ruping; Peng, Hongzhen; Qiu, Jianding

2008-04-01

422

Use of Sequential Injection Analysis to construct a Potentiometric Electronic Tongue: Application to the Multidetermination of Heavy Metals  

NASA Astrophysics Data System (ADS)

An automated potentiometric electronic tongue (ET) was developed for the quantitative determination of heavy metal mixtures. The Sequential Injection Analysis (SIA) technique was used in order to automate the obtaining of input data, and the combined response was modeled by means of Artificial Neural Networks (ANN). The sensor array was formed by four sensors: two based on chalcogenide glasses Cd sensor and Cu sensor, and the rest on poly(vinyl chloride) membranes Pb sensor and Zn sensor. The Ion Selective Electrode (ISE) sensors were first characterized with respect to one and two analytes, by means of high-dimensionality calibrations, thanks to the use of the automated flow system; this characterization enabled an interference study of great practical utility. To take profit of the dynamic nature of the sensor's response, the kinetic profile of each sensor was compacted by Fast Fourier Transform (FFT) and the extracted coefficients were used as inputs for the ANN in the multidetermination applications. In order to identify the ANN which provided the best model of the electrode responses, some of the network parameters were optimized. Finally analyses were performed employing synthetic samples and water samples of the river Ebro; obtained results were compared with reference methods.

Mimendia, Aitor; Legin, Andrey; Merkoçi, Arben; del Valle, Manel

2009-05-01

423

Detection of circulating tumor cells in prostate cancer based on carboxylated graphene oxide modified light addressable potentiometric sensor.  

PubMed

Circulating tumor cells (CTCs) are a group of rare cancer cells that have detached from a primary tumor and circulate in the bloodstream. Herein, light addressable potentiometric sensor (LAPS) was exploited in the label-free detection of CTCs in the prostate cancer. To this end, the mouse anti-human epithelial cell adhesion molecule (anti-EpCAM) monoclonal antibody was selected as the probe to capture CTCs according to our western blot experiments, and therefore the anti-EpCAM was immobilized on the surface of carboxylated graphene oxide (GO-COOH) modified LAPS. Spiking experiments confirmed that LAPS' voltage decreased with the increasing of CTCs' concentration both in phosphate buffer (PBS) and blood, and as few as 10 CTCs in 1ml of blood could be detected, illustrating the high sensitivity of the proposed strategy. The analysis of healthy blood samples revealed no change in electrical signal, confirming the specificity of the system. Ultraviolet-visible (UV-vis) spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and immunofluorescent assay (IFA) were conducted to characterize GO-COOH, testify its existence on LAPS and validate CTCs' capturing by anti-EpCAM grafted on GO-COOH modified substrates. It is indicated that LAPS could be a potential platform for CTCs detection and may provide a powerful tool for downstream analysis. PMID:25460877

Gu, Yajun; Ju, Cheng; Li, Yanjun; Shang, Zhiqun; Wu, Yudong; Jia, Yunfang; Niu, Yuanjie

2015-04-15

424

Organically nanoporous silica gel based on carbon paste electrode for potentiometric detection of trace Cr(III).  

PubMed

A new ion-selective electrode (ISE) for the detection of trace chromium(III) was designed by using 2-acetylpyridine and nanoporous silica gel (APNSG)-functionalized carbon paste electrode (CPE). The presence of APNSG acted as not only a paste binder, but also a reactive material. With 7.5 wt% APNSG proportions, the developed electrode exhibited wide dynamic range of 1.0 x 10(-8) to 1.0 x 10(-3) M toward Cr(III) with a detection limit of 8.0 x 10(-9) M and a Nernstian slope of 19.8 +/- 0.2 mV decade(-1). The as-prepared electrode displayed rapid response (approximately 55 s), long-time stability, and high sensitivity. Moreover, the potentiometric responses could be carried out with wide pH range of 1.5-5.0. In addition, the content of Cr(III) in food samples, e.g. coffee and tea leaves, has been assayed by the developed electrode, atomic absorption spectrophotometer (AAS) and atomic emission spectrometer (ICP-AES), respectively, and consistent results were obtained. Importantly, the response mechanism of the proposed electrode was investigated by using AC impedance and UV-vis spectroscopy. PMID:19591707

Zhou, Wei; Chai, Yaqin; Yuan, Ruo; Guo, Junxiang; Wu, Xia

2009-08-11

425

Characterization of Copper(II) Interactions with Sinefungin, a Nucleoside Antibiotic: Combined Potentiometric, Spectroscopic and DFT Studies  

PubMed Central

Interactions between sinefungin and copper(II) ions were investigated. Stoichiometry and stability constants of the metal-free system and two mononuclear complexes present in solution were determined on the basis of potentiometric data analysis. The results were compared to the Cu(II)-ornithine system due to structural similarities between both molecules. Combined spectroscopic and theoretical studies allowed for determination of coordination pattern for the Cu(II)-sinefungin complexes. At acidic pH, copper is bound in “glycine-like” coordination mode, identical with that of ornithine. This involves ?-amino group and the carboxyl oxygen. At higher pH, a “bis-complex” is formed by two sinefungin molecules. The second ligand binds in equatorial position displacing two water molecules, what results in the stable {2N,2O} coordination. Both axial positions are supposed to be occupied by N1 nitrogen donors of adenine moiety, what is confirmed by DFT calculations. They interact indirectly with copper(II) through water molecules as the result of dominant syn conformation of purine. PMID:18273386

Jaworska, Maria; Lodowski, Piotr; Mucha, Ariel; Szczepanik, Wojciech; Valensin, Gianni; Cappannelli, Massimo; Je?owska-Bojczuk, Ma?gorzata

2007-01-01

426

Cationic dialkylarylphosphates: a new family of bio-inspired cationic lipids for gene delivery.  

PubMed

In this work that aims to synthesize and evaluate new cationic lipids as vectors for gene delivery, we report the synthesis of a series of cationic lipids in which a phosphate functional group acts as a linker to assemble on a molecular scale, two lipid chains and one cationic polar head. The mono or dicationic moiety is connected to the phosphate group by an aryl spacer. In this work, two synthesis strategies were evaluated. The first used the Atherton-Todd coupling reaction to introduce a phenolic derivative to dioleylphosphite. The second strategy used a sequential addition of lipid alcohol and a phenolic derivative on POCl3. The two methods are efficient, but the latter allows larger yields. Different polar head groups were introduced, thus producing amphiphilic compounds possessing either one permanent (N-methyl-imidazolium, pyridinium, trimethylammonium) or two permanent cationic charges. All these cationic lipids were formulated as liposomal solutions and characterized (size and zeta potential). They formed stable liposomal solutions both in water (at pH 7.0) and in a weakly acidic medium (at pH 5.5). Finally, this new generation of cationic lipids was used to deliver DNA into various human-derived epithelial cells cultured in vitro. Compared with Lipofectamine used as a reference commercial lipofection reagent, some cationic dialkylarylphosphates were able to demonstrate potent gene transfer abilities, and noteworthily, monocationic derivatives were much more efficient than dicationic analogues. PMID:25420449

Le Corre, Stéphanie S; Belmadi, Nawal; Berchel, Mathieu; Le Gall, Tony; Haelters, Jean-Pierre; Lehn, Pierre; Montier, Tristan; Jaffrès, Paul-Alain

2015-01-28

427

Interactions of poly(amidoamine) dendrimers with the surfactants SDS, DTAB, and C12EO6: an equilibrium and structural study using a SDS selective electrode, isothermal titration calorimetry, and small angle neutron scattering.  

PubMed

Interactions in aqueous solutions of different generations of poly(amidoamine) (PAMAM) dendrimers containing amine, hydroxyl, or delta-glucolactone functional groups at the periphery with the anionic surfactant sodium dodecyl sulfate (SDS) were investigated. We used a SDS-specific electrode (EMF) for SDS monomer concentration monitoring, isothermal titration calorimetry (ITC) for binding information, and small angle neutron scattering (SANS) for structural studies. ITC experiments monitoring the interaction of the dendrimers with cationic dodecyltrimethylammonium bromide (DTAB) and nonionic hexaethylene glycol mono-n-dodecyl ether (C12EO6) showed no significant binding effects. In contrast, SDS binds to all of the above dendrimers. EMF and ITC data demonstrated a regular trend for both the onset of binding and binding saturation as the generation in each family of dendrimers increased. In addition, generation G6 exhibited a noncooperative binding process at very low SDS concentrations. Furthermore, the onset of cooperative binding in the EMF experiments started at lower concentrations as the weight % (w/v), the size, and the numbers of the internal or surface groups increased. On the other hand, the binding capacity of the dendrimers showed only a small dependence on the above parameters. At SDS concentrations approaching the binding limit and also at selective concentrations within the binding range, SANS measurements indicated that in all cases the bound surfactant is in the micellar form. From the electromotive force (EMF) measurements, ITC data, and SANS data, the stoichiometry of the supramolecular complexes was determined. PMID:15461524

Sidhu, J; Bloor, The Late D M; Couderc-Azouani, S; Penfold, J; Holzwarth, J F; Wyn-Jones, E

2004-10-12

428

Process and apparatus for the production of Bi-213 cations  

DOEpatents

A process for producing substantially impurity-free Bi-213 cations is disclosed. An aqueous acid feed solution containing Ac-225 cations is contacted with an ion exchange medium to bind the Ac-225 cations and form an Ac-225-laden ion exchange medium. The bound Ac-225 incubates on the ion exchange medium to form Bi-213 cations by radioactive decay. The Bi-213 cations are then recovered from the Ac-225-laden ion exchange medium to form a substantially impurity-free aqueous Bi-213 cation acid solution. An apparatus for carrying out this process is also disclosed. 7 figs.

Horwitz, E.P.; Hines, J.J.; Chiarizia, R.; Dietz, M.

1998-12-29

429

Process and apparatus for the production of BI-213 cations  

DOEpatents

A process for producing substantially impurity-free Bi-213 cations is disclosed. An aqueous acid feed solution containing Ac-225 cations is contacted with an ion exchange medium to bind the Ac-225 cations and form an Ac-225-laden ion exchange medium. The bound Ac-225 incubates on the ion exchange medium to form Bi-213 cations by radioactive decay. The Bi-213 cations are then recovered from the Ac-225-laden ion exchange medium to form a substantially impurity-free aqueous Bi-213 cation acid solution. An apparatus for carrying out this process is also disclosed.

Horwitz, E. Philip (Naperville, IL); Hines, John J. (Newark, IL); Chiarizia, Renato (Elmhurst, IL); Dietz, Mark (Elmhurst, IL)

1998-01-01

430

Restructuring of a Peat in Interaction with Multivalent Cations: Effect of Cation Type and Aging Time  

PubMed Central

It is assumed to be common knowledge that multivalent cations cross-link soil organic matter (SOM) molecules via cation bridges (CaB). The concept has not been explicitly demonstrated in solid SOM by targeted experiments, yet. Therefore, the requirements for and characteristics of CaB remain unidentified. In this study, a combined experimental and molecular modeling approach was adopted to investigate the interaction of cations on a peat OM from physicochemical perspective. Before treatment with salt solutions of Al3+, Ca2+ or Na+, respectively, the original exchangeable cations were removed using cation exchange resin. Cation treatment was conducted at two different values of pH prior to adjusting pH to 4.1. Cation sorption is slower (>>2 h) than deprotonation of functional groups (<2 h) and was described by a Langmuir model. The maximum uptake increased with pH of cation addition and decreased with increasing cation valency. Sorption coefficients were similar for all cations and at both pH. This contradicts the general expectations for electrostatic interactions, suggesting that not only the interaction chemistry but also spatial distribution of functional groups in OM determines binding of cations in this peat. The reaction of contact angle, matrix rigidity due to water molecule bridges (WaMB) and molecular mobility of water (NMR analysis) suggested that cross-linking via CaB has low relevance in this peat. This unexpected finding is probably due to the low cation exchange capacity, resulting in low abundance of charged functionalities. Molecular modeling demonstrates that large average distances between functionalities (?3 nm in this peat) cannot be bridged by CaB-WaMB associations. However, aging strongly increased matrix rigidity, suggesting successive increase of WaMB size to connect functionalities and thus increasing degree of cross-linking by CaB-WaMB associations. Results thus demonstrated that the physicochemical structure of OM is decisive for CaB and aging-induced structural reorganisation can enhance cross-link formation. PMID:23750256

Kunhi Mouvenchery, Yamuna; Jaeger, Alexander; Aquino, Adelia J. A.; Tunega, Daniel; Diehl, Dörte; Bertmer, Marko; Schaumann, Gabriele Ellen

2013-01-01

431

Method for encapsulating and isolating hazardous cations, medium for encapsulating and isolating hazardous cations  

SciTech Connect

The problems associated with the disposal of toxic metals in an environmentally acceptable manner continues to plague industry. Such metals as nickel, vanadium, molybdenum, cobalt, iron, and antimony present physiological and ecological challenges that are best addressed through minimization of exposure and dispersion. A method for encapsulating hazardous cations is provided comprising supplying a pretreated substrate containing the cations; contacting the substrate with an organo-silane compound to form a coating on the substrate; and allowing the coating to cure. A medium for containing hazardous cations is also provided, comprising a substrate having ion-exchange capacity and a silane-containing coating on the substrate.

Wasserman, S.R.; Anderson, K.B.; Song, K.; Yuchs, S.E.; Marshall, C.L.

1996-12-31

432

Thermodynamics of ion binding to phosphatidic acid bilayers. Titration calorimetry of the heat of dissociation of DMPA.  

PubMed

The heat of dissociation of the second proton of 1,2-dimyristoylphosphatidic acid (DMPA) was studied as a function of temperature using titration calorimetry. The dissociation of the second proton of DMPA was induced by addition of NaOH. From the calorimetric titration experiment, the intrinsic pK0 for the dissociation reaction could be determined by applying the Gouy-Chapman theory. pK0 decreases with temperature from ca. 6.2 at 11 degrees C to 5.4 at 54 degrees C. From the total heat of reaction, the dissociation enthalpy, delta Hdiss, was determined by subtracting the heat of neutralization of water and the heat of dilution of NaOH. In the temperature range between 2 and 23 degrees C, delta Hdiss is endothermic with an average value of ca. 2.5 kcal.mol-1 and shows no clear-cut temperature dependence. In the temperature range between 23 and 52 degrees C, delta Hdiss calculated after subtraction of the heat of neutralization and dilution is not the true dissociation enthalpy but includes contributions from the phase transition enthalpy, delta Htrans, as the pH jump induces a transition from the gel to the liquid-crystalline phase. The delta Cp for the reaction enthalpy observed in this temperature range is positive. Above 53 degrees C, the pH jump induces again only the dissociation of the second proton, and the bilayers stay in the liquid-crystalline phase. In this temperature range, delta Hdiss seems to decrease with temperature. The thermodynamic data from titration calorimetry and differential scanning calorimetry as a function of pH can be combined to construct a complete enthalpy-temperature diagram of DMPA in its two ionization states. PMID:1316155

Blume, A; Tuchtenhagen, J

1992-05-19

433

ADSORPTION OF ORGANIC CATIONS TO NATURAL MATERIALS  

EPA Science Inventory

The factors that control the extent of adsorption of amphiphilic organic cations on environmental and pristine surfaces have been studied. The sorbents were kaolinite, montmorillonite, two aquifer materials, and a soil; solutions contained various concentrations of NaCl and CaCl,...

434

ADSORPTION OF ORGANIC CATIONS TO NATURAL MATERIALS  

EPA Science Inventory

The factors that control the extent of adsorption of amphiphilic organic cations on environmental and pristine surfaces have been studied. he sorbents were kaolinite, montmorillonite, two aquifer materials, and a soil; solutions contained various concentrations of NaCl and CaC12,...

435

Cationic peptides: a new source of antibiotics  

Microsoft Academic Search

Antimicrobial cationic peptides are an important component of the innate defenses of all species of life. Different peptides may have antibacterial, antiendotoxic, antibiotic-potentiating or antifungal properties, and so they are being developed for use as a novel class of antimicrobial agents and as the basis for making transgenic disease-resistant plants and animals.

Robert E. W Hancock; Robert Lehrer

1998-01-01

436

Lazy Narrowing with Simpli cation Michael Hanus  

E-print Network

Lazy Narrowing with Simpli#12;cation #3; Michael Hanus Informatik II, RWTH Aachen D-52056 Aachen of two natural numbers which are represented by terms built from 0 and s: 0 + y ! y (R 1 ) s(x) + y ! s(x + y) (R 2 ) #3; This paper is a revised version of papers appeared in the proceedings of ESOP'94

Hanus, Michael

437

Viscoelastic cationic polymers containing the urethane linkage  

NASA Technical Reports Server (NTRS)

A method for the synthesis and manufacturing of elastomeric compositions and articles containing quaternary nitrogen centers and condensation residues along the polymeric backbone of the centers is presented. Linear and cross-linked straight chain and block polymers having a wide damping temperature range were synthesized. Formulae for the viscoelastic cationic polymers are presented.

Rembaum, A. (inventor)

1972-01-01

438

Bioaccumulation of metal cations by Saccharomyces cerevisiae  

Microsoft Academic Search

Yeast cells are capable of accumulation of various heavy metals, preferentially accumulating those of potential toxicity and also those of value. They retain their ability to accumulate heavy metals under a wide range of ambient conditions. In the present study it was shown that yeast cells in suspension accumulate heavy metal cations such as Cu2+, Co2+. The level of copper