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1

Potentiometric Titration Method for Quantitative Determination of Hydrogen Peroxide.  

National Technical Information Service (NTIS)

An electrochemical potentiometric titration method that entails titration of a known volume of a catholyte containing an unknown amount of hydrogen peroxide in a titration cell having two electrodes, a platinum working electrode and a silver/silver chlori...

R. R. Bessette

2005-01-01

2

Potentiometric Acid-Base Titrations with Activated Graphite Electrodes  

NASA Astrophysics Data System (ADS)

Dry cell graphite (DCG) electrodes activated with potassium permanganate are employed as potentiometric indicator electrodes for acid-base titrations. Special attention is given to an indicator probe comprising activated DCG-non-activiated DCG electrode couple. This combination also proves suitable for the titration of strong or weak acids.

Riyazuddin, P.; Devika, D.

1997-10-01

3

Surface properties and modeling potentiometric titration of aqueous illite suspensions  

Microsoft Academic Search

The potentiometric titration behavior of complex illitic clay minerals provided from different origins (two Tunisian illite\\u000a samples and an American illite sample) was investigated and interpreted according to the surface complexation theory. In the\\u000a present investigation, the focus is on the surface charge characteristics. The proton surface charge can be calculated by\\u000a subtracting the supernatant titration curves from those of

A. Kriaa; N. Hamdi; E. Srasra

2008-01-01

4

Potentiometric/turbidometric titration of antiperspirant actives.  

PubMed

A titration procedure that simultaneously monitors the pH and turbidity of an antiperspirant solution during neutralization with sodium hydroxide was developed to characterize antiperspirant actives. Aluminum chloride, aluminum chlorohydrate (ACH), and aluminum zirconium glycine complex (AZG) gave distinctive pH/turbidity profiles. The activated forms of aluminum chlorohydrate (ACH') and aluminum zirconium glycine complex (AZG') produced more turbidity than the non-activated forms. On an equimolar basis, AZG' produced more turbidity than any of the antiperspirant actives tested. PMID:12715089

Johnston, Clifford T; Hem, Stanley L; Guenin, Eric; Mattai, Jairajh; Afflito, John

5

Assay of quaternary ammonium antimicrobial compounds by aqueous potentiometric titration  

Microsoft Academic Search

An automatic potentiometric titration method for the determination of quaternary ammonium antimicrobial compounds at the macro\\u000a level is described. The procedure involves the use of standard sodium lauryl sulfate as the titrant and a nitrate ion-selective\\u000a or surfactant electrode to detect the end point. The method, which includes a new, simpler means of titrant standardization,\\u000a avoids the use of hazardous

George T. Battaglini

2002-01-01

6

Potentiometric titration of gold, platinum, and some other precious metals  

SciTech Connect

Gold, platinum, and several other platinum metals can be determined by titration with cetylpyridinium chloride (CPC). CPC forms a precipitate with AuCl{sub 4}{sup {minus}} and PtCl{sub 6}{sup 2{minus}}. Differentiation of AuCl{sub 4{minus}} and PtCl{sub 6}{sup 2{minus}} with this titrant is not possible; however, their sum can be determined. Titration with tetraphenylarsonium chloride at pH 1 is selective for tetrachloroaurate, which thus can be determined in the presence of hexachloroplatinate. Hexachloroosmate(IV), tetrachloroplatinite(II), tetrachloropalladate(II), hexachloropalladate(IV), and hexachloroiridate(IV) can also be determined potentiometrically vs. CPC. The indicating electrode is prepared by coating a spectroscopic graphite rod with a solution of poly(vinyl chloride) (PVC) and dioctylphthalate (DOP) in tetrahydrofuran (THF). Gold in gold cyanide plating baths and in potassium aurocyanide can be determined by potentiometric titration vs standard silver nitrate, using a silver ion-selective indicating electrode. The monovalent gold need not be converted to the trivalent state with aqua regia, resulting in a considerable saving of time and effort. Free cyanide and aurocyanide can be titrated sequentially by this method. Chloride does not interfere and can, in fact, also be sequentially determined. 17 refs., 2 figs., 3 tabs.

Selig, W.S.

1991-02-04

7

Semi-automated potentiometric titration method for uranium characterization.  

PubMed

The manual version of the potentiometric titration method has been used for certification and characterization of uranium compounds. In order to reduce the analysis time and the influence of the analyst, a semi-automatic version of the method was developed in the Brazilian Nuclear Energy Commission. The method was applied with traceability assured by using a potassium dichromate primary standard. The combined standard uncertainty in determining the total concentration of uranium was around 0.01%, which is suitable for uranium characterization. PMID:22154105

Cristiano, B F G; Delgado, J U; da Silva, J W S; de Barros, P D; de Araújo, R M S; Lopes, R T

2011-11-25

8

Estimation of ? and ? peptide bonds in thermal poly(aspartic acid) by potentiometric titration  

Microsoft Academic Search

A potentiometric titration method for the estimation of the configuration (a and ß peptide bonds, I and II) of poly (aspartic acid) prepared by thermal polycondensation is presented. Experimental results of the potentiometric titration of various samples differing in the molar fraction of I and II are confronted with the results of 13C NMR spectroscopy. Both methods lead to comparable

V. Saudek; J. Drobnik

1981-01-01

9

Potentiometric Titration of Alkyl Aromatic Sulfonates Using a PVC Membrane Electrode.  

National Technical Information Service (NTIS)

A potentiometric titration method for determinig high-equivalent-weight sulfonates has been developed. This method utilizes a precipitation reaction between sulfonate and quaternary ammonium ions. A PVC (polyvinyl chloride) membrane electrode, which respo...

S. H. Hoke A. G. Collins

1979-01-01

10

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

11

Potentiometric titration of alkyl aromatic sulfonates using a PVC membrane electrode  

Microsoft Academic Search

A potentiometric titration method for determinig high-equivalent-weight sulfonates has been developed. This method utilizes a precipitation reaction between sulfonate and quaternary ammonium ions. A PVC (polyvinyl chloride) membrane electrode, which responds to the quaternary ammonium titrant, signals the end point of the titration. Interferences from inorganic and organic anions have been examined. Compared with the visual Methylene Blue Method, this

S. H. Hoke; A. G. Collins

1979-01-01

12

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

13

Determination of uranyl ion by potentiometric titration using an uranyl-selective electrode  

Microsoft Academic Search

A potentiometric titration of uranyl ion is described using an uranyl selective electrode based on a membrane containing a complex of UO2-bis[di-4-(1,1,3,3-tetra-methylbutyl)phenyl phosphate] as an ion-exchanger and tritolyl phosphate as a solvent mediator. The titrations were carried out with various titrants: sodium hydroxide, potassium fluoride and sodium salts of acetate, oxalate and citrate. The equivalence points were determined by Gran's

Nabil S. Nassory

1990-01-01

14

Pulsating potentiometric titration technique for assay of dissolved oxygen in water at trace level  

Microsoft Academic Search

A simple but high performance potentiometric titration technique using pulsating sensors has been developed for assay of dissolved oxygen (DO) in water samples down to 10.0?gL?1 levels. The technique involves Winkler titration chemistry, commonly used for determination of dissolved oxygen in water at mgL?1 levels, with modification in methodology for accurate detection of end point even at 10.0?gL?1 levels DO

P. Sahoo; R. Ananthanarayanan; N. Malathi; M. P. Rajiniganth; N. Murali; P. Swaminathan

2010-01-01

15

Potentiometric titration of long chain quaternary ammonium compounds using sodium tetraphenyl borate  

Microsoft Academic Search

Current methods for determining the activity of long chain quaternary ammonium compounds (QACS) are based either on dye partition,\\u000a titration, or colorimetric analysis. The two major disadvantages of these methods are the disparity of partition coefficients\\u000a among differently constituted QACS and the difficulty in detecting visual end points. Some potentiometric titration methods\\u000a for QACS have been reported in the literature.

C. N. Wanga; L. D. Metcalfea; J. J. Donkerbroek; A. H. M. Cosijn

1989-01-01

16

Titration of cyanide and hexacyanoferrate(II) with silver nitrate-I Calculation of titration curves for potentiometric and conductometric titration.  

PubMed

Stepwise potentiometric titration of cyanide and hexacyanoferrate(II) with silver nitrate is possible in the absence of potassium ions. At an initial concentration below 5.00 x 10(-4)M, cyanide can be titrated with silver nitrate (Ag:CN = 1:2) and the end-point indicated by precipitation of silver hexacyanoferrate(II); hexacyanoferrate(II) can be titrated with silver nitrate (Ag: Fe(CN)(6) = 4:1) and the end-point indicated by precipitation of silver dicyanoargentate. The hexacyanoferrate(II) reacts with silver to form two poorly soluble salts, Ag(4)Fe(CN)(6), KAg(3)Fe(CN)(6). The formation of these salts has been confirmed by conductometric titration of hexacyanoferrate(II) with silver nitrate in solutions containing varying concentrations of potassium nitrate. PMID:18962224

Asplund, J

1978-03-01

17

Surface Characteristics of Kaolinitic Clays and Clay-Humic Acid Complexes by Potentiometric and Conductometric Titrations  

Microsoft Academic Search

Acid and non-acid forms of kaolinite clays were found by potentiometric and conductometric titrations to possess a weak acid species, the concentration of which was increased by acidic preparation conditions and by the presence of soil organic matter bound to the clay. A stronger acid species was also found in untreated and in organic-free, HCl-treated samples (washed free of excess

N. C. Lockhart

1981-01-01

18

Determination of Hydrogen Fluoride and Uranium (VI) in Crude Uranium Hexafluoride by Hydrolysis and Potentiometric Titration  

Microsoft Academic Search

A simple method for determining HF and U(VI) in a hydrolyzed solution of UF6 by alkalimetry is described.About 1 g of UF6 was taken in a polytrifluoromonochloroethylene tube, and hydrolyzed with about 50 ml of water in a closed polyethylene bottle. Using a glass electrode, HF in the hydrolyzed solution was titrated potentiometrically with an alkali solution, after the U(VI)

Haruka SHINOHARA; Kimie IZAWA; Shigeo TSUJIMURA; Kenji MOTOJIMA

1967-01-01

19

Potentiometric titration of chloride in plant tissue extracts using the chloride ion electrode  

Microsoft Academic Search

Use of the chloride specific ion electrode to determine chloride in plants was evaluted. Direct potentiometric determination of chloride by the electrode resulted in unreproducible and extremely high chloride values. However, use of this electrode to indicate the end point in titration of the tissue?extract mixture with AgNO3 gave results nearly identical to those obtained by the Mohr procedure. The

R. L. LaCroix; D. R. Keeney; L. M. Walsh

1970-01-01

20

Back titration with mercuric ntrate in alkaline medium; potentiometric estimation of aluminium and manganese  

Microsoft Academic Search

Mercuric nitrate has been successfully used for back titrating excess EDTA amounts than required for chelation with Al3+ or Mn2+ ions. This principle was the basis underlying the potentiometric determination of small amounts of both metals in the range of 10 µg to ~ 6 mg. End points are attended within 0.01 to 0.02 ml of titrant with fair accuracy

H. Khalifa

1958-01-01

21

Semi-automatic version of the potentiometric titration method for characterization of uranium compounds.  

PubMed

The potentiometric titration method was used for characterization of uranium compounds to be applied in intercomparison programs. The method is applied with traceability assured using a potassium dichromate primary standard. A semi-automatic version was developed to reduce the analysis time and the operator variation. The standard uncertainty in determining the total concentration of uranium was around 0.01%, which is suitable for uranium characterization and compatible with those obtained by manual techniques. PMID:22406220

Cristiano, Bárbara F G; Delgado, José Ubiratan; da Silva, José Wanderley S; de Barros, Pedro D; de Araújo, Radier M S; Dias, Fábio C; Lopes, Ricardo T

2012-02-27

22

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

23

Simultaneous determination of equivalence volumes and acid dissociation constants from potentiometric titration data.  

PubMed

New iterative methods for analysis of potentiometric titration data of (a) mixtures of weak monoprotic acids with their conjugate bases, (b) solutions of polyprotic (di- and triprotic) acids, and (c) mixtures of two diprotic acids are presented. These methods, using data exclusively resulting from the acidic region of the titration curve permits the accurate determination of the analytical concentration of one or more acids even if the titration is stopped well before the end point of the titration. For the titration of a solution containing a conjugate acid/base pair, the proposed procedure enables the extraction of the initial composition of the mixture, as well as the dissociation constant of the concerned acid. Thus, it is possible by this type of analysis to distinguish whether a weak acid has been contaminated by a strong base and define the extent of the contamination. On the other hand, for the titration of polyprotic acids, the proposed approach enables the extraction of the accurate values of the equivalence volume and the dissociation constants K(i) even when the ionization stages overlap. Finally, for the titration of a mixture of two diprotic acids the proposed procedure enables the determination of the composition of the mixture even if the sum of the concentrations of the acids is not known. This method can be used in the analysis of solutions containing two diastereoisomeric forms of a weak diprotic acid. The test of the proposed procedures by means of ideal and Monte Carlo simulated data revealed that these methods are fairly applicable even when the titration data are considerably obscured by 'noise' or contain an important systematic error. The proposed procedures were also successfully applied to experimental titration data. PMID:18966298

Papanastasiou, G; Ziogas, I

1995-06-01

24

Determination of peroxyl radical scavenging activity of flavonoids and plant extracts using an automatic potentiometric titrator.  

PubMed

A novel potentiometric method for evaluation of peroxyl radical scavenging activity of flavonoids and plant extracts was developed. The oxidation of potassium iodide (KI) was performed in acetonitrilephosphate buffer (1:1) containing antioxidant using 2,2'-azobis(2-amidinopropane) dihydrochloride as a peroxyl radical generator. The amount of iodine released from KI during a 20-min free radical oxidation was determined quantitatively using an automatic potentiometric titrator with sodium thiosulfate. The radical scavenging activity of the sample was expressed as the inhibition ratio for iodine release of the control group mediated by the radical. The results obtained from some authentic polyphenols correlated well with those of previous reports. This is a simple, time-saving method requiring less than 30 min and is useful in assessing the radical scavenging activity of antioxidants in plant extracts. We describe the radical scavenging activities of various flavonoids including 21 kinds of tea catechins and vegetable extracts by this method. PMID:12720370

Sano, Mitsuaki; Yoshida, Risa; Degawa, Masakuni; Miyase, Toshio; Yoshino, Kyoji

2003-05-01

25

Potentiometric titrations of Bacillus subtilis cells to low pH and a comparison of modeling approaches  

Microsoft Academic Search

To provide constraints on the speciation of bacterial surface functional groups, we have conducted potentiometric titrations using the gram-positive aerobic species Bacillus subtilis, covering the pH range 2.1 to 9.8. Titration experiments were conducted using an auto-titrator assembly, with the bacteria suspended in fixed ionic strength (0.01 to 0.3 M) NaClO4 solutions. We observed significant adsorption of protons over the

Jeremy B. Fein; Jean-François Boily; Nathan Yee; Drew Gorman-Lewis; Benjamin F. Turner

2005-01-01

26

Charge determination of synthetic cationic polyelectrolytes by colloid titration  

Microsoft Academic Search

The stoichiometric interaction between oppositely charged polyelectrolytes forms the basis of the technique of colloid titration. This can be used, for instance, to determine the charge density of a cationic polyelectrolyte, using an anionic polyelectrolyte of known charge density, such as potassium polyvinyl sulphate (PPVS). The technique requires a suitable method of end-point detection and there are several possibilities. In

Sang-kyu Kam; John Gregory

1999-01-01

27

Protein-salt binding data from potentiometric titrations of lysozyme in aqueous solutions containing KCl  

SciTech Connect

An existing method for potentiometric titrations of proteins was improved, tested and applied to titrations of the enzyme hen-egg-white lysozyme in aqueous solutions containing KCl at ionic strengths from 0.1 M to 2.0 M at 25 C. Information about the protein`s net charge dependence on pH and ionic strength were obtained and salt binding numbers for the system were calculated using a linkage concept. For the pH range 2.5--11.5, the net charge slightly but distinctly increases with increasing ionic strength between 0.1 M and 2.0 M. The differences are most distinct in the pH region below 5. Above pH 11.35, the net charge decreases with increasing ionic strength. Preliminary calculation of binding numbers from titration curves at 0.1 M and 1.0 M showed selective association of chloride anions and expulsion of potassium ions at low pH. Ion-binding numbers from this work will be used to evaluate thermodynamic properties and to correlate crystallization or precipitation phase-equilibrium data in terms of a model based on the integral-equation theory of fluids which is currently under development.

Engmann, J.; Blanch, H.W.; Prausnitz, J.M. [Univ. of California, Berkeley, CA (United States). Dept. of Chemical Engineering]|[Lawrence Berkeley National Lab., CA (United States). Chemical Sciences Div.

1997-03-01

28

Determination of Glutamic Acid, Aspartic Acid, and Aminoacetic Acid by Potentiometric Titration Using a Cu exp 2+ -Sensitive Electrode.  

National Technical Information Service (NTIS)

This paper presents a volumetric determination of amino acids by potentiometric titration with CuSO sub 4 solution using PbS single-crystal electrode sensitve to Cu exp 2+ ions to indicate the endpoint. Analysis results for glutamic acid, aspartic acid an...

I. Haiduc M. Mioscu D. Cormos

1979-01-01

29

AN INVESTIGATION INTO THE FORMATION AND COMPOSITION OF AMMONIUM DIURANATE BY POTENTIOMETRIC TITRATION OF URANYL SALTS WITH AMMONIUM HYDROXIDE  

Microsoft Academic Search

Analysis of the product obtained by the precipitation of uranyl nitrate ; with ammonium hydroxide, in the Springfields process, indicated that its ; composition did not correspond to the formula (NHâ)âUâOâ, ; normally ascribed to it. The proportion of ammonium ion in the product was found ; to be less than the 5.77% required by this formula. By potentiometric titration

F. J. Armson; H. E. Dibben; H. Mason

1949-01-01

30

CHARACTERIZATION OF ASPHALTENES FROM SAUDI ARABIAN CRUDE OILS BY NONAQUEOUS POTENTIOMETRIC TITRATION AND ELEMENTAL ANALYSIS  

Microsoft Academic Search

Nonaqueous poientiometric titration was employed for the estimation of basic functionalities in the asphaltanes. A series of model basic compounds were titrated in a solvent mixture containing chlorobenzene and acetic anhydride. Perchloric acid in dioxane was used as the titrant. The model basic compounds were classified into very weak bases, weak bases and strong bases, based on their pKa (H2O)

Mohammad FarhatAli; Mohammad Saleem

1994-01-01

31

Effect of Fluoride, Chloride, Bromide, and Thiocynate on Potentiometric Titrations of Iron(II)-Tin(II) Mixtures with Cerium(IV).  

National Technical Information Service (NTIS)

A two-step curve is expected in the potentiometric titration of Fe(II)-Sn(II) mixtures with Ce(IV) in H sub 2 SO sub 4 . Each end point should indicate the respective oxidation of Sn(II) and Fe(II). However, experimentally only one end point was found; it...

Y. M. Kwok

1980-01-01

32

Phosphorus-doped and undoped glassy carbon indicator electrodes in controlled-current potentiometric titrations of bromide- or chloride-containing active ingredients in some pharmaceutical preparations.  

PubMed

Phosphorus-doped glassy carbon (as a novel material) and glassy carbon (Sigri commercial sample) were applied as potentiometric indicator electrodes in the titrimetric determination of active components with bromide or chloride in their molecules in different pharmaceutical preparations (Buscopan, Prostigmine, Isoptin, Bedoxin, Akineton and Trodon). After the necessary pre-treatment of the electrode surfaces and sample dissolution, the halide was titrated with a standard solution of silver nitrate (indirect determination). Amounts of 10-20 micromol of the investigated active ingredients per titration were determined with a relative standard deviation that, depending on the nature of indicator electrode, determined molecules and filler components, was in the range of 0.3-2.7%. The results obtained were compared with those of the official methods and with those obtained by potentiometric titrations using silver electrode. The titrimetric procedures developed are relatively fast, easy, economical and can be used to analyse of a large number of pharmaceutical products. PMID:15708666

Abramovi?, Biljana F; Guzsvány, Valéria J; Gaál, Ferenc F

2005-02-23

33

Determination of lead (II) in the presence of surfactants by potentiometric titration  

SciTech Connect

The purpose of the present paper is a study of the behavior of lead (II) in the presence of different surfactants with iodide ion as an accelerating agent and tetrabutylammonium as an inhibitor of the electrochemical process. The authors show that it is possible to determine potentiometrically with one polarized mercury steady-state electrode with satisfactory accuracy a (1-12) X 10/sup -5/ M solution of Pb(II) with a supporting electrolyte of an acetate buffer solution with pH 4.6 in the presence of tetrabutylammonium, KI, and the surfactants OP-7, OP-10, Syntanol, Syntegel, and Metaupon.

Vataman, I.I.; Khomenko, V.A.

1985-11-01

34

Potentiometric determination of weak bases by titration to a fixed pH value  

Microsoft Academic Search

The theoretical fundamentals of the pH-metric determination of weak bases by titration with solutions of strong acids to a\\u000a fixed pH value were considered. A simple and rapid procedure for determining ?-aminocaproic acid in medicinal preparations\\u000a was developed.

N. N. Golovnev; O. S. Romanova; N. V. Busygina

2000-01-01

35

An automated differential thermal and potentiometric titration apparatus for binding studies.  

PubMed

A differential pH-thermal titration apparatus is described which can detect pH differences with a sensitivity of +/- 0.0001 pH units and a thermal sensitivity of +/- 0.00002 degree C at a time constant of 0.1 s. With a reaction which yields 1 kcal mol-1, the current system can detect concentrations as low as 4 X 10(-6) M or, in a 2 ml volume, a total amount of 40 nmol. With a time constant of 0.1 s, the sensitivity is 20 +/- 4 micro degrees C. The experimental protocol is specified by a microprocessor and three modes of operation are possible: titration at constant rate of reagent addition, titration at variable rates of addition so that the contents of both cells are at either constant pH or at a constant temperature and variable rate when a rate of change is specified. Experimental data are collected in files, corrected for heat loss, initial baseline drift, and changes in volume. The final corrected data from the standardized run of 0.01338 M HCl in 0.2 M KCl at 25 degrees C calibrate the pH scale and yield the calorimetric conversion constants and pKw which are calculated and stored for subsequent corrections for the titration of an unknown acid or the measurement of binding constants and heats. PMID:3998380

Berger, R L; Cascio, H E; Davids, N; Gibson, C G; Marini, M; Thiebault, L

1985-03-01

36

Limitations of the potentiometric titration technique in determining the proton active site density of goethite surfaces  

NASA Astrophysics Data System (ADS)

Density of proton active surface sites at mineral surfaces is a property of fundamental importance in equilibrium modeling of surface complexation reactions. In this article, methods for an experimental determination of these sites at the surface of ?-FeOOH (goethite) are explored. It is shown that previously obtained saturation data of goethite with respect to protons do not yield a site density that can be considered as an intrinsic sorbent property: the results are below crystallographically expected values and values for different ionic media in terms of composition and concentration yield different numbers - for example, chloride would yield higher values than nitrate at the same concentration, and higher electrolyte concentration would favor higher apparent maxima. Although site saturation might be explained by electrostatic repulsion, which is more efficient at high electrolyte concentration or for certain ions, further independent experimental results show that no saturation occurs on goethite down to ph ? -log[H +] = 2.2 and possibly to ph = 1.0 in 0.6 M NaCl. For those very low pH values, the experimental charging curve was obtained by coulometric back titration (using the Gran plot) or titrations with tris (hydroxymethyl)-aminomethane of the supernatant of acidified goethite suspension. These experimental data are to our knowledge the first high quality data at such low pHs. However, small errors in the determination of proton concentrations (1%) are shown to strongly affect the shape of the charging curve for ph < 2. Furthermore, goethite dissolution (proton consumption and iron reduction in coulometric titrations) and liquid junction effects interfere at low ph, hampering the straightforward application of coulometric Gran titrations over the whole pH range. From these experiments, it can nonetheless be ascertained that a minimum of 2.5 protons/nm 2 can be adsorbed at the goethite surface from the point of zero charge (ph 9.4) to pH 0.9. Although these studies are restricted to goethite, those studies in which titrations with excess acid and base have been used for the determination of proton active site concentrations of sorbents should be reconsidered.

Lützenkirchen, Johannes; Boily, Jean-François; Lövgren, Lars; Sjöberg, Staffan

2002-10-01

37

Determination of uranium in uranium metal, uranium oxides, and uranyl nitrate solutions by potentiometric titration  

SciTech Connect

A simple, fast method for the determination of uranium in uranium metal, uranium oxides, and uranyl nitrate solutions has been adapted from the Davies-Gray volumetric method to meet the needs of Y-12. One-gram duplicate aliquots of uranium metal or uranium oxide are dissolved in 1:1 HNO/sub 3/ and concentrated H/sub 2/SO/sub 4/ to sulfur trioxide fumes, and then diluted to 100-mL volume. Duplicate aliquots are then weighed for analysis. For uranyl nitrate samples, duplicate aliquots containing between 50 and 150 mg of U are weighed and analyzed directly. The weighed aliquot is transferred to a Berzelius beaker; 1.5 M sulfamic acid is added, followed in order by concentrated phosphoric acid, 1 M ferrous sulfate, and (after a 30-second interval) the oxidizing reagent. After a timed 3-minute waiting period, 100 mL of the 0.1% vanadyl sulfate-sulfuric acid mixture is added. The sample is then titrated past its endpoint with standard potassium dichromate, and the endpoint is determined by second derivative techniques on a mV/weight basis.

Tucker, H.L.; McElhaney, R.J.

1983-01-01

38

The titrations of Asp-85 and of the cation binding residues in bacteriorhodopsin are not coupled.  

PubMed

An outstanding problem relating to the structure and function of bacteriorhodopsin (bR), which is the only protein in the purple membrane of the photosynthetic microorganism Halobacterium salinarium, is the relation between the titration of Asp-85 and the binding/unbinding of metal cations. An extensively accepted working hypothesis has been that the two titrations are coupled, namely, protonation of Asp-85 (located in the vicinity of the retinal chromophore) and cation unbinding occur concurrently. We have carried out a series of experiments in which the purple blue equilibrium and the binding of Mn2+ ions (monitored by electron spin resonance) were followed as a function of pH for several (1-4) R = [Mn2+]/[bR] molar ratios. Data were obtained for native bR, bR mutants, artificial bR and chemically modified bR. We find that in the native pigment the two titrations are separated by more than a pKa unit [delta pKa = pKa(P/B)-pKa(Mn2+) = (4.2-2.8) = 1.4]. In the non-native systems, delta pKa values as high as 5 units, as well as negative delta pKas, are observed. We conclude that the pH titration of cation binding residues in bR is not directly related to the titration of Asp-85. This conclusion is relevant to the nature of the high affinity cation sites in bR and to their role in the photosynthetic function of the pigment. PMID:10214967

Eliash, T; Ottolenghi, M; Sheves, M

1999-03-26

39

Diagrams of the formation of In2S3 and In2Se3 films on vitroceramic upon precipitation, according to potentiometric titration  

NASA Astrophysics Data System (ADS)

Boundary conditions and ranges of the formation of indium(III) sulfide and selenide upon precipitation by thiocarbamide and selenocarbamide are determined. Potentiometric titration of indium chloride (InCl3) in the concentration range of 0.0001 to 0.100 mol/L by a solution of sodium hydroxide is performed. It is found that the following pH ranges are optimal for In2S3 and In2Se3 film precipitation: from 3.0 to 4.5 and from 9.0 to 14.0. Indium selenide layers 100 to 300 nm thick are prepared on vitroceramic by hydrochemcial precipitation.

Tulenin, S. S.; Bakhteev, S. A.; Yusupov, R. A.; Maskaeva, L. N.; Markov, V. F.

2013-10-01

40

Acid–base properties of ion exchangers. I. Optimising of potentiometric titration of ion exchangers exemplified by carboxylic acid resins  

Microsoft Academic Search

The aim of this work was to determined conditions for fast titration the ion exchanger in the one-sample experiment allowing obtaining its equilibrium titration curve. Carboxylic acid ion exchangers KB-4 and Dowex MAC-3 were taken as examples. They were titrated under different conditions with NaOH, KOH and Ba(OH)2. The forward and backward titration of concentrated immersions of finely ground ion

V. S Soldatov; Z. I Sosinovich; T. A Korshunova; T. V Mironova

2004-01-01

41

Kinetics of bacterial potentiometric titrations: The effect of equilibration time on buffering capacity of Pantoea agglomerans suspensions  

Microsoft Academic Search

Several recent studies have made use of continuous acid–base titration data to describe the surface chemistry of bacterial cells as a basis for accurately modelling metal adsorption to bacteria and other biomaterials of potential industrial importance. These studies do not share a common protocol; rather they titrate in different pH ranges and they use different stability criteria to define equilibration

Leon Kapetas; Bryne T. Ngwenya; Alan M. Macdonald; Stephen C. Elphick

2011-01-01

42

Effect of fluoride, chloride, bromide, and thiocynate on potentiometric titrations of iron(II)-tin(II) mixtures with cerium(IV)  

SciTech Connect

A two-step curve is expected in the potentiometric titration of Fe(II)-Sn(II) mixtures with Ce(IV) in H/sub 2/SO/sub 4/. Each end point should indicate the respective oxidation of Sn(II) and Fe(II). However, experimentally only one end point was found; it corresponded to the total oxidation of Sn(II) and Fe(II). When this oxidation-reduction reaction was carried out in the presence of Cl/sup -/, the theoretical behavior was observed. The present study was done to ascertain if monovalent anions other than Cl/sup -/ have a similar effect on this oxidation-reduction system. The monovalent species F/sup -/, Br/sup -/, and SCN/sup -/ were selected for this study, and the results indicate that each affects the rate of reaction relative to the ease of oxidation of the individual ions.

Kwok, Y.M.

1980-07-31

43

Microcalorimetric and potentiometric titration studies on the adsorption of copper by P. putida and B. thuringiensis and their composites with minerals.  

PubMed

In order to have a better understanding of the interactions of heavy metals with bacteria and minerals in soil and associated environments, isothermal titration calorimetry (ITC), potentiometric titration and equilibrium sorption experiments were conducted to investigate the adsorption behavior of Cu(II) by Bacillus thuringiensis, Pseudomonas putida and their composites with minerals. The interaction of montmorillonite with bacteria increased the reactive sites and resulted in greater adsorption for Cu(II) on their composites, while decreased adsorption sites and capacities for Cu(II) were observed on goethite-bacteria composites. A gram-positive bacterium B. thuringiensis played a more important role than a gram-negative bacterium P. putida in determining the properties of the bacteria-minerals interfaces. The enthalpy changes (DeltaH(ads)) from endothermic (6.14 kJ mol(-1)) to slightly exothermic (-0.78 kJ mol(-1)) suggested that Cu(II) is complexed with the anionic oxygen ligands on the surface of bacteria-mineral composites. Large entropies (32.96-58.89 J mol(-1) K(-1)) of Cu(II) adsorption onto bacteria-mineral composites demonstrated the formation of inner-sphere complexes in the presence of bacteria. The thermodynamic data implied that Cu(II) mainly bound to the carboxyl and phosphoryl groups as inner-sphere complexes on bacteria and mineral-bacteria composites. PMID:20576350

Fang, Linchuan; Cai, Peng; Li, Pengxiang; Wu, Huayong; Liang, Wei; Rong, Xingmin; Chen, Wenli; Huang, Qiaoyun

2010-05-31

44

Application of the finite element simulation method to the adiabatic and potentiometric corrections of calorimetric titration data.  

PubMed

A general numerical analysis procedure is described which has been applied to an automated differential pH-thermal titration apparatus operated isoperibolically to obtain thermal corrections for heat loss. It is based on the Direct Byte (D-B) finite element computer simulation technique (FEST) applied to the heat conduction behavior of the instrument with time. Thermal constants of the numerical model are determined, and the results of the correction for titration data obtained from acid-base runs show that a constant upper baseline is achieved using this technique for both fast and slow reactions to an accuracy of 2%. The method is equally valid for endothermic and exothermic reactions. PMID:3998381

Davids, N; Berger, R L; Marini, M A

1985-03-01

45

An online computer method for the potentiometric titration of mixtures of a strong and a weak acid  

Microsoft Academic Search

A PDP-11 online computer method for the titration of mixtures or a strong and a weak acid is described.The method is based on multiparametric curve-fitting. One or the parameters found from the calculations is the dissociation constant of the weak acid, hence the method can be applied even when this constant is unknown. Accurate results (relative error ±1%) were obtained

M. Bos

1977-01-01

46

Copper redox transformation and complexation by reduced and oxidized soil humic Acid. 2. Potentiometric titrations and dialysis cell experiments.  

PubMed

Cation binding and electron transfer reactions of humic substances determine copper speciation in redox-dynamic systems, but quantitative studies for Cu(+) binding to humic substances are lacking. We investigated reduction of Cu(2+) and binding of Cu(+) at pH 7.0 in a dialysis cell experiment using reduced and reoxidized soil humic acid (HA) as reductant and sorbent at copper loadings of 9.5-600 mmol kg(-1). The data were used to quantitatively explain the interaction between cation binding and electron transfer processes that determine copper speciation in the presence of HA under anoxic and oxic conditions. Addition of Cu(2+) to reduced HA resulted in almost complete reduction to Cu(I) within 1 h. Reduction was also significant under oxic conditions. The slow decrease of the Cu(I) fraction was attributed to formation of Cu(0) based on thermodynamic consideration. Cu(+) binding to HA was found to be strong compared to other chalcophile cations like Ag(+) or Cd(2+). Our results indicate that Cu(+) and Cu(2+) isotherms exhibit a redox potential-dependent intersection point. According to the differences in Cu(+) and Cu(2+) binding, the presence of HA was found to extend the stability field of Cu(II) to moderately reducing conditions and to reduce the stability field of Cu(0) due to the formation of Cu(I) complexes. PMID:24050604

Maurer, Felix; Christl, Iso; Fulda, Beate; Voegelin, Andreas; Kretzschmar, Ruben

2013-09-19

47

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

2007-10-13

48

Titration kinetics of Asp85 in bacteriorhodopsin: exclusion of the retinal pocket as the color-controlling cation binding site  

Microsoft Academic Search

The spectrum (the purple?blue transition) and function of the light-driven proton pump bacteriorhodopsin are determined by the state of protonation of the Asp-85 residue located in the vicinity of the retinal chromophore. The titration of Asp-85 is controlled by the binding\\/unbinding of one or two divalent metal cations (Ca2+ or Mg2+). The location of such metal binding site(s) is approached

X Fu; S Bressler; M Ottolenghi; T Eliash; N Friedman; M Sheves

1997-01-01

49

Potentiometric microdetermination of oxiranes  

Microsoft Academic Search

Summary A potentiometric microtitration for the determination of high molecular weight oxiranes is presented. It is based on the reaction of oxiranes with quaternary ammonium bromide and titration with 0.01N perchloric acid. The preferred solvent is acetic acid although small amounts of toluene or chloroform may be used. Epoxy equivalents as high as 370,000 have been determined.

Walter Selig

1980-01-01

50

The determination of the stability constants of complexes of 1,2,4-triazoles and biologically relevant ligands with M(II) by potentiometric titration in aqueous solution  

Microsoft Academic Search

Potentiometric equilibrium measurements have been performed at 25?±?0.1°C and I?=?0.10?mol dm NaNO3 for the interaction of 1,2,4-triazole and M(II) [Cu, Co, Ni, and Zn] with some biologically important ligands (glycine, ?-alanine, DL-valine, n-valine, DL-leucine, serine, aspartic acid, histidine, and asparagine). Ternary complexes are formed by a stepwise mechanism. The relative stabilities of the ternary complexes are compared with those of

Mohamed Magdy Khalil; Rehab Mahmoud; Mahmoud Moussa

2012-01-01

51

Adsorption of RNase A on cationic polyelectrolyte brushes: a study by isothermal titration calorimetry.  

PubMed

We present a study of the adsorption of a positively charged protein to a positively charged spherical polyelectrolyte brush (SPB) by isothermal titration calorimetry (ITC). ITC is used to determine the adsorption isotherm as a function of temperature and of salt concentration (at physiological pH 7.2). At low ionic strength, RNase A is strongly adsorbed by the SPB particles despite the fact that both the SPB particles and the protein are positively charged. Virtually no adsorption takes place when the ionic strength is raised through added salt. This is strong evidence for counterion release as the primary driving force for protein adsorption. We calculated that ~2 counterions were released upon RNase A binding. The adsorption of RNase A into like-charged SPB particles is entropy-driven, and protein protonation was not significant. Temperature-dependent measurements showed a disagreement between the enthalpy derived via the van't Hoff equation and the calorimetric enthalpy. Further analysis shows that van't Hoff analysis leads to the correct enthalpy of adsorption. The additional contributions to the measured enthalpy are potentially sourced from unlinked equilibria such as conformational changes that do not contribute to the binding equilibrium. PMID:21970466

Becker, Alisa L; Welsch, Nicole; Schneider, Christian; Ballauff, Matthias

2011-10-14

52

A potentiometric study of acid–base equilibria of substituted pyridines in acetonitrile  

Microsoft Academic Search

Acid dissociation, as well as cationic homo- and heteroconjugation equilibria have been studied by potentiometric titration for pyridine and a variety of its mono- and di-substituted derivatives in the polar protophobic aprotic solvent, acetonitrile. The heteroconjugation equilibria were investigated in several BH+\\/B1 systems without proton transfer in which the pKa values of the protonated form of the proton acceptor were

D. Augustin-Nowacka; L. Chmurzyñski

1999-01-01

53

Graphic determination of equivalence volumes in potentiometric titrations of mixtures of weak acids-II Titration of a dibasic acid and determination of its two acid species H(2)A and HA(-).  

PubMed

The method given in part I is used to determine the mixed stability constants of a dibasic acid. Values of log K(H)(HA(2)) = 2.878 and log K(H)(HA(2)) = 4.011 for tartaric acid and 4.077 and 5.335 for succinic acid at mum = 0.1 and T = 25 degrees have been obtained. The method is also applied to titrations of these acids, the error obtained being about 0.5 %, and to titrate a mixture of tartaric acid and potassium hydrogen tartrate with an error of 0.7-1.6% PMID:18961580

Ivaska, A

1974-11-01

54

Use of pH electrode for precipitation titration analysis: Theory and practice  

Microsoft Academic Search

A theoretical model for the potentiometric analysis of precipitation titrations using a pH electrode has been developed and\\u000a tested. The new analytical method is possible by introducing a mediator which must be a weak acid and must be able to form\\u000a an insoluble salt with a cation (a titrant). Theoretical expressions of pH, as well as the concentrations of all

T.-K. Hong; B.-H. Koo; S.-Y. Ly; M.-H. Kim; M.-Z. Czae

2009-01-01

55

NEW CATION EXCHANGE RESINS BASED ON POLYVINYL ALCOHOL CONTAINING CARBOXYL GROUPS FOR THE REMOVAL OF SOME TEXTILE CONTAMINANTS FROM AQUEOUS SOLUTIONS  

Microsoft Academic Search

Two cation exchange resins having carboxyl contents, 628 and 424 meq\\/100 g sample were prepared by free radical polymerization of acrylic acid in presence of polyvinyl alcohol aqueous solution using methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator. The prepared resins were characterized by investigation of their potentiometric titration, durability, water solubility, and swellability. The removal of Cu ions (in

H. M. Fahmy; Z. El-Sayed

2002-01-01

56

Formation quotients of aluminum sulfate complexes in NaCF3SO3 media at 10, 25, and 50 degrees C from potentiometric titrations using a mercury/mercurous sulfate electrode concentration cell.  

PubMed

Mercury/mercurous sulfate electrode concentration cells (with liquid junction) are employed in this study to determine the formation constants of aluminum sulfate complexes, with the principal advantage that the change in the free sulfate concentration is measured directly without the need to know the standard potential of the electrode. Potentiometric titrations were conducted at temperatures of 10, 25, and 50 degrees C and ionic strengths of approximately 0.3, 0.5, and 1.0 molal in aqueous solutions of the inert 1:1 electrolyte sodium trifluoromethanesulfonate (NaTr). Stoichiometric molal formation quotients Q1 and Q2, respectively, for the reactions Al3+(aq) + SO4(2-)(aq) AlSO4+(aq) and Al3+(aq) + 2SO4(2-)(aq) <= >Al(SO4)2-(aq) were determined. The values of log Q1 obtained from this work in NaTr media at ionic strengths of 0.3 and 1.0 mol x kg(-1) and 50 degrees C (1.72 +/- 0.08 and 1.35 +/- 0.06, respectively) are in excellent agreement with the values (1.71 +/- 0.2 and 1.32 +/- 0.1) determined in NaCl media from the recent potentiometric study conducted in the same laboratory using a hydrogen electrode concentration cell by Ridley et al. (Ridley, M. K.; Wesolowski, D. J.; Palmer, D. A.; Kettler, R. M. Geochim. Cosmochim. Acta 1999, 62, 459-472). The value of log Q2 (2.05 +/- 0.05) in 1.0 mol x kg(-1) from this work is smaller than the value reported by Ridley et al. (2.6 +/- 0.5) but within the combined experimental error. Empirical isothermal equations are presented to permit calculation of the equilibrium quotients as a function of ionic strength (0-1 mol x kg(-1)), giving log K1 and log K2 values at 25 degrees C and infinite dilution of 3.84 +/- 0.12 and 5.58 + 0.09, respectively. The value for log K1 obtained in this study at 25 degrees C is bracketed within experimental uncertainty by values reported by Kryzhanovskii et al. (Kryzhanovskii, M. M.; Volokhov, Y. A.; Pavlov, L. N.; Eremin, N. I.; Mironov, V. E Zh. Prikl. Khim. 1971, 44,476-479) and Nishide and Tsuchiya (Nishide, T.; Tsuchiya, R. Bull. Chem. Soc. Jpn. 1965, 38, 1398-1400), namely, 3.89 and 3.73, respectively. All other literature values for the first aluminum sulfate association constant are considerably lower than these results, which is also true for the second association constant, although there are few experimental data available for the latter. Empirical equations are also presented for calculating values of log Q1 and log Q2 from 0 to 1 molal ionic strength and from 10 to 125 degrees C, spanning the range of most environmental conditions at which these reactions are important. PMID:11827050

Xiao, Caibin; Wesolowski, David J; Palmer, Donald A

2002-01-15

57

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

58

Precipitation titration of perchlorate using new titrants  

SciTech Connect

We have evaluated the following new titrants for the potentiometric precipitation titration of perchlorate: cetyltrimethylammonium chloride (CETAC), cetyltrimethylammonium bromide (CETAB), cetylpyridinium chloride (CPC), and benzyldimethyltetradecylammonium chloride (BDTAC). Titrations were monitored with a fluoroborate ion-selective electrode (ISE) and a double-junction reference electrode. The titration system was controlled by a Tektronix 4051 graphics system. The perchlorate, nitrate, and calcium ISE may also be used to monitor emf's. 7 tables, 2 figures.

Selig, W.

1980-05-01

59

Determination of Free Acid in the Presence of Hydrolysable Cations by the Use of Titration and Mathematical Derivatives.  

National Technical Information Service (NTIS)

The aim of the project described here was the development of an accurate method for the determination of free acid in the presence of hydrolysable cations. At present, no accurate methods are available for this determination. The difficulty with this dete...

E. H. R. Von Barsewisch R. A. Hasty

1985-01-01

60

A Study of the Precise Determination of Macroamounts of Plutonium in Solution by Three Electrometric Oxidation - Reduction Titration Methods.  

National Technical Information Service (NTIS)

The precise determination of macroamounts of plutonium in solution has been studied by two potentiometric and one amperometric titration method. The potentiometric methods were, within the limits of experimental error, without bias, but the results obtain...

L. H. Andersson E. B. Bauren E. Helleday

1970-01-01

61

Estimation of composition, coordination model, and stability constant of some metal\\/phosphate complexes using spectral and potentiometric measurements  

Microsoft Academic Search

Complexation reactions in a binary metal\\/phosphate system were studied. Protolytic equilibria of phosphate in the presence\\u000a of cobalt, nickel, iron, copper, chromium and silver metal ions were investigated by potentiometric titrations in the pH range\\u000a of 2–11. Stability constants of the metal\\/phosphate complexes were determined by computer analysis of the potentiometric titration.\\u000a Potentiometric titrations suggest that the presence of metal

Khalid Abu-Shandi; Fadel Al-Wedian

2009-01-01

62

Zur potentiometrischen Titration von Phenolen in Gegenwart von Äthylenoxidaddukten  

Microsoft Academic Search

The potentiometric titration of phenols with sodium hydroxide solution has been made possible by addition of ethoxylated nonylphenol, as the dissociation constants of the complexes formed are considerably greater than those of the phenols.

K. H. Mohr; F. Wolf

1967-01-01

63

The titration of clay minerals I. Discontinuous backtitration technique combined with CEC measurements.  

PubMed

Previous experimental studies on clay potentiometric titration have been unable to distinguish inorganic cation exchange in the interlayer and on basal plane surfaces from specific pH-dependent sorption of cations and anions on the edges. In this study, we refined a titration technique, combining discontinuous backtitration and cation exchange capacity (CEC) measurements, and applied it to the potentiometric titration of Na- and Ca-conditioned montmorillonites. This technique can be used to accurately measure cation exchange, edge surface proton charge, dissolution of clay, and precipitation of new phases. Thus, a precise measurement of the variations of net proton surface charge is possible. This has important implications for clay surface modeling (see part II of this article) and for processes that depend on the clay surface charge, e.g., alteration, rheological processes, and contamination retention applications. In addition, this study confirms the adsorption of ionic pairs such as CaCl+ in exchange site positions and shows that CaOH+ could behave like CaCl+. This result, together with the evidence of precipitation of a Ca?Si phase over a short time-scale (1 week) at high pH and low temperature, can be used to model clay-concrete interactions more accurately. We confirmed and quantified the H+/Na+ exchange reaction at low pH. Finally, we demonstrate that both the edge surface charge and the permanent structural charge are compensated for by the nonspecific sorption of cations from solution across the entire pH range from 4 to 11. Under these conditions, the surface potential is fully screened and does not need to be invoked in modeling sorption processes on clay particles in dilute suspensions. PMID:15051456

Tournassat, Christophe; Greneche, Jean-Marc; Tisserand, Delphine; Charlet, Laurent

2004-05-01

64

Surface Titrations of Perlite Suspensions  

Microsoft Academic Search

The surface charge behaviour of unexpanded and expanded perlite samples in KNO3and NaCl solutions were investigated as a function of pH and ionic strength. The solutions of KNO3and NaCl ranging from 10?3to 1.0Mwere used. The potentiometric titration method was used to determine the surface charge of perlite samples. It was confirmed that the perlite samples had no the point of

Mahir Alkan; Mehmet Do ?

1998-01-01

65

Ionometric determination of quaternary ammonium cations in industrial extraction reagents and sewage  

SciTech Connect

When extraction reagents based on salts of quaternary ammonium bases (QAS) are used in the technology of purification of rare earth elements (REE), the problem arises of determining QAS in technological and dilute aqueous solutions (circulating waters and sewage). A direct method of determining cations of QAS is known, based on the use of ion-selective electrodes, reversible to hydrophobic cations. Two types of procedures can be distinguished within the framework of this method: potentiometric titration and direct potentiometry. In this work the authors discuss the possibilities of both types for practical use in industrial analysis.

Kokovkin, V.V.; Nemirovskii, A.M.; Kravchenko, L.Kh.; Smolyakov, B.S.

1988-01-01

66

Effect of water content in perchloric acid on the non-aqueous potentiometric titration of nitrogen-containing compounds 1 This work was presented, in part, at the Pittsburgh Conference, Chicago, IL, 1996. 1  

Microsoft Academic Search

In the United States Pharmacopeia (USP), 0.1 N perchloric acid in acetic acid volumetric solution (hereafter HClO4 VS) used for non-aqueous titration has specified a water content between 0.02 and 0.05%. Preparing this titrant with such a narrow range of water content is very time consuming, precludes the use of commercially available titrants, and, consequently, prompted an investigation to try

Xiaohe S Qi; R Brent Miller; Yoshihiro Namiki; John Zhang; Robert Jacobus

1997-01-01

67

Competitive Potentiometric Study of a Series of 18-crown-6 with Some Alkali and Alkaline Earth Metal Ions in Methanol Using an Ag + \\/Ag Electrode  

Microsoft Academic Search

The complexation of some alkali and alkaline earth cations with18-crown-6(18C6), dibenzo-18-crown-6 (DB18C6), dicyclohexyl-18-crown-6 (DCY18C6), and dibenzopyridino-18-crown-6 (DBPY18C6) in a methanol solution has been studied by a competitive potentiometric titration using Ag+\\/Ag electrode as a probe. The stoichiometry and stability constants of the resulting complexes have been evaluated by the MINIQUAD program. The stoichiometry for all resulting complexes was 1:1. The

Javad Zolgharnein; Hoomayon Tahmasebi; Morteza Habibi; Saeid Amani

2004-01-01

68

Studies on the complexation of Pr(III) and Nd(III) with glycyl-glycine (gly-gly) using spectral analysis of 4f-4f transitions and potentiometric titrations  

NASA Astrophysics Data System (ADS)

The interaction of gly-gly with Pr(III) and Nd(III) have been studied in different aquated organic solvents like CH3OH, CH3CN, dioxane and DMF by using 4f-4f transitions spectra. Various energy interaction parameters like Slater Condon (Fk), Racah (Ek), Lande (?4f), nephelauxetic effect (?), bonding (b1/2) and percent covalency (?) parameters have been calculated to explain the nature of complexation. The intensity parameters like oscillator strength (P) and Judd-Ofelt parameters (T?, ? = 2, 4, 6) also support the mode of binding of gly-gly to metal ions. The results show that Pr(III) and Nd(III) with gly-gly form complexes by ionic linkages with carboxylate anion with weak covalency. The protonation constants and metal-ligand stability constants have also been determined by potentiometric measurements in aqueous medium at different temperatures (290, 300 and 310 K) at constant ionic strength, 0.1 mol dm-1. The results show the formation of metal-ligand complexes in the stoichiometric ratio 1:1. The stability of complexes is more in Nd(III) complexes as compared to Pr(III) complexes. Thermodynamic parameters (?G, ?H and ?S) of complexes were also calculated and the negative values of ?G and ?H show that the complex reactions are spontaneous and exothermic. The positive values of ?S indicate high stability of complex reactions which are enthalpy-driven.

Ranjana Devi, N.; Huidrom, Bimola; Rajmuhon Singh, N.

2012-10-01

69

A new potentiometric method for the estimation of vanadium  

Microsoft Academic Search

A new potentiometric method is given for the accurate determination of small amounts of vanadium after reduction to the 4-valent state, involving back-titration of an added excess of EDTA by mercuric solution. The fact that 5-valent, but not 4-valent, vanadium has no influence on the course of the back-titration of excess EDTA with mercuric ions was used in the analysis

H. Khalifa; A. El-Sirafy

1967-01-01

70

Protamine titration.  

PubMed

Protamine titration is the gold standard method for the measurement of unfractionated heparin (UFH) concentration in plasma. Protamine titration produces reliable and reproducible results; however it is -generally not considered a convenient assay for current clinical management of UFH as it is not readily automated (Olson et al. Arch Pathol Lab Med 122(9):782-798, 1998). Early clinical trials of UFH therapy determined that a heparin concentration of 0.2-0.4 U/ml by protamine titration correlated to an APTT of 1.5-2.5 times higher compared to baseline values produced desirable UFH safety and efficacy outcomes (Hull et al. N Engl J Med 315(18):1109-1114, 1986; Hull et al. N Engl J Med 322:1260-1264, 1990; Turpie et al. N Engl J Med 320:352-357, 1989; Brill-Edwards et al. Ann Intern Med 119(2):104-109, 1993; Hull Int Angiol 14(1):32-34, 1995). Such studies paved the way to the current view that it is no longer ideal to manage UFH based solely upon a 1.5-2.5 times prolongation of the "normal" APTT. Most advisory bodies recommend therapeutic APTTs be determined by correlating APTT results with therapeutic UFH levels as measured by anti-Xa assay (0.35-0.7 U/ml) or protamine titration (0.2-0.4 U/ml) (Hirsh and Raschke. Chest 126(3):188S-203S, 2004) (see Note 1). The concentration of UFH in a sample is measured by determining the amount of protamine required to return the thrombin clotting time (TCT) test (prolonged by UFH) to a pre-UFH level (Laffan and Manning. Dacie and Lewis: practical haematology. Churchill Livingstone: London, 2001). PMID:23546721

Newall, Fiona

2013-01-01

71

A study of the effect of proteins and endogenous cations on a lipophilic ?-cyclodextrin-based potentiometric lidocaine sensor using discrete solution and flow-injection analysis  

Microsoft Academic Search

2,6 Didodecyl ? cyclodextrin (2,6dd?CD) modified ion-selective electrodes (ISEs) were used in discrete solutions and in a flow injection analysis manifold for monitoring the local anaesthetic lidocaine hydrochloride (lignocaine) in the presence of endogenous cations and proteins. Membrane matrices comprised of either high molecular weight poly (vinyl chloride) (PVC) or polyurethane (Tecoflex SG 80) were compared. The behaviour of these

Ritu Kataky; Klara Toth; Simon Palmer; Zsofia Feher

1999-01-01

72

Rapid determination of the equivalence volume in potentiometric acid-base titrations to a preset pH-II Standardizing a solution of a strong base, graphic location of equivalence volume, determination of stability constants of acids and titration of a mixture of two weak acids.  

PubMed

A newly proposed method of titrating weak acids with strong bases is applied to standardize a solution of a strong base, to graphic determination of equivalence volume of acetic acid with an error of 0.2%, to calculate the stability constants of hydroxylammonium ion, boric acid and hydrogen ascorbate ion and to analyse a mixture of acetic acid and ammonium ion with an error of 0.2-0.7%. PMID:18961474

Ivaska, A

1974-06-01

73

The titration of clay minerals II. Structure-based model and implications for clay reactivity.  

PubMed

The potentiometric titration and CEC data presented in part I are modeled in this paper, part II. Two models are compared: the two pK, three complexation sites plus exchange sites nonelectrostatic model developed by Baeyens and Bradbury and a model based on the MUSIC approach developed by Hiemstra and Van Riemsdijk. Both morphological and structural information is used to develop this new model. Morphological information is taken from the literature, while structural information is taken from the literature and constrained by supporting FTIR experiments. The Baeyens and Bradbury model is found to reproduce the general tendency of the titration curve, whereas the model based on the Hiemstra and Van Riemsdijk MUSIC approach provides a better fit to the experimental data. The former uses only 3 edge reaction sites, whereas the latter uses at least 27 edge reaction sites. Five main reactive sites are sufficient to fit the MUSIC model curve, but the model allows us to derive the properties of 22 other reactive sites. Logically, the greater the number of sites, the better the fit. Nevertheless, fewer adjustable parameters are necessary for the Hiemstra and Van Riemsdijk MUSIC model than for the Baeyens and Bradbury model, thanks to structural and morphological constraints. The precision of the potentiometric titration curve is insufficient to verify that the properties of the 27 sites given by the MUSIC model are effective. Thus, we coupled some properties of clay minerals, such as dissolution, to the modeled acid-base properties of these sites to assess our model. We then questioned the ability of simplified models such as the Baeyens and Bradbury model to predict the interactions between clay minerals and solutions in natural environments. In addition, we derived the cation exchange selectivity coefficients for CaCl+ ionic pairs and H+ from our CEC data and gave an estimate for the CaOH+ selectivity coefficient. PMID:15051457

Tournassat, Christophe; Ferrage, Eric; Poinsignon, Christiane; Charlet, Laurent

2004-05-01

74

Aqueous shift reagents for high-resolution cation NMR. VI. Titration curves for in vivo 23Na and 1H2O MRS obtained from rat blood.  

PubMed

Frequency shift/concentration calibration curves applicable to the use of shift reagents (SRs) for in vivo 23Na MRS studies can be obtained from experiments with whole blood. Here, they are reported for titrations of rat blood with the SRs DyTTHA3- and TmDOTP5-. There are a number of considerations that must be made in order to derive accurate calibration curves from the experimental data. These include the effects of bulk magnetic susceptibility (BMS, since the SRs are paramagnetic), the effects of water flux (since addition of the SR stock solution to blood renders the plasma hyperosmotic), and the consequences of restricted distribution of the SR anion in the erythrocyte suspension. We give in some detail the BMS shift theory that obtains in this case and show also how it applies to excised perfused organ as well as in vivo studies. Also, we report significant effects of adjuvant Ca2+ additions in the TmDOTP5- titrations. These are very important to the successful use of this SR in vivo. Finally, our considerations of BMS lead naturally to an understanding of its manifestations in the shifts of the 1H2O resonance frequencies of cell suspensions and tissues induced by SRs. Since these are being increasingly reported, and often misinterpreted, we devote an experiment and some discussion to this subject. We show that this phenomenon cannot be used to quantitatively discriminate intra- and extracellular 1H2O signals. PMID:8457429

Albert, M S; Huang, W; Lee, J H; Balschi, J A; Springer, C S

75

Complexation of lithium ion by the cryptand 4,7,13-trioxa-1,10-diazabicyclo(8. 5. 5)eicosane (C21C sub 5 ) in a range of solvents. A sup 7 Li nuclear magnetic resonance and potentiometric titration study  

SciTech Connect

Complexation of Li{sup +} by the cryptand 4,7,13-trioxa-1,10-diazabicyclo(8.5.5)eicosane (C21C{sub 5}) to form the cryptate (Li.C21C{sub 5}){sup +} has been studied in eight solvents by {sup 7}Li NMR and potentiometric titration methods. The variation of the {sup 7}Li chemical shift of (Li.C21C{sub 5}){sup +} with solvent and a comparison of its stability with those of other cryptates indicate that (LiC21C{sub 5}){sup +} exists substantially in the exclusive form in solution in contrast to the inclusive form adopted in the solid state. The exchange of Li{sup +} on (Li.C21C{sub 5}){sup +} is within the {sup 7}Li NMR time scale in methanol, dimethylformamide, diethylformamide, and dimethylacetamide, where, in the last solvent at 298.2 K, the logarithm of the (Li.C21C{sub 5}){sup +} stability constant (log (K/dm{sup 3}mol{sup {minus}1})) is 1.85 and the decomplexation kinetic parameters are k{sub d} = 237 {plus minus} 4 s{sup {minus}1}, {Delta}H{sub 3}{double dagger} = 49.0 {plus minus} 2.1 kJ mol{sup {minus}1}, and {Delta}S{sub d}{double dagger} = {minus}35.0 {plus minus} 2.8 J K{sup {minus}1} mol{sup {minus}1}. Similar data are obtained in the other three solvents. In acetonitrile, propylene carbonate, and acetone, Li{sup +} exchange is too slow to be studied by {sup 7}Li NMR spectroscopy. The (Li.C21C{sub 5}){sup +} data are compared with those for (Li.C211){sup +}, (Na.C21C{sub 5}){sup +}, and (Na.C211){sup +}. 29 refs., 4 figs., 4 tabs.

Lincoln, S.F.; Abou-Hamdan, A. (Univ. of Adelaide, South Australia (Australia))

1990-09-05

76

The reaction of C -phenylcalix[4]resorcinarene-based polymer with quaternary ammonium and potassium cations  

Microsoft Academic Search

The resol polycondensation ofC-phenylcalix[4]resorcinarene with formaldehyde affords a corss-linked polymer possessing ion-exchange ability. The ion-exchange\\u000a capacity of the polymer with respect to NH4\\u000a +, Me4N+, Et4N+, Bu4N+, and K+ cations was determined. The equilibrium in the systemsC-phenylcalix[4]resorcinarene-based polymer—binary or ternary aqueous solutions of electrolytes was studied by potentiometric\\u000a titration and quantumchemical MNDO\\/PM3 calculation

G. N. Al'tshuler; O. N. Fedyaeva; E. V. Ostapova

2000-01-01

77

Potentiometric determination of anhydrous aluminum chloride  

SciTech Connect

Anhydrous aluminum chloride is a strong Lewis acid, widely used as a catalyst, in the synthesis and analysis of organic products. The aim of this article is to develop a potentiometric method of determining anhydrous AlCl/sub 3/. To estimate the validity of the results of the determination, use was made of French, Japanese, and Soviet samples of AlCl/sub 3/ with a known content of the main substance. The titration was performed in ethylene glycol. The procedure makes it possible to investigate the activity of AlCl/sub 3/ as a catalyst in different organic solvents

Kofman, A.G.; Chernysh, G.V.; Vorozhtsov, G.N.

1987-12-20

78

Permian Potentiometric Analysis.  

National Technical Information Service (NTIS)

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 ...

J. L. Devary

1983-01-01

79

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

80

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

81

Potentiometric titration of poly(?-D)galacturonic acid  

Microsoft Academic Search

A commercially available sample of poly(?-D)galacturonic acid, i.e. pectic acid, was characterized according to the size and shape of its molecule through the volumetric and transport properties of its aqueous solutions. Thus, the average molecular weight of polygalacturonic acid and its average degree of polymerization were estimated on the basis of viscosity measurements. The length-to-diameter ratio, calculated by means of

D. Rudan-Tasi?; C. Klofutar

1996-01-01

82

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

83

Potentiometric microtitration of anions with quaternary ammonium halides  

Microsoft Academic Search

Summary Cetyltrimethylammonium bromide has been evaluated for the potentiometric precipitation titration of some water-soluble organic anions. Emf's were monitored with a fluoroborate ion-selective electrode and a double-junction reference electrode. The perchlorate, nitrate, and calcium electrodes also respond to the various anions. Cetyltrimethylammonium chloride and cetylpyridinium chloride are also suitable as titrants for the various anions. They can be used also

Walter Selig

1979-01-01

84

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

85

Association quotients of aluminum sulphate complexes in NaCl media from 50 to 125°C: Results of a potentiometric and solubility study  

Microsoft Academic Search

The speciation and molal formation quotients for the complexation of aluminum with sulphate were measured based on potentiometric and solubility experiments. Potentiometric titrations, utilizing a hydrogen-electrode concentration cell, were performed from 50 to 125°C at ionic strengths of 0.1, 0.3 and 1.0 molal in aqueous NaCl media. Two aluminum-sulphate species, AlSO4+and Al(SO4)2?, were identified from the titration data and the

Moira K. Ridley; David J. Wesolowski; Donald A. Palmer; Richard M. Kettler

1999-01-01

86

Chemically modified carbon paste electrode for the potentiometric determination of dicylomine hydrochloride in batch and in FIA conditions.  

PubMed

A carbon-paste electrode for dicyclomine hydrochloride (DcCl) was prepared and fully characterized in terms of composition, life span, usable pH range and temperature. The electrode was applied to the potentiometric determination of dicylominium ion in its pure state and in pharmaceutical preparations in batch and flow injection conditions and in biological fluids using standard additions method. The electrode is based on a mixture of two ion-exchangers, namely, dicyclominium-phosphomolybdate and dicylominium-tetraphenylborate, dissolved in dioctyl phthalate as pasting liquid. The modified electrode showed a near-Nernstian slope of 58 +/- 2 mV over the concentration range of 1.2 x 10(-5)-1.6 x 10(-2) M with an average recovery of 97-102% and a RSD of 0.090-1.00. The electrode exhibits good selectivity for DcCl with respect to a large number of inorganic cations, sugars, amino acids and organic substances of biological fluids. Potentiometric titrations of DcCl with several titrants have been monitored using this modified carbon paste electrode as an end-point indicator electrode. PMID:15228109

Ibrahim, H; Issa, Y M; Abu-Shawish, Hazem M

2004-06-01

87

Potentiometric Determination of Ketotifen Fumarate in Pharmaceutical Preparations and Urine Using Carbon Paste and PVC Membrane Selective Electrodes  

PubMed Central

This study compares between unmodified carbon paste (CPE; the paste has no ion pair) and polyvinyl chloride (PVC) membrane selective electrodes that were used in potentiometric determination of ketotifen fumarate (KTF), where sodium tetraphenylborate (NaTPB) was used as titrant. The performance characteristics of these sensors were evaluated according to IUPAC recommendations which reveal a fast, stable, and linear response for KTF over the concentration range of 10?7 to 10?2?mol?L?1. The electrodes show Nernstian slope value of 52.51 ± 0.20 and 51.51 ± 0.25?mV?decade?1 for CPE and PVC membrane electrodes at 30°C, respectively. The potential is nearly stable over the pH range 3.0–6.0 and 2.0–7.0 for CPE and PVC membrane electrodes, respectively. Selectivity coefficient values towards different inorganic cations, sugars, and amino acids reflect high selectivity of the prepared electrodes. The electrodes responses at different temperatures were also studied, and long operational lifetime of 12 and 5 weeks for CPE and PVC membrane electrodes, respectively, were found. These are used for determination of ketotifen fumarate using potentiometric titration, calibration, and standard addition methods in pure samples, its pharmaceutical preparations (Zaditen tablets), and biological fluid (urine). The direct potentiometric determination of KTF using the proposed sensors gave recoveries % of 98.97 ± 0.53 and 98.62 ± 0.74 with RSD 1.42 and 0.63% for CPE and PVC membrane selective electrodes, respectively. Validation of the method shows suitability of the proposed sensors for use in quality control assessment of KTF. The obtained results were in a good agreement with those obtained using the reported spectrophotometric method.

Frag, Eman Y. Z.; Mohamed, Gehad G.; Khalil, Mohamed M.; Hwehy, Mohammad M. A.

2011-01-01

88

Potentiometric propranolol-selective sensor based on molecularly imprinted polymer.  

PubMed

A novel potentiometric sensor based on molecularly imprinted polymer (MIP) for propranolol, an adrenergic-blocking drug, was designed. The influence of molecularly imprinted polymer particle content and sodium tetraphenylborate additives in polyvinylchloride membrane was shown. The electrodes show near-Nernstian responses down to 10(-4)-10(-5) M propranolol concentration. The potentiometric response of MIP-based sensor for propranolol in mixed nonaqueous medium was shown at first. Sensor selectivity relative to various inorganic cations, atenolol and metoprolol, was reported. Direct potentiometry was used to determine propranolol in aqueous modeling solutions and pharmaceutical preparations with good results. PMID:23104313

Gurtova, O; Ye, L; Chmilenko, F

2012-10-28

89

Permian potentiometric analysis  

Microsoft Academic Search

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

Devary

1983-01-01

90

Preparation and Potentiometric Determination of Quaternary N-Methiodides of Phenothiazine Derivatives  

Microsoft Academic Search

A method for the quantitative preparation of quaternary N-methiodides of phenothiazine derivatives has been developed. The products of the quaternization reaction were determined by potentiometric titration or by direct measurement of the potential of the indicator iodide ion-selective electrode.

H. Hopka?a

1990-01-01

91

An elevated temperature titration calorimeter  

NASA Astrophysics Data System (ADS)

A variable-temperature (313 K to 353 K) titration calorimeter of high sensitivity has been constructed. The purpose of the calorimeter is to study temperature effects on the enthalpies of complex formation and of other reactions of metal cations such as hydrolysis and precipitation. Operation of the calorimetric system, including that final calculation of the heat released during titration, is automatic via computer control. Calibration tests of the calorimeter using 2-amino 2-hydroxymethyl 1,3-propanediol gave -(46.0 +/- 0.3) kJ/mol and -(46.2 +/- 0.2) kJ/mol for the enthalpy of protonation, at 318 K and at 343 K, respectively. For titrations of 2-bis(2-hydroxyethyl) amino 2-hydroxymethyl 1,3-propanediol, enthalpy of protonation values of -(28.4 +/- 0.3) kJ/mol and -(29.3 +/- 0.2) kJ/mol were obtained at 318 K and at 343 K, respectively.

Smith, J. R.; Zanonato, P. L.; Choppin, G. R.

1991-06-01

92

An elevated temperature titration calorimeter  

SciTech Connect

A variable-temperature (313 K to 353 K) titration calorimeter of high sensitivity has been constructed. The purpose of the calorimeter is to study temperature effects on the enthalpies of complex formation and of other reactions of metal cations such as hydrolysis and precipitation. Operation of the calorimetric system, including that final calculation of the heat released during titration, is automatic via computer control. Calibration tests of the calorimeter using 2-amino-2-hydroxymethyl-1,3-propanediol gave -(46.0 {plus minus} 0.3) kJ mol{sup {minus}1} and -(46.2 {plus minus} 0.2) kJ mol{sup {minus}1} for the enthalpy of protonation, at 318 K and at 343 K, respectively. For titrations of 2-bis(2-hydroxyethyl) amino-2-hydroxymethyl-1,3-propanediol, enthalpy of protonation values of -(28.4 {plus minus} 0.3) kJ mol{sup {minus}1} and -(29.3 {plus minus} 0.2) kJ mol{sup {minus}1} were obtained at 318 K and at 343 K, respectively. 6 refs., 3 figs., 2 tabs.

Smith, J.R.; Zanonato, P.L.; Choppin, G.R. (Florida State Univ., Tallahassee, FL (USA). Dept. of Chemistry)

1991-06-01

93

Potentiometric determination of maleic anhydride in the presence of cis-3,6-endomethylene-1,2,3,6-tetrahydrophthalic (endic) anhydride  

Microsoft Academic Search

A procedure is developed for the determination of maleic anhydride in the presence of endic anhydride by potentiometric titration\\u000a in aqueous-organic solutions. It is found that separate titration of a hydrolyzed mixture of anhydrides is most efficient\\u000a in the system acetonitrile-water (3 : 2).

Yu. M. Evtushenko; B. E. Zaitsev; V. M. Ivanov

2000-01-01

94

Characterization of petroleum sulfonates by a nonaqueous titration method  

SciTech Connect

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 calculated from the grams of sample titrated and the moles of acid used. The potentiometric titration can be carried out in less than 10 minutes and can be done with 10 to 100 mg of sample. The accuracy and precision of the procedure were examined by the titration of sodium salts of p-toluene sulfonate, 2-naphthalene sulfonate, and petroleum sulfonates. In general, values for the equivalent weight were within 2% of those values determined by the Epton titration, by wet ashing methods, or from the theoretical value. The relative standard deviation (RSD) for the procedure is estimated to be 0.5%. For p-toluene sulfonate, an RSD of 0.15% was calculated. Petroleum sulfonates are used to liberate a residual oil from a porous medium in a tertiary oil-recovery process. 24 refs.

Voss, K.R.; Bricker, C.E.; Michnick, M.J.; Willhite, G.P.

1981-12-01

95

Coulometric Titration of Wustite.  

National Technical Information Service (NTIS)

The existence range and oxygen activity as functions of composition were determined for wustite from 765 to 965C by solid-electrolyte galvanic cell measurements. The composition changes were effected by coulometric titration. The results are in excellent ...

F. E. Rizzo J. V. Smith

1968-01-01

96

[A potentiometric method of quantitative analysis of rifampicin].  

PubMed

A potentiometric procedure for assay of rifampicin was developed. The procedure implies titration of rifampicin as a monofunctional acid by sodium hydroxide solution (0.1 mol/l) in 75 per cent aqueous methanol. The constant ionic strength of the solution is provided by addition of KCl until its concentration is 0.1 mol/l, the titrant concentration being 10 times higher than the antibiotic concentration in the solution. This provides a precise determination of the concentration ionization constant of the antibiotic as a monofunctional acid (pKa 7.33 +/- 0.01) and an insignificant dilution of the antibiotic solution during the titration promoting precise and reproducible results. The procedure error is 0.20 per cent. The variation coefficient is 0.27 per cent. PMID:2337377

Ovcharova, G D; Nacheva, R N; Dimitrova, D B

1990-02-01

97

Septonex-tetraphenylborate screen-printed ion selective electrode for the potentiometric determination of Septonex in pharmaceutical preparations.  

PubMed

A screen-printed electrode (SPE) was fabricated for the determination of 1-(ethoxycarbonyl)pentadecyltrimethylammonium bromide (Septonex) based on the use of Septonex-tetraphenylborate as the electroactive substance, and o-nitrophenyloctylether (o-NPOE) as the plasticizing agent. The electrode passes a near-Nernstian cationic slope of 59.33 ± 0.85 mV from activity between pH values of 2 to 9 with a lower detection limit of 9×10(-7) M and response time of about 5 s and exhibits an adequate shelf-life of 6 months. The method was applied for the determination of Septonex in pharmaceutical preparations. A percentage recovery of 99.88% was obtained with RSD=1.24%. The electrode was successfully applied in the determination of Septonex in laboratory-prepared samples by direct potentiometric, calibration curve and standard addition methods. Potentiometric titration of Septonex with sodium tetraphenylborate and phosphotungstic acid as a titrant was monitored with the modified screen-printed electrode as an end-point indicator electrode. Selectivity coefficients for Septonex relative to a number of potential interfering substances were determined. The sensor was highly selective for Septonex over a large number of compounds. Selectivity coefficient data for some common ions show negligible interference; however, cetyltrimethylammonium bromide and iodide ions interfere significantly. The analytical usefulness of the proposed electrode was evaluated by its application in the determination of Septonex in laboratory-prepared pharmaceutical samples with satisfactory results. The results obtained with the fabricated sensor are comparable with those obtained by the British Pharmacopeia method. PMID:21286616

Mohamed, Gehad G; El-Shahat, M F; Al-Sabagh, A M; Migahed, M A; Ali, Tamer Awad

2011-02-02

98

Potentiometric determination of the ‘formal’ hydrolysis ratio of aluminium species in aqueous solutions  

Microsoft Academic Search

The ‘formal’ hydrolysis ratio (h=C(OH?)added\\/C(Al)total) of hydrolysed aluminium-ions is an important parameter required for the exhaustive and quantitative speciation–fractionation of aluminium in aqueous solutions. This paper describes a potentiometric method for determination of the formal hydrolysis ratio based on an automated alkaline titration procedure. The method uses the point of precipitation of aluminium hydroxide as a reference (h=3.0) in order

Agathe C. Fournier; Kirill L. Shafran; Carole C. Perry

2008-01-01

99

Potentiometric measurement of stability constants of complexes between fulvic acid carboxylate and Fe 3+  

Microsoft Academic Search

The stability constants of complexes formed between iron (III) and fulvic acid extracted from organic manures and wastes such\\u000a as urban domestic sewage sludge, farmyard manure, poultry manure and sulfitation pressmud were investigated by the potentiometric\\u000a titration method in an ionic medium of 0.1 M KNO3 at 25±1 °C. A modification of the Katchalsky's model was employed for the estimation

S. B. Pandeya; A. K. Singh

2000-01-01

100

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

101

Theoretical problems associated with the use of acetic anhydride as a co-solvent for the non-aqueous titration of hydrohalides of organic bases and quaternary ammonium salts  

Microsoft Academic Search

A potentiometric titration study of organic base hydrohalides and quaternary ammonium salts using perchloric acid as the titrant and a mixture of acetic anhydride and acetic acid as the solvent was carried out and the titration mixture was analysed by NMR in order to clarify the chemistry of the reactions involved. It was found that in contrast to the general

Gergely Völgyi; Szabolcs Béni; Krisztina Takács-Novák; Sándor Görög

2010-01-01

102

Neutron absorptiometric titration.  

PubMed

A method is outlined for detection of two-phase titration end-points by means of an abrupt change in the neutron-absorption characteristics of one of the phases. One of the components of the precipitate must have a large neutron absorption cross-section, and the disappearance or appearance of neutron absorption by the supernatant liquid from the precipitation reaction then marks the completion of precipitation. PMID:18960115

Tölgyessy, J; Varga, S; Dillinger, P

1967-03-01

103

Titration Curves: Fact and Fiction.  

ERIC Educational Resources Information Center

|Discusses ways in which datalogging equipment can enable titration curves to be measured accurately and how computing power can be used to predict the shape of curves. Highlights include sources of error, use of spreadsheets to generate titration curves, titration of a weak acid with a strong alkali, dibasic acids, weak acid and weak base, and…

Chamberlain, John

1997-01-01

104

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

105

Development of a potentiometric flow cell with a stainless steel electrode for pH measurements. Determination of acid mixtures using flow injection analysis  

Microsoft Academic Search

In this work a stainless steel electrode was prepared, characterised and used as indicator electrode in a potentiometric flow cell. Due to its versatility, it was possible to study different electrode geometries and flow cell arrangements. After optimising the system, mixtures of succinic and oxalic acids were determined by titration. Partial least squares (PLS) regression as multivariate calibration tool was

Cleidiane G Zampronio; Jarbas J. R Rohwedder; Ronei J Poppi

2000-01-01

106

Radiometric acid-base titrations.  

PubMed

Acid-base titrations can be performed with radiometric end-point detection by use of labelled metal salts (e.g., ZnCl(2), HgCl(2)). Owing to the formation or dissolution of the corresponding hydroxide after the equivalence point, the activity of the titrated solution linearly increases or decreases as excess of standard solution is added. The end-point of the titration is determined graphically. PMID:18960522

Erdey, L; Gimesi, O; Szabadváry, F

1969-03-01

107

Studies on the potentiometric thallium(III)-selective carbon paste electrode and its possible applications  

Microsoft Academic Search

Construction, performance characteristics and applications of a carbon paste thallium(III) ion-selective electrode are described.\\u000a The electrode, which is based on ion-associate compounds formed between cetylpyridinium and chlorothallate(III) complexes\\u000a dissolved in tricresyl phosphate as pasting liquid, showed near-Nernstian response over the concentration range of 5.8 × 10–6– 2.9 × 10–3 mol\\/L. Potentiometric titrations of thallium(III) with cetylpyridinium chloride were affected by

K. Vyt?as; E. Khaled; J. Ježková; H. N. A. Hassan; B. N. Barsoum

2000-01-01

108

Amperometric, Bipotentiometric, and Coulometric Titration.  

ERIC Educational Resources Information Center

Discusses recent review articles in various kinds of titration. Also discusses new research in apparatus and methodology, acid-base reactions, precipitation and complexing reactions, oxidation-reduction reactions, and nomenclature. Cites 338 references. (CS)

Stock, John T.

1980-01-01

109

Amperometric, Bipotentiometric, and Coulometric Titration.  

ERIC Educational Resources Information Center

|Discusses recent review articles in various kinds of titration. Also discusses new research in apparatus and methodology, acid-base reactions, precipitation and complexing reactions, oxidation-reduction reactions, and nomenclature. Cites 338 references. (CS)|

Stock, John T.

1980-01-01

110

PRINCIPAL AQUIFERS, CURRENT POTENTIOMETRIC SURFACE MAPS, NC  

EPA Science Inventory

Web page from North Carolina Department of Environment and Natural Resources (NC-DENR) to maps of potentiometric surfaces by aquifer in NC. http://www.dwr.ehnr.state.nc.us/hms/gwbranch/charact.htm ...

111

Novel sensors for potassium, calcium and magnesium ions based on a silicon transducer as a light-addressable potentiometric sensor  

Microsoft Academic Search

Potentiometric cation sensors using a silicon transducer, light-addressable potentiometric sensor (LAPS) and ion-recognition elements are described, and their performance are discussed. In the silicon transducer, an Al2O3 layer was used as an insulating layer. On the surface of the Al2O3 layer, ion-recognition element such as valinomycin, 18-crown-6 ether, bis[di(n-octylphenyl)phosphato]calcium(II) and ETH1117 were immobilized in the matrix of poly(vinyl chloride) film.

Atsushi Seki; Kentaro Motoya; Sinya Watanabe; Izumi Kubo

1999-01-01

112

Response mechanism of potentiometric Ag + sensor based on poly(3,4-ethylenedioxythiophene) doped with silver hexabromocarborane  

Microsoft Academic Search

Potentiometric Ag+ sensors were prepared by galvanostatic electropolymerization of 3,4-ethylenedioxythiophene (EDOT) on glassy carbon electrodes by using silver 7,8,9,10,11,12-hexabromocarborane (Ag+CB11H6Br6-) as supporting electrolyte. The analytical performance of the resulting GC\\/PEDOT(CB11H6Br6-) sensors was studied by potentiometric measurements. The electrodes showed a selective response to Ag+ compared to several alkali, alkaline-earth, and transition-metal cations. Pretreatment of the electrodes by cyclic voltammetry was

Zekra Mousavi; Johan Bobacka; Andrzej Lewenstam; Ari Ivaska

2006-01-01

113

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

114

Quantitative analysis of dimethyl titanocene by iodometric titration, gas chromatography and NMR.  

PubMed

In this study we report the use of an automated iodometric titration method and a novel gas chromatography (GC) method for the quantitative analysis of dimethyl titanocene (DMT), a key raw material in drug synthesis. Both approaches are based on the reaction of DMT in toluene or tetrahydrofuran solutions with iodine. In the case of iodometric titration, excess iodine is titrated with a standardized aqueous sodium thiosulfate solution to a potentiometric end-point for the determination of DMT concentration. Alternatively, GC is employed to measure the concentration of iodomethane, a product of the reaction between DMT and iodine, in order to determine the concentration of DMT in the solution. Excellent agreement between iodometric titration, GC and NMR results using several DMT samples confirms the accuracy of the two methods and strongly supports the use of either method as a replacement to the expensive NMR for quantitative DMT analysis. The relatively few sources of error associated with the two methods, their ubiquitous nature and ease of application in routine analysis make them the analytical methods of choice, among all. Both methods have been validated according to ICH requirements. The use of iodometric titration method for DMT analysis is demonstrated with a couple of applications. PMID:11377038

Vailaya, A; Wang, T; Chen, Y; Huffman, M

2001-06-01

115

The potentiometric determination of stability constants for zinc acetate complexes in aqueous solutions to 295C  

SciTech Connect

A potentiometric method was used to determine the formation quotients of zinc acetate complexes in aqueous solutions from 50 to 295C at ionic strengths of 0.03, 0.3, and 1.0 m. The potentiometric titrations were carried out in an externally heated, Teflon-lined concentration cell fitted with hydrogen electrodes. Formal sodium acetate concentrations of the experimental solutions ranged from 0.001 to 0.1 m with acetic acid to sodium acetate ratios ranging from 30 to 300. Sodium trifluoromethanesulfonate (F{sub 3}CSO{sub 3}Na) was used as a supporting electrolyte. Stoichiometries and formation quotients for the complexes ZnCH{sub 3}COO{sup +}, Zn(CH{sub 3}COO){sub 2}, and Zn(CH{sub 3}COO){sub 3}{sup {minus}} were derived from the titration data by regression analysis. Stability constants at infinite dilution (K{sub n}) and other relevant thermodynamic quantities were calculated for these three complexes. Calculations of zinc speciation in acetate-chloride solutions show that zinc acetate complexes should have an importance similar to zinc chloride complexes in high acetate waters where chloride to acetate molal ratios are less than about 10.

Giordano, T.H. (New Mexico State Univ., Las Cruces (United States)); Drummond, S.E. (Oak Ridge National Lab., TN (United States))

1991-09-01

116

Simple PVC-PPy electrode for pH measurement and titrations  

Microsoft Academic Search

Cobaltabis(dicarbollide) [3,3'-Co(1,2-C2B9H11)]--doped polypyrrole (PPy) films have been prepared galvanostatically on glassy carbon electrodes in acetonitrile solution. The potential response behavior of the film of this new material has been investigated in some common pH buffers and in acid-base titrations. The potentiometric characteristics of the resulting films are indicative of a quasi-Nernstian response (approximately 50 mV\\/pH unit), a linearity range from

C. Masalles; S. Borrós; C. Viñas; F. Teixidor

2002-01-01

117

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

118

Solution interactions between the uranyl cation [UO2(2+)] and histidine, N-acetyl-histidine, tyrosine, and N-acetyl-tyrosine.  

PubMed

Complexes of the uranyl cation [UO(2)(2+)] with histidine (His), N-acetyl-histidine (NAH), tyrosine (Tyr), and N-acetyl-tyrosine (NAT) were studied by UV-visible and NMR spectroscopy, and by potentiometric titration. Protonation constants for each ligand are reported, as are cumulative formation constants for uranyl-amino acid complexes. Coupling constant data (J(CH)) for uranyl-histidine complexes indicate that inner-sphere solution interactions between histidine and uranyl cation are solely at the carboxylate site. At 25 degrees C the major uranyl-histidine complex has a cumulative formation constant of logbeta(110)=8.53, and a proposed formula of [UO(2)HisH(2)(OH)(2)](+); the stepwise formation constant, logK(UL), is estimated to be 5.6 ( approximately 8.53-(-6.1)-(-6.1)-15.15). Outer-sphere interactions, H-bonding or electrostatic interactions, are proposed as contributing a significant portion of the stability to the ternary uranyl-hydroxo-amino acid complexes. The temperature dependent protonation constants of histidine and formation constants between uranyl cation and histidine are reported from 10 to 35 degrees C; at 25 degrees C, DeltaG=-43.3 kJ/mol. PMID:18947879

Xie, Wei; Badawi, Ahmed; Huang, Huan; Van Horn, J David

2008-09-19

119

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

120

A pH and Redox-Potentiometric Study of Equilibria between Fe(II), Fe(III), and N-(Carboxymethyl)Aspartic Acid  

Microsoft Academic Search

Complexation in the Fe2+–Fe3+–N-(carboxymethyl)aspartic acid (H3L) system in aqueous solutions was studied by pH- and redox-potentiometric titration at 25°C and at an ionic strength of 0.1 (KCl). Depending on the H3L concentration and pH, neutral, protonated, and hydroxo complexes of iron(III) can be formed in the solutions. The stability constants for all the detected complexes were calculated, and the distribution

N. E. Knyazeva; V. M. Nikol'skii; I. P. Gorelov

2002-01-01

121

Surface complexation of neodymium at the rutile-water interface: A potentiometric and modeling study in NaCl media to 250°C  

Microsoft Academic Search

The adsorption of Nd3+ 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 Nd3+ sorbs strongly, even at low temperature, with adsorption commencing below the pHznpc of rutile. In addition, there is a systematic increase in Nd3+ adsorption with increasing temperature. The experimental results were rationalized

Moira K. Ridley; Michael L. Machesky; David J. Wesolowski; Donald A. Palmer

2005-01-01

122

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

123

Cyclodextrin-based dextromethorphan potentiometric sensors  

Microsoft Academic Search

The construction and performance characteristics of different dextromethorphan (DXM) potentiometric sensors are described. Three types of electrodes are demonstrated, namely silver coated wire electrode (CWE), coated graphite electrode (CGE) and the conventional PVC membrane electrodes (CE). The cited electrodes are based on cyclodextrins (CDs) ionophores and show a considerable selectivity towards DXM with Nernstian slopes depending on the type of

Elmorsy Khaled; Manal S. Kamel; Hassan N. A. Hassan; Hassan Y. Aboul-Enein

2011-01-01

124

Simple Potentiometric Determination of Reducing Sugars  

ERIC Educational Resources Information Center

|In this article a potentiometric method for reducing sugar quantification is described. Copper(II) ion reacts with the reducing sugar (glucose, fructose, and others), and the excess is quantified using a copper wire indicator electrode. In order to accelerate the kinetics of the reaction, working conditions such as pH and temperature must be…

Moresco, Henry; Sanson, Pedro; Seoane, Gustavo

2008-01-01

125

Automatic titrator for high precision plutonium assay  

SciTech Connect

Highly precise assay of plutonium metal is required for accountability measurements. We have developed an automatic titrator for this determination which eliminates analyst bias and requires much less analyst time. The analyst is only required to enter sample data and start the titration. The automated instrument titrates the sample, locates the end point, and outputs the results as a paper tape printout. Precision of the titration is less than 0.03% relative standard deviation for a single determination at the 250-mg plutonium level. The titration time is less than 5 min.

Jackson, D.D.; Hollen, R.M.

1986-01-01

126

Fluorapatite surface composition in aqueous solution deduced from potentiometric, electrokinetic, and solubility measurements, and spectroscopic observations  

NASA Astrophysics Data System (ADS)

The surface chemistry of fluorapatite in aqueous solution was investigated using electrokinetic techniques, potentiometric titrations, solubility measurements, and attenuated total reflection infrared spectroscopy. All methods indicate the formation of Ca/F depleted, P enriched altered layer via exchange reactions between H + and Ca 2+, and OH - and F - at the fluorapatite (FAP) surface. Observations suggest that this leached layer has a di-calcium phosphate (CaHPO 4) composition and that it controls the apparent solubility of FAP. Electrokinetic measurements yield an iso-electric point value of 1 ± 0.5 consistent with a negatively charged FAP surface at pH > 1. In contrast, surface titrations give an apparent pH of point of zero charge of ˜7.7, consistent with a positively charged surface at pH < 7.7. These differences are shown to stem from proton consumption by both proton exchange and dissolution reactions at the FAP surface. After taking account for these effects, FAP surface charge is shown to be negative to at least pH 4 by surface titration analysis.

Chaïrat, Claire; Oelkers, Eric H.; Schott, Jacques; Lartigue, Jean-Eric

2007-12-01

127

Solid titration of octacalcium phosphate.  

PubMed

Octacalcium phosphate (OCP) is of considerable importance as a precursor in the formation of dental enamel and an intermediate phase in the precipitation of hydroxyapatite (HAp) in bone. However, agreement is poor on the solubility product (pK(sp)), possibly due to the formation of the more stable phase HAp. The system was investigated using solid titration, which has shown reliability in work on HAp and related fluoride minerals, with OCP in 100 mM KCl at 37.0 +/- 0.1 degrees C. The constitution of the end point precipitate was determined by X-ray diffraction and selected-electron area diffraction; the particle morphology and elements present were examined by high-resolution field emission scanning, transmission electron microscopy and energy-dispersive X-ray analysis. The titration curve for OCP was found for pH approximately 3.4-7.4. The precipitate was HAp at pH 3.6 and 4.5; no residual OCP or other phase was detected. Dicalcium phosphate dihydrate (DCPD) was then found to form at pH 3.6 on further addition of OCP titrant after equilibrium had been achieved, possibly due to easier nucleation at lower pH. However, markedly crystalline HAp was formed in equilibrium for OCP titration with HAp seeding, verifying HAp as the more stable phase. A solubility isotherm for OCP was not obtained as HAp appears to be less soluble in the pH range studied. This adds weight to the view that HAp may be the most stable phase of all calcium phosphates, with further doubt being cast on DCPD being the most stable phase below pH 4.2. However, metastable DCPD may form in an Ostwald succession, depending on supersaturation and nucleation conditions. PMID:19556792

Pan, H-B; Darvell, B W

2009-06-24

128

Acid-Base Equilibria and Titrations and Electrochemical Equilibria in Acetonitrile.  

National Technical Information Service (NTIS)

Very briefly discussed are studies which have been made of acid-base equilibria and titrations and also of conjugation in acetonitrile (AN) as a solvent. Dissociation constants of a host of uncharged and cationic acids have been determined, including acid...

I. M. Koltoff

1971-01-01

129

Disposable potentiometric sensors for monitoring cholinesterase activity  

Microsoft Academic Search

A highly sensitive disposable screen-printed butyrylcholine (BuCh) potentiometric sensor, based on heptakis (2,3,6-tri-o-methyl)-?-cyclodextrin (?-CD) as ionophore, was developed for butyrylcholinesterase (BuChE) activity monitoring. The proposed sensors have been characterized and optimized according to the constituents of homemade printing carbon ink including ?-CD, anionic sites, and plasticizer. The fabricated sensor showed Nernstian responses from 10?6 to 10?2molL?1 with detection limit of

Elmorsy Khaled; H. N. A. Hassan; Gehad G. Mohamed; Fahem A. Ragab; Aly Eldin A. Seleim

2010-01-01

130

Potentiometric biosensors based on polyaniline semiconductor films  

Microsoft Academic Search

Application of polyaniline (PAn) semiconductor films for potentiometric biosensor development provides certain advantages compared with the known systems. For enzyme immobilisation a pH sensitive matrix was used, which could improve sensor sensitivity. Indeed the limiting response value of the PAn based trypsin electrode in 1 mM buffer was 270 mV. The maximal slope of the calibration curve in semilogarithmic coordinates

Arkady A. Karyakin; Oksana A. Bobrova; Lylia V. Lukachova; Elena E. Karyakina

1996-01-01

131

Modeling of light-addressable potentiometric sensors  

Microsoft Academic Search

In this paper, the extension of numerical simulation techniques to the analysis of light-addressable potentiometric sensors (LAPS) is discussed in detail. To this purpose, proper physical models of both the ion-sensitive and the photo-sensitive transduction mechanisms have been incorporated into the framework of a general-purpose device simulator. A self-consistent, accurate picture of charge transport within the device under the combined

Luigi Colalongo; Giovanni Verzellesi; Daniele Passeri; A. Lui; Paolo Ciampolini; Massimo V. Rudan

1997-01-01

132

Protonation and Complexation of Isosaccharinic Acid with U(VI) and Fe(III) in Acidic Solutions: Potentiometric and Calorimetric Studies  

SciTech Connect

Protonation and complexation of {alpha}-isosaccharinic acid with U(VI) and Fe(III) have been studied in acidic solutions at t=25 C and I=1.0 mol dm{sup -3} NaClO{sub 4}. From the potentiometric titrations, the protonation constant of the carboxylate group is calculated to be 3.65 {+-} 0.05 and the data are consistent with the presence of three and four successive mononuclear complexes for U(VI) and Fe(III), respectively. The formation constants of the complexes, log {beta}{sub j}for the reactions of M+L=ML{sub j} where j=1-3 for U(VI), j=1-4 for Fe(III) and L stands for isosaccharinate, are determined to be 2.91 {+-} 0.15 (UO{sub 2}L), 5.37 {+-} 0.07 (UO{sub 2}L{sub 2}), 7.25 {+-} 0.18 (UO{sub 2}L{sub 3}), 5.06 {+-} 0.17 (FeL), 8.51 {+-} 0.15 (FeL{sub 2}), 11.00 {+-} 0.16 (FeL{sub 3}), and 12.99 {+-} 0.17 (FeL{sub 4}). From the calorimetric titrations, the enthalpy of protonation of the carboxylate group is determined to be -(7.94 {+-} 0.03)kJ mol{sup -1}, similar to that of other ?-hydroxycarboxylates. The enthalpies of complexation between U(VI) and isosaccharinate are quite small: {Delta} H{sub 1} = -(1.0 {+-} 1.0)kJ mol{sup -1}, {Delta} H{sub 2}=1.4 {+-} 1.8 kJ mol{sup -1} and {Delta} H{sub 3}=-(6.2 {+-} 3.0)kJ mol{sup -1}, typical of the interactions between carboxylates and hard-acid cations. The complexation between U(VI) and isosaccharinate is mainly entropy-driven. In comparison, the enthalpies of complexation for FeL{sub 3} and FeL{sub 4} are large and exothermic, contributing significantly to the stability of the complexes.

Rao, Linfeng; Garnov, A Y.; Rai, Dhanpat; Xia, Yuanxian; Moore, R C.

2004-12-01

133

Lead-selective membrane potentiometric sensor based on a recently synthesized bis(anthraquinone) sulfide derivative  

SciTech Connect

The need for monitoring of toxic heavy metal ions in environmental samples has prompted the development of ion-selective electrodes for these ions. A new PVC membrane electrode for lead ions, based on bis[(1-hydroxy-9,10-anthraquinone)-2-methyl]sulfide as membrane carrier, was prepared. The sensor exhibits a Nernstian response for Pb{sup 2+} over a wide concentration range (5.6 {times} 10{sup {minus}3}--4.0 {times} 10{sup {minus}6} M). It has a response time of about 30 s and can be used for at least 3 months without any divergence in potentials. The proposed membrane sensor revealed good selectivities for Pb{sup 2+} over a wide variety of other metal ions. It was used as an indicator electrode in potentiometric titration of lead ion.

Pouretedal, H.R.; Forghaniha, A.; Sharghi, H. [Shiraz Univ. (Iran, Islamic Republic of). Dept. of Chemistry; Shamsipur, M. [Razi Univ., Kermanshah (Iran, Islamic Republic of). Dept. of Chemistry

1998-12-01

134

Sorption and desorption of quaternary amine cations on clays  

Microsoft Academic Search

The authors have studied the sorption and desorption of three quaternary amines, namely, nonyltrimethylammonium, dodecyltrimethylammonium, and hexadecyltrimethylammonium, on homoionic Na- and K-montmorillonite using a titration procedure. More than 99% of all three of the quaternary amine cations studied were sorbed on the montmorillonite when the added amines were less than 70% of the cation-exchange capacity of the montmorillonite. Sorption of

Z. Zhong Zhang; Donald L. Sparks; Noel C. Scrivner

1993-01-01

135

Determination of Solanesol by Coulometric Titration  

Microsoft Academic Search

A method for determination of solanesol by coulometric titration was developed. The titration was carried out in a mixture of 2M KBr-glacial acetic acid (22:78 v\\/v), and bromine was generated at the anode. Solanesol reacted with bromine with a value of n = 18. The end point of the titration was detected with two-electrode amperometry. The method is rapid, accurate

Kuai Zhi Liu; Meng Liu; Deliang Li

1998-01-01

136

Spectrophotometric, potentiometric, and gravimetric determination of lanthanides with peri-dihydroxynaphthindenone  

SciTech Connect

Sensitive and reasonably selective methods are described for the spectrophotometric, potentiometric, and gravimetric determination of lanthanides using peri-dihydroxynaphthindenone as a novel chromogenic and precipitating reagent. The reagent forms a stable 1:2 (metal:reagent) type of complex with light lanthanides at pH 2-7 in 1:1 ethanol-water mixture. Low metal concentrations (<10 ..mu..g/mL) develop colored species (lambda/sub max/ 580 to 590 nm, epsilon/sub max/ (4-6) x 10/sup 4/ L mol/sup -1/ cm/sup -1/) which obey Beer's law. Quantitative precipitation of the complexes from metal solutions of concentrations > 100 ..mu..g/mL permits both gravimetric quantitation by igniting the precipitates to the metal oxides and potentiometric titration of the excess reagent. Results with an average recovery of 98% (standard deviation 0.7%) are obtainable for 0.1 ..mu..g to 200 mg of all light lanthanides. Many foreign ions naturally occurring or frequently associated with lanthanides do not interfere or can be tolerated.

Hassan, S.S.M.; Mahmoud, W.H.

1982-02-01

137

Isothermal Titration Calorimetry of RNA  

PubMed Central

Isothermal titration calorimetry (ITC) is a fast and robust method to study the physical basis of molecular interactions. A single well-designed experiment can provide complete thermodynamic characterization of a binding reaction, including Ka, ?G, ?H, ?S and reaction stoichiometry (n). Repeating the experiment at different temperatures allows determination of the heat capacity change (?CP) of the interaction. Modern calorimeters are sensitive enough to probe even weak biological interactions making ITC a very popular method among biochemists. Although ITC has been applied to protein studies for many years, it is becoming widely applicable in RNA biochemistry as well, especially in studies which involve RNA folding and RNA-interactions with small molecules, proteins and with other RNAs. This review focuses on best practices for planning, designing, and executing effective ITC experiments when one or more of the reactants is an RNA.

Salim, Nilshad N.; Feig, Andrew L.

2009-01-01

138

On the water dispersibility of a 1:1 stoichiometric complex between a cationic nanogel and linear polyanion.  

PubMed

This work aimed to obtain information on the water dispersibility of a 1:1 stoichiometric polyelectrolyte nanogel complex (SPENC). We synthesized a cationic polyelectrolyte nanogel (CPENG) composed of a cross-linked copolymer of 1-vinylimidazole and N-isopropylacrylamide. SPENC was then prepared at 25 degrees C from the mixing of equimolar amounts (based on fixed charges) of CPENG and potassium poly(vinyl alcohol) sulfate, which were dissolved in an aqueous solution without adding salt and at pH 3.0. We carefully observed at 25 degrees C the reduction of the imidazole-based cationic charge in the CPENG component of SPENC as a function of pH. Dynamic and static light scattering techniques were employed in combination with electrophoretic light scattering experiments. The amount of cationic charge in the SPENC was estimated from the potentiometric titration data of CPENG. It was found that, during the charge reduction process, the complex underwent aggregation, followed by a phase separation. The aggregation started at about 25% of the charge reduction (i.e., at pH approximately = 4.9), and the phase separation took place when almost half of the charge was eliminated (at pH approximately = 5.5). However, the phase-separated complexes became water-soluble again when about 90% of the charge was eliminated (pH approximately = 6.6). By colloid titration, the dissociated free polyanions were not detected in the aqueous SPENC solution before the phase separation but were detected in the complex-redispersed solution. When the pH (9.0) of the redispersion was slowly decreased to the original level (pH 3.0) by the gradual addition of HCl so as to cause again the phase separation, an intraparticle complex was reformed, the physical quantities of which were close to those of the initial SPENC. These findings clearly indicate that the whole and a part (segment) of the complexed polyanions undergoes dissociation-association reactions on the surface of a SPENC particle, depending on the ionization state of the cationic gel component. As a result, these reactions seem to be a key factor for the water dispersibility of the SPENC. PMID:20695607

Doi, Ryo; Kokufuta, Etsuo

2010-08-17

139

Simple PVC-PPy electrode for pH measurement and titrations.  

PubMed

Cobaltabis(dicarbollide) [3,3'-Co(1,2-C2B9H11)](-)-doped polypyrrole (PPy) films have been prepared galvanostatically on glassy carbon electrodes in acetonitrile solution. The potential response behavior of the film of this new material has been investigated in some common pH buffers and in acid-base titrations. The potentiometric characteristics of the resulting films are indicative of a quasi-Nernstian response (approximately 50 mV/pH unit), a linearity range from pH 12 to 3 and correlation coefficients (r2) of approximately 0.98. The electrode is suitable for pH measurements and for monoprotic titrations of strong alkalis with strong acids, and weak bases with strong acids, but the long response time hinders the use of this electrode for multiprotic titrations. The time response has been dramatically improved by reducing the film thickness by using the template effect of a non-conducting polymer (PVC) cast over the graphite surface before PPy deposition. PPy polymerization occurs in the free channels of PVC leading to the formation of PPy wires. The morphological change of PPy does not affect the slope or linearity range. The response of the PVC-PPy electrochemical sensor is rapid and the sensor is easy to prepare, at low cost, and its performance is comparable with that of commercial glass electrodes. PMID:11939624

Masalles, C; Borrós, S; Viñas, C; Teixidor, F

2002-01-11

140

Spectroscopic study on variations in illite surface properties after acid-base titration.  

PubMed

FT-IR, Raman microscopy, XRD, 29Si and 27Al MAS NMR, were used to investigate changes in surface properties of a natural illite sample after acid-base potentiometric titration. The characteristic XRD lines indicated the presence of surface Al-Si complexes, preferable to Al(OH)3 precipitates. In the microscopic Raman spectra, the vibration peaks of Si-O and Al-O bonds diminished as a result of treatment with acid, then increased after hydroxide back titration. The varied ratio of signal intensity between (IV)Al and (VI)Al species in 27Al MAS NMR spectra, together with the stable BET surface area after acidimetric titration, suggested that edge faces and basal planes in the layer structure of illite participated in dissolution of structural components. The combined spectroscopic evidence demonstrated that the reactions between illite surfaces and acid-leaching silicic acid and aluminum ions should be considered in the model description of surface acid-base properties of the aqueous illite. PMID:12974304

Liu, Wen-xin; Coveney, R M; Tang, Hong-xiao

2003-07-01

141

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

142

Electronic tongue based on an array of metallic potentiometric sensors  

Microsoft Academic Search

An electronic tongue system based on the array of six metallic potentiometric sensors (metallic wires) was developed and utilized for discrimination of foodstuffs: several types of vinegar and fruit juices. Copper, tin, iron, aluminum, brass and stainless steel wires were included in the array and supplemented by pH glass electrode. The response of potentiometric metallic sensors towards various organic acids

Larisa Lvova; Eugenio Martinelli; Emiliano Mazzone; Andrea Pede; Roberto Paolesse; Corrado Di Natale; Arnaldo D’Amico

2006-01-01

143

Application of chemiluminescent indicators in EDTA titrations.  

PubMed

The chemiluminescent indicators lucigenine and luminol are readily applicable to end-point detection in the EDTA titration of cadmium, zinc and nickel ions. Back-titration with copper(II) gives reproducible results. The end-point is indicated by the disappearance of the green chemiluminescence of lucigenine, or by the appearance of the bluish luminescence of luminol. PMID:18960856

Erdey, L; Weber, O; Buzás, I

1970-12-01

144

CONSTANT CURRENT SOURCE FOR AUTOMATIC COULOMETRIC TITRATIONS  

Microsoft Academic Search

A simple but versatile constant current source for automatic coulometric ; titrations is described. The unit is suitable for use with a commercial ; automatic pH titrimeter and will accommodate wide variations of main voltage and ; load resistance. Coulometric titrations may be carried out fast'' or slow'' ; with a choice of four current ranges (2 to 37 ma)

A. R. Palmer; A. W. Pryor

1958-01-01

145

Light-addressable potentiometric fluoride (F ?) sensor  

Microsoft Academic Search

In this work, light-addressable potentiometric sensor (LAPS) has been investigated for fluoride (F?) sensing in aqueous medium. Vacuum-evaporated LaF3 has been studied as the fluoride-sensing layer in the LAPS heterostructure. Instead of using the conventional structure of Si\\/SiO2\\/LaF3 or Si\\/SiO2\\/Si3N4\\/LaF3, a simple structure of Si\\/LaF3 has been prepared as the LAP fluoride-sensor. The sensor was prepared with 50nm LaF3 layer

Koji Furuichi; Tatsuo Yoshinobu; Hiroshi Iwasaki

2002-01-01

146

[Potentiometric detection of beta-adrenolytic and beta-adrenergic drugs in HPLC systems].  

PubMed

This paper presents a comprehensive review of reference literature and the principal results of our own studies on the use of inclusion effects of macrocyclic compounds in the potentiometric detection of hypotensive and antiarrhythmic drugs as well as bronchodilators following their separation in HPLC systems. It was found that the properties of the liquid membrane electrodes embodying some macrocyclic compounds (i.e. trioctylated alpha-cyclodextrin, dibenzo-18-crown-6 or calix[6]arene hexaethylester) enabled reasonable prediction of their sensitivity in terms of the computed hydrophobicity and polarizability parameters of the analyzed drugs. The statistically significant equations enabling the optimalization of the composition of liquid membrane electrodes and the prediction of their detection limits in relation to the molecular structures of cationic drugs were established by applying multiparameter regression procedures. In particular it was indicated that the use of a liquid membrane electrode with trioctylated alpha-cyclodextrin enables sensitive detection (<10(-8) M) of highly hydrophobic drugs (logP >2.5 on the Parham-Hall-Kier scale) such as clenbuterol, bufuralol, and propanolol under HPLC conditions. These results indicate that the developed potentiometric detection method of hypotensive drugs can be considered as a promising alternative to the immunoassay procedures (ELISA) currently recommended for the toxicological determination of trace amounts of the drugs in biological samples. It was also shown that the set of experimentally determined detection limits characterizing the sensitivity of the four different liquid membrane electrodes used in the cation-exchange HPLC system enabled reliable screening and proper pharmacological classification of the beta-adrenergic and beta-adrenolytic drugs analyzed. Using principal component analysis (PCA) of the potentiometric data, it was stated that a differentiation of cardioselective from non-cardioselective beta1-blockers commonly administered as the hypotensive drugs was possible. This result indicates that the new method of potentiometric detection in HPLC systems can be applied as an effective high-throughput screening (HTS) procedure of large combinatorial libraries of newly synthesized drug-like candidates. This may increase the possibilities of identifying the lead compounds to be directed to further specialized biological tests, thus enabling the successful design and formulation of a new generation of more selective and pharmacogenome-oriented hypotensive drugs with reduced side-effects. PMID:16407794

Bazylak, Grzegorz; Nagels, Luc J

2005-01-01

147

A simple-potentiometric method for determination of acid and alkaline phosphatase enzymes in biological fluids and dairy products using a nitrophenylphosphate plastic membrane sensor  

Microsoft Academic Search

A novel poly(vinyl chloride) matrix membrane sensor responsive to 4-nitrophenylphosphate (4-NPP) substrate is described, characterized and used for the potentiometric assay of acid (ACP) and alkaline (ALP) phosphatase enzymes. The sensor is based on the use of the ion-association complex of 4-NPP anion with nickel(II)-bathophenanthroline cation as an electroactive material and nitrophenyloctyl ether (NPOE) as a solvent mediator. The sensor

Saad S. M. Hassan; Hossam E. M. Sayour; Ayman H. Kamel

2009-01-01

148

Effect of Cell Geometry in Coulometric Titrations.  

National Technical Information Service (NTIS)

In coulometric titrations the current flowing between the generator electrodes interferes with the operation of the indicator electrodes. In the case of parallel rod-shaped electrodes the error-signal curve that describes the extent of the interference ha...

D. Tamas

1974-01-01

149

Simultaneous use of evolving factor analysis of fluorescence spectral data and analysis of pH titration data for comparison of the acid-base properties of fulvic acids  

Microsoft Academic Search

Three fulvic acids (fua) extracted from a Portuguese pinewood soil (dry pine needles, fual, leaf litter, fua2, and lower soil horizon, fua3) have been studied by synchronous molecular fluorescence spectroscopy (SyF) at variable pH and by potentiometric pH titrations. The number of macroscopic acid-base systems and their pKas were calculated by analysis of the SyF-pH hyphenated data with a self-modeling

C. G. Joaquim; Esteves da Silva; Adélio A. S. C. Machado; Carla S. P. C. O. Silva

1996-01-01

150

Equilibrium studies of aspartame and some of its degradation products with hydrogen(I) and copper(II) under physiological conditions using potentiometric pH measurements  

Microsoft Academic Search

Equilibrium studies of N-L-?-aspartyl-L-phenylalanine 1-methyl ester (aspartame) and some of its degradation products (L-phenylalanine, L-aspartic acid) with hydrogen(I) and copper(II) were carried out under physiological conditions (I=0.15 M (NaCl) in water, 37°C) using potentiometric titrations. The concentration stability constants of binary and ternary complexes of copper(II) with aspartame, L-phenylalanine and L-aspartic acid, as well as those of the binary complexes

Sherif Kholeif; Giorgio Anderegg

1997-01-01

151

Study of inclusion complexes of cycloamylose with surfactants by isothermal titration calorimetry  

Microsoft Academic Search

Useful materials can be made from cycloamylose (CA) and the functional properties of CA could be improved by complexation with surfactants. Isothermal titration calorimetry (ITC) was used to investigate interactions between CA and surfactants in buffered solutions. Three surfactants with C12 non-polar tail groups and charged [anionic: sodium dodecyl sulfate (SDS); cationic: dodecyl trimethylammonium bromide (DTAB)] or non-charged headgroups [non-ionic:

Saehun Mun; Shin-Joung Rho; Yong-Ro Kim

2009-01-01

152

Potentiometric chemical sensors from lignin-poly(propylene oxide) copolymers doped by carbon nanotubes.  

PubMed

Hardwood and softwood lignins obtained from industrial sulphite and kraft and laboratory oxygen-organosolv pulping processes were employed in co-polymerization with tolylene 2,4-diisocyanate terminated poly(propylene glycol). The obtained lignin-based polyurethanes were doped with 0.72 w/w% of multiwall carbon nanotubes (MWCNTs) with the aim of increasing their electrical conductivity to the levels suitable for sensor applications. Effects of the polymer doping with MWCNTs were assessed using electrical impedance (EIS) and UV-Resonance Raman (UV-RR) spectroscopy. Potentiometric sensors were prepared by drop casting of liquid polymer on the surface of carbon glass or platinum electrodes. Lignin-based sensors displayed a very low or no sensitivity to all alkali, alkali-earth and transition metal cations ions except Cr(VI) at pH 2. Response to Cr(VI) values of 39, 50 and 53 mV pX(-1) for the sensors based on kraft, organosolv and lignosulphonate lignins, respectively, were observed. Redox sensitivity values close to the theoretical values of 20 and 21 mV pX(-1) for organosolv and lignosulphonate based sensors respectively were detected in the Cr(III)/Cr(VI) solutions while a very low response was observed in the solutions containing Fe(CN)(6)(3-/4-). Conducting composite lignin-based polyurethanes doped with MWCNTs were suggested as being promising materials for Cr(VI)-sensitive potentiometric sensors. PMID:23162814

Rudnitskaya, Alisa; Evtuguin, Dmitry V; Costa, Luis C; Graça, M Pedro F; Fernandes, António J S; Correia, M Rosario P; Gomes, M Teresa S R; Oliveira, J A B P

2013-01-21

153

Potentiometric responses of polymeric liquid membranes based on hydrophobic chelating agents to metal ions.  

PubMed

The effect of hydrophobicity of acidic chelating agents as sensing materials on the potentiometric responses of polymeric liquid membranes was investigated. The chelating agents tested were 8-quinolinol (HOx), dithizone (HDz), 1-(2-pyridylazo)-2-naphthol (PAN) and their alkylated analogues, 5-octyloxymethyl-8-quinolinol (HO8Q), di(phexylphenyl)thiocarbazone (C6HDz), 7-pentadecyloxy-1-(2-pyridylazo)-2-naphthol (C15PAN) and a series of N-alkylcarbonyl-N-phenylhydroxylamines (CnPHA, n = 3, 6, 9, 12). The distribution coefficients between membrane solvent and water were determined to evaluate the hydrophobicity of the agents. The potential-pH profiles of the membranes containing hydrophobic chelating agents demonstrated the generation of potentiometric responses, while less hydrophobic agents gave no response. A possible model for the generation of membrane potential is proposed. The charge separation is attained by the permselective uptake of metal cations by the chelating agent anion at membrane/solution interface, where the high hydrophobicity of the agent enables the anionic or deprotonated form of the agents to remain at the membrane/solution interface. PMID:11708143

Itoh, Y; Ueda, Y; Hirano, A; Sugawara, M; Tohda, K; Akaiwa, H; Umezawa, Y

2001-05-01

154

Theoretical investigation of the behavior of titratable groups in proteins.  

PubMed

This paper presents a theoretical analysis of the titration behavior of strongly interacting titratable residues in proteins. Strongly interacting titratable residues exist in many proteins such as for instance bacteriorhodopsin, cytochrome c oxidase, cytochrome bc(1), or the photosynthetic reaction center. Strong interaction between titratable groups can lead to irregular titration behavior. We analyze under which circumstances titration curves can become irregular. We demonstrate that conformational flexibility alone can not lead to irregular titration behavior. Strong interaction between titratable groups is a necessary, but not sufficient condition for irregular titration curves. In addition, the two interacting groups also need to titrate in the same pH-range. These two conditions together lead to irregular titration curves. The mutation of a single residue within a cluster of interacting titratable residues can influence the titration behavior of the other titratable residues in the cluster. We demonstrate this effect on a cluster of four interacting residues. This example underlines that mutational studies directed at identifying the role of a certain titratable residue in a cluster of interacting residues should always be accompanied by an analysis of the effect of the mutation on the titration behavior of the other residues. PMID:16761087

Klingen, Astrid R; Bombarda, Elisa; Ullmann, G Matthias

2006-04-12

155

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

156

The potentiometric determination of stability constants for zinc acetate complexes in aqueous solutions to 295°C  

NASA Astrophysics Data System (ADS)

A potentiometric method was used to determine the formation quotients of zinc acetate complexes in aqueous solutions from 50 to 295°C at ionic strengths of 0.03,0.3, and 1.0 m. The potentiometric titrations were carried out in an externally heated, Teflon-lined concentration cell fitted with hydrogen electrodes. Formal sodium acetate concentrations of the experimental solutions ranged from 0.001 to 0. 1 m with acetic acid to sodium acetate ratios ranging from 30 to 300. Sodium trifluoromethanesulfonate (F3CSO3Na) was used as a supporting electrolyte. Stoichiometries and formation quotients for the complexes ZnCH3COO+, Zn(CH3COO)2, and Zn(CH3COO)?3 were derived from the titration data by regression analysis. Stability constants at infinite dilution (Kn) and other relevant thermodynamic quantities were calculated for these three complexes. Logarithms for the formation constants of the general reaction Zn2+ + nCH3COO? = Zn(CH3COO)n2?n are n = 1?(1.9 ± 0.2, 50°C), (2.3 ± 0.1, 100°C), (2.8 ± 0.1, 150°C), (3.5 ± 0.1, 200°C), (4.3 ± 0.2, 250°C), (5.3 ± 0.3, 300°C); n = 2?(3.4 ± 0.1, 50°C), (4.0 ± 0.1, 100°C), (4.83 ± 0.09, 150°C), (5.9 ± 0.1, 200°C), (7.1 ± 0.1, 250°C), (8.7 ± 0.2, 300°C); n = 3?(4.1 ± 0.3, 50°C), (4.7 ± 0.3, 100°C), (5.5 ± 0.3, 150°C), (6.6 ± 0.3, 200°C), (7.9 ± 0.3, 250°C), (9.4 ± 0.3, 300°C). Calculations of zinc speciation in acetate-chloride solutions show that zinc acetate complexes should have an importance similar to zinc chloride complexes in high acetate waters where chloride to acetate molal ratios are less than about 10.

Glordano, Thomas H.; Drummond, S. E.

1991-09-01

157

Titration of the bacteriorhodopsin Schiff base involves titration of an additional protein residue.  

PubMed

The retinal protein protonated Schiff base linkage plays a key role in the function of bacteriorhodopsin (bR) as a light-driven proton pump. In the unphotolyzed pigment, the Schiff base (SB) is titrated with a pK(a) of approximately 13, but following light absorption, it experiences a decrease in the pK(a) and undergoes several alterations, including a deprotonation process. We have studied the SB titration using retinal analogues which have intrinsically lower pK(a)'s which allow for SB titrations over a much lower pH range. We found that above pH 9 the channel for the SB titration is perturbed, and the titration rate is considerably reduced. On the basis of studies with several mutants, it is suggested that the protonation state of residue Glu204 is responsible for the channel perturbation. We suggest that above pH 12 a channel for the SB titration is restored probably due to titration of an additional protein residue. The observations may imply that during the bR photocycle and M photointermediate formation the rate of Schiff base protonation from the bulk is decreased. This rate decrease may be due to the deprotonation process of the "proton-releasing complex" which includes Glu204. In contrast, during the lifetime of the O intermediate, the protonated SB is exposed to the bulk. Possible implications for the switch mechanism, and the directionality of the proton movement, are discussed. PMID:15938637

Zadok, Uri; Asato, Alfred E; Sheves, Mordechai

2005-06-14

158

Acid Rain Analysis by Standard Addition Titration.  

ERIC Educational Resources Information Center

|The standard addition titration is a precise and rapid method for the determination of the acidity in rain or snow samples. The method requires use of a standard buret, a pH meter, and Gran's plot to determine the equivalence point. Experimental procedures used and typical results obtained are presented. (JN)|

Ophardt, Charles E.

1985-01-01

159

AMPEROMETRIC TITRATION OF THORIUM SALTS WITH CUPFERRON  

Microsoft Academic Search

Thorium forms with cupferron a precipitate of ThCupâ in a wide pH ; range in the absence of strong acids and sulfates. The precipitate has a ; tendency to form a colloid, and it is necessary to use coagulants; the most ; effective is sodium chloride. Sulfosalicylic acid is a stronger masking agent ; than citric acid during thorium titration

V. D. Vasilenko; E. B. Ostrovskaya; T. S. Fomenko

1961-01-01

160

Titration Calculations with Computer Algebra Software  

ERIC Educational Resources Information Center

|This article examines the symbolic algebraic solution of the titration equations for a diprotic acid, as obtained using "Mathematica," "Maple," and "Mathcad." The equilibrium and conservation equations are solved symbolically by the programs to eliminate the approximations that normally would be performed by the student. Of the three programs,…

Lachance, Russ; Biaglow, Andrew

2012-01-01

161

Acid Rain Analysis by Standard Addition Titration.  

ERIC Educational Resources Information Center

The standard addition titration is a precise and rapid method for the determination of the acidity in rain or snow samples. The method requires use of a standard buret, a pH meter, and Gran's plot to determine the equivalence point. Experimental procedures used and typical results obtained are presented. (JN)

Ophardt, Charles E.

1985-01-01

162

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

163

A potentiometric tattoo sensor for monitoring ammonium in sweat.  

PubMed

The development and analytical characterization of a novel ion-selective potentiometric cell in a temporary-transfer tattoo platform for monitoring ammonium levels in sweat is presented. The fabrication of this skin-worn sensor, which is based on a screen-printed design, incorporates all-solid-state potentiometric sensor technology for both the working and reference electrodes, in connection to ammonium-selective polymeric membrane based on the nonactin ionophore. The resulting tattooed potentiometric sensor exhibits a working range between 10(-4) M to 0.1 M, well within the physiological levels of ammonium in sweat. Testing under stringent mechanical stress expected on the epidermis shows that the analytical performance is not affected by factors such as stretching or bending. Since the levels of ammonium are related to the breakdown of proteins, the new wearable potentiometric tattoo sensor offers considerable promise for monitoring sport performance or detecting metabolic disorders in healthcare. Such combination of the epidermal integration, screen-printed technology and potentiometric sensing represents an attractive path towards non-invasive monitoring of a variety of electrolytes in human perspiration. PMID:24098883

Guinovart, Tomàs; Bandodkar, Amay J; Windmiller, Joshua R; Andrade, Francisco J; Wang, Joseph

2013-10-15

164

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.

Wang, Yanyan; Chen, Qiang; Zeng, Xiangqun

2009-01-01

165

Recent trends in potentiometric sensor arrays--a review.  

PubMed

Nowadays there exists a large variety of ion sensors based on polymeric or solid-state membranes that can be used in a sensor array format in many analytical applications. This review aims at providing a critical overview of the distinct approaches that were developed to build and use potentiometric sensor arrays based on different transduction principles, such as classical ion-selective electrodes (ISEs) with polymer or solid-state membranes, solid-contact electrodes (SCE) including coated wire electrodes (CWE), ion-sensitive field-effect transistors (ISFETs) and light addressable potentiometric sensors (LAPS). Analysing latest publications on potentiometric sensor arrays development and applications certain problems are outlined and trends are discussed. PMID:20888446

Bratov, A; Abramova, N; Ipatov, A

2010-09-09

166

The hemes of Escherichia coli nitrate reductase A (NarGHI): potentiometric effects of inhibitor binding to narI.  

PubMed

We have potentiometrically characterized the two hemes of Escherichia coli nitrate reductase A (NarGHI) using EPR and optical spectroscopy. NarGHI contains two hemes, a low-potential heme b(L) (E(m,7) = 20 mV; g(z)() = 3.36) and a high-potential heme b(H) (E(m, 7) = 120 mV; g(z)() = 3.76). Potentiometric analyses of the g(z)() features of the heme EPR spectra indicate that the E(m,7) values of both hemes are sensitive to the menaquinol analogue 2-n-heptyl-4-hydroxyquinoline N-oxide (HOQNO). This inhibitor causes a potential-inversion of the two hemes (for heme b(L), E(m,7) = 120 mV; for heme b(H), E(m,7) = 60 mV). This effect is corroborated by optical spectroscopy of a heme b(H)-deficient mutant (NarGHI(H56R)) in which the heme b(L) undergoes a DeltaE(m,7) of 70 mV in the presence of HOQNO. Another potent inhibitor of NarGHI, stigmatellin, elicits a moderate heme b(L) DeltaE(m,7) of 30 mV, but has no detectable effect on heme b(H). No effect is elicited by either inhibitor on the line shape or the E(m,7) values of the [3Fe-4S] cluster coordinated by NarH. When NarI is expressed in the absence of NarGH [NarI(DeltaGH)], two hemes are detected in potentiometric titrations with E(m,7) values of 37 mV (heme b(L); g(z)() = 3.15) and -178 mV (heme b(H); g(z)() = 2.92), suggesting that heme b(H) may be exposed to the aqueous milieu in the absence of NarGH. The identity of these hemes was confirmed by recording EPR spectra of NarI(DeltaGH)(H56R). HOQNO binding titrations followed by fluorescence spectroscopy suggest that in both NarGHI and NarI(DeltaGH), this inhibitor binds to a single high-affinity site with a K(d) of approximately 0.2 microM. These data support a functional model for NarGHI in which a single dissociable quinol binding site is associated with heme b(L) and is located toward the periplasmic side of NarI. PMID:10504245

Rothery, R A; Blasco, F; Magalon, A; Asso, M; Weiner, J H

1999-09-28

167

Titration calorimetry standards and the precision of isothermal titration calorimetry data.  

PubMed

Current Isothermal Titration Calorimetry (ITC) data in the literature have relatively high errors in the measured enthalpies of protein-ligand binding reactions. There is a need for universal validation standards for titration calorimeters. Several inorganic salt co-precipitation and buffer protonation reactions have been suggested as possible enthalpy standards. The performances of several commercial calorimeters, including the VP-ITC, ITC200, and Nano ITC-III, were validated using these suggested standard reactions. PMID:19582227

Baranauskiene, Lina; Petrikaite, Vilma; Matuliene, Jurgita; Matulis, Daumantas

2009-06-18

168

Telephone Titration of Heart Failure Medications.  

PubMed

BACKGROUND:: In clinical practice, heart failure (HF) medications are underused and prescribed at lower than recommended doses. Telephone care is an option that could help to titrate HF medication in a timely manner. We describe our experience of a nurse-run, cardiologist- or nurse practitioner-supervised clinic to up-titrate HF medications via telephone. METHODS:: Patients with the diagnosis of HF, New York Heart Association classes I to III, were referred to a registered nurse-run, cardiologist-/nurse practitioner-supervised HF medication titration clinic. Clinical and medication data collected at enrollment to the clinic and at 3 to 6 months after optimization of HF medications in patients who did or did not reach the target doses were compared. Effect on left ventricular (LV) function was also evaluated. RESULTS:: There were 79 patients in the evaluation: 64 with HF and LV systolic dysfunction (LVSD) and the remaining 15 with HF and preserved ejection fraction (EF). Seventy-two percent of patients with LVSD were on an angiotensin-converting enzyme inhibitor (ACEI) or angiotensin receptor blocker (ARB), and 61% were on a ?-blocker at baseline, and this increased to 98% and 97%, respectively, after optimization. Target doses was achieved in 50% of patients for ACEI or ARB, and in 41% for ?-blockers. The median time to optimization was 54 days (interquartile range, 20-97 days). The average number of phone calls at the time of optimization were 5.4 (SD, 3.7), and the average number of clinic visits was 1.9 (SD, 1.3). Reasons for not reaching the target doses included hypotension, hyperkalemia, and renal dysfunction for ACEI and bradycardia for ?-blockers. Overall, the EF increased by 10% (SD, 10%) after 6 months, and 35% or greater in 42% of patients whose baseline EF was less than 35%. There were no adverse events related to the dose up-titration. CONCLUSION:: Telephonic titration of HF medications was feasible and safe and was achieved in 97% patients on ACEI/ARB and ?-blockers. Medication titration was associated with significant improvement in LV function, avoiding the need for device therapy in many patients. PMID:21127425

Steckler, Anne E; Bishu, Kalkidan; Wassif, Heba; Sigurdsson, Gardar; Wagner, Judy; Jaenicke, Connie; Vats, Shashank; Rector, Thomas; Anand, Inder S

2010-12-01

169

Potentiometric sensor for sorbic acid determination in food products  

Microsoft Academic Search

The construction, evaluation and application of a new potentiometric sensor, namely, Pt|Hg|Hg2(SOB)2 |Graphite, where SOB stands for sorbate ion, are described. This electrode has a wide linear dynamic range between 5.0×10?7 and 1.0×10?2molL?1 with a near-Nernstian slope of (?58.6±1.3) mV decade?1 and a detection limit of 4.3×10?7molL?1. The potentiometric response is independent of the pH of the solution in the

Alberto O. Santini; Helena R. Pezza; João Carloni-Filho; Rodrigo Sequinel; Leonardo Pezza

2009-01-01

170

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

171

Coulometrische titration von hypochloriten und chloraten.  

PubMed

Hypochlorite was determined by direct coulometric titration with iron(II) in an acetate buffered solution. Chlorate was titrated with titanium(III) in 2M hydrochloric acid. Amperometric indication with one and two electrodes, respectively, was used. Mixtures of hypochlorites and chlorates, e.g., in industrial electrolytes, may be analysed. On a déterminé l'hypochlorite par titrage coulométrique direct avec le fer(II) dans une solution tamponnée à l'acétate. On a titré le chlorate avec le titane(III) en acide chlorhydrique 2M. On a utilisé l'indication ampérométrique une et deux électrodes respectivement. On peut analyser des mélanges d'hypochlorites et de chlorates, par exemple dans des électrolytes industriels. PMID:18960728

Gründler, P; Holzapfel, H

1970-03-01

172

Conductometric Titration of Chlorhexidine and Proguanil  

Microsoft Academic Search

Conductometric titrations of chlorhexidine and proguanil are reported. The procedure is based on the copper-bi-guanide reaction which gives a pink solid. Studies at several pH values, and presence of NH3 and ethanol are carried out. 3 ml of 0.2 M NH3, 9ml of 0.01 M NaOH diluted to 60 mL with 15% ethanol are added to 5ml of biguenide aqueous

J. Matrtinez Calatayud; P. Campins Falcó; M. C. Pascual Martí

1986-01-01

173

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…

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

2011-01-01

174

Light-addressable potentiometric sensor for biochemical systems.  

PubMed

Numerous biochemical reactions can be measured potentiometrically through changes in pH, redox potential, or transmembrane potential. An alternating photocurrent through an electrolyte-insulator-semiconductor interface provides a highly sensitive means to measure such potential changes. A spatially selectable photoresponse permits the determination of a multiplicity of chemical events with a single semiconductor device. PMID:3375810

Hafeman, D G; Parce, J W; McConnell, H M

1988-05-27

175

Multiple applications of the light addressable potentiometric sensor  

Microsoft Academic Search

Summary form only given. The light-addressable potentiometric sensor has been used to perform a variety of fundamentally different types of measurements. This versatility is primarily a function of the mechanical configuration of the sensor. Various mechanical configurations are discussed, including flow chambers, porous membrane contact sensors, and compartmentalized sensors for measuring electrical properties of lipid bilayer membranes

J. W. Parce

1989-01-01

176

Recent trends in potentiometric sensor arrays—A review  

Microsoft Academic Search

Nowadays there exists a large variety of ion sensors based on polymeric or solid-state membranes that can be used in a sensor array format in many analytical applications. This review aims at providing a critical overview of the distinct approaches that were developed to build and use potentiometric sensor arrays based on different transduction principles, such as classical ion-selective electrodes

A. Bratov; N. Abramova; A. Ipatov

2010-01-01

177

Design of Light Addressable Potentiometric Sensors' Detecting System  

Microsoft Academic Search

A detecting system aiming to Light Addressable Potentiometric Sensors is proposed. By means of this system not only the sensitive signal data can been measured and stored real time, but also the system configuration can be set and query via the friendly User Interface. History data can be reviewed conveniently using database technology.

Lili Nie; Yunfang Jia; Ziyu Guo; Liru Ren; Huigang Liu; Jiabin Shang; Fuhai Zhang; Hongli Tian; Tao Wang; Keli Xing

2010-01-01

178

Light-addressable potentiometric sensor for biochemical systems  

Microsoft Academic Search

Numerous biochemical reactions can be measured potentiometrically through changes in pH, redox potential, or transmembrane potential. An alternating photocurrent through an electrolyte-insulator-semiconductor interface provides a highly sensitive means to measure such potential changes. A spatially selectable photoresponse permits the determination of a multiplicity of chemical events with a single semiconductor device.

Dean G. Hafeman; J. Wallace Parce; Harden M. McConnell

1988-01-01

179

Revised potentiometric-surface map, Yucca Mountain and vicinity, Nevada.  

National Technical Information Service (NTIS)

The revised potentiometric-surface map presented in this report updates earlier maps of the Yucca Mountain area using mainly 1988 average water levels. Because of refinements in the corrections to the water-level measurements, these water levels have incr...

E. M. Ervin R. R. Luckey D. J. Burkhardt

1994-01-01

180

Light-addressable potentiometric sensor for biochemical systems  

NASA Astrophysics Data System (ADS)

Numerous biochemical reactions can be measured potentiometrically through changes in pH, redox potential, or transmembrane potential. An alternating photocurrent through an electrolyte-insulator-semiconductor interface provides a highly sensitive means to measure such potential changes. A spatially selectable photoresponse permits the determination of a multiplicity of chemical events with a single semiconductor device.

Hafeman, Dean G.; Parce, J. Wallace; McConnell, Harden M.

1988-05-01

181

New challenges for pharmaceutical formulations and drug delivery systems characterization using isothermal titration calorimetry.  

PubMed

Long viewed as the 'method of choice' for characterizing thermodynamics and stoichiometry of molecular interactions, with high sensitivity, isothermal titration calorimetry (ITC) has been applied to many areas of pharmaceutical analysis. This review highlights ITC employment to measure binding thermodynamics and their use for pharmaceutical formulations and drug delivery system characterization particularly cyclodextrin-guest interactions, investigation of micellar-based systems, polyelectrolytes, nucleic acid interactions with multivalent cations and the optimization of DNA targeting and delivery. Furthermore, the potential of ITC for the characterization of different functionalities carried by nanoparticles as well as their interaction with living systems was outlined. PMID:18617012

Bouchemal, Kawthar

2008-07-19

182

Association quotients of aluminum sulphate complexes in NaCl media from 50 to 125 C: Results of a potentiometric and solubility study  

SciTech Connect

The speciation and molal formation quotients for the complexation of aluminum with sulphate were measured based on potentiometric and solubility experiments. Potentiometric titrations, utilizing a hydrogen-electrode concentration cell, were performed from 50 to 125 C at ionic strengths of 0.1, 0.3 and 1.0 molal in aqueous NaCl media. Two aluminum-sulphate species, AlSO{sub 4}{sup +} and Al(SO{sub 4}){sub 2}{sup {minus}}, were identified from the titration data and the formation quotients for these species were modeled by empirical equations to describe their temperature and ionic strength dependencies. Thermodynamic parameters for the complexation reactions were obtained by differentiating the empirical equations with respect to temperature. The thermodynamic quantities obtained for the formation of AlSO{sub 4}{sup +} at 50 C and infinite dilution are: logK{sub 1} = 3.7 {+-} 0.4, {Delta}H{sub 1}{degree} = {minus}10 {+-} 30 kJ/mol, {Delta}S{sub 1}{degree} = 40 {+-} 100 J/K{center_dot}mol and {Delta}C{sub p 1}{degree} = 1900 {+-} 800 J/K{center_dot}mol; whereas the values for Al(SO{sub 4}){sub 2}{sup {minus}} are: logK{sub 2} = 5.6 {+-} 0.7, {Delta}H{sub 2}{degree} = 10 {+-} 50 kJ/mol, {Delta}S{sub 2}{degree} = 100 {+-} 100 J/K{center_dot}mol and {Delta}C{sub p 2}{degree} = 2800 {+-} 800 J/K{center_dot}mol. A solubility study, which was undertaken to verify the 50 C potentiometric data, was performed by reacting powdered gibbsite (Al(OH){sub 3}) with sulphate solutions at 10{sup {minus}3.5} and 10{sup {minus}4} molal H{sup +}, total sulphate concentrations from 0.005 to 0.080 molal, and 0.1 and 1.0 molal ionic strength in aqueous NaCl media. The results of the solubility study are in good agreement with the potentiometric data and establish that Al-sulphate complexation substantially enhances the equilibrium solubility of gibbsite.

Ridley, M.K.; Kettler, R.M. [Univ. of Nebraska, Lincoln, NE (United States). Dept. of Geology; Wesolowski, D.J.; Palmer, D.A. [Oak Ridge National Lab., TN (United States). Chemical and Analytical Sciences Div.

1999-02-01

183

Alkaline Titrations of poly(dG-dC)·poly(dG-dC): Microemulsion Versus Solution Behavior  

Microsoft Academic Search

PolyGC was titrated with a strong base in the presence of increasing concentrations of NaCl (from 0.00 to 0.60M) either in water solution or with the polynucleotide solubilized in the aqueous core of reverse micelles, i.e., the cationic quaternary water-in-oil microemulsion CTAB\\/n-hexane\\/n-pentanol\\/water. The results for matched samples in the two media were compared. CD and UV spectroscopies and, for the

Marta Airoldi; Giuseppe Gennaro; Marcello Giomini; Anna Maria Giuliani; Mauro Giustini

2007-01-01

184

Determining enzyme kinetics via isothermal titration calorimetry.  

PubMed

Isothermal titration calorimetry (ITC) has emerged as a powerful tool for determining the thermodynamic properties of chemical or physical equilibria such as protein-protein, ligand-receptor, and protein-DNA binding interactions. The utility of ITC for determining kinetic information, however, has not been fully recognized. Methods for collecting and analyzing data on enzyme kinetics are discussed here. The step-by-step process of converting the raw heat output rate into the kinetic parameters of the Michaelis-Menten equation is explicitly stated. The hydrolysis of sucrose by invertase is used to demonstrate the capability of the instrument and method. PMID:23423886

Demarse, Neil A; Killian, Marie C; Hansen, Lee D; Quinn, Colette F

2013-01-01

185

Probing differential Ag+-nucleobase interactions with isothermal titration calorimetry (ITC): Towards patterned DNA metallization  

NASA Astrophysics Data System (ADS)

DNA has been successfully used as a scaffold for the fabrication of metallic nanowires, primarily based on the electrostatic complexation and reduction of the metal cations on the negatively charged sugar-phosphate backbone. Here, we probe the differential binding affinities of nucleobases for silver ions using sensitive isothermal titration calorimetry (ITC) measurements of the reaction enthalpies, which go in order: C > G > A >= T. Using the disparity between the interaction of cytosine (strong binding) and thymine (weak binding) with silver ions, we have successfully generated silver nanoparticle doublets and triplets on custom-made oligonucleotides, C30-T40-C30 and C20-T20-C20-T20-C20, respectively. Thus, a new and simple method of generating metallized DNA wires is presented, based entirely on the nucleotide sequence of DNA. The concept could be extended to other cations and complex DNA sequences in order to achieve intricately patterned DNA constructs.

Shukla, Sourabh; Sastry, Murali

2009-09-01

186

The complexation of alkaline cations by crown ethers and cryptands in acetone  

SciTech Connect

Stability constants and thermodynamic values for the complex formation of alkali ions by crown ethers, diaza crown ethers and cryptands have been measured by means of potentiometric and calorimetric titrations in acetone as solvent. The interactions between the ligands and solvent molecules play an important role for the complex formation. Cryptands form the most stable complexes with alkali ions if inclusion complexes are formed. Even in the case that the salts are not completely dissociated in acetone, the presence of ion pairs does not influence the calculated values of the stability constants.

Buschmann, H.J.; Cleve, E.; Schollmeyer, E. [Deutsches Textilforschungszentrum Nord-West, Krefeld (Germany)

1994-05-01

187

Potentiometric sensors using cotton yarns, carbon nanotubes and polymeric membranes.  

PubMed

A simple and generalized approach to build electrochemical sensors for wearable devices is presented. Commercial cotton yarns are first turned into electrical conductors through a simple dyeing process using a carbon nanotube ink. These conductive yarns are then partially coated with a suitable polymeric membrane to build ion-selective electrodes. Potentiometric measurements using these yarn-potentiometric sensors are demonstrated. Examples of yarns that can sense pH, K(+) and NH4(+) are presented. In all cases, these sensing yarns show limits of detection and linear ranges that are similar to those obtained with lab-made solid-state ion-selective electrodes. Through the immobilization of these sensors in a band-aid, it is shown that this approach could be easily implemented in a wearable device. Factors affecting the performance of the sensors and future potential applications are discussed. PMID:23775189

Guinovart, Tomàs; Parrilla, Marc; Crespo, Gastón A; Rius, F Xavier; Andrade, Francisco J

2013-06-18

188

Direct potentiometric determination of starch using a platinum redox sensor.  

PubMed

Here, we describe the development of a platinum redox sensor for the direct potentiometric quantification of starch in solution. The sensor measures the decrease in free triiodide ion after it complexes with starch to form a starch-triiodide complex. This decrease was, therefore, correlated with starch concentration, and the composition and stability of the potassium triiodide solution were optimised. The starch-triiodide complex was characterized potentiometrically at variable starch and triiodide concentrations. We also propose a response mechanism for the platinum redox sensor towards starch and an appropriate theoretical model. The optimised method exhibited satisfactory accuracy and precision and was in good agreement with a standard spectrophotometric method. The sensor was tested over a range of 0.4-9 mg starch, with recoveries ranging from 97.8% to 103.4% and a detection limit of 0.01 mg starch. PMID:23265448

Saka?, Nikola; Sak-Bosnar, Milan; Horvat, Marija

2012-11-08

189

PVC matrix membrane sensor for potentiometric determination of dodecylsulfate  

Microsoft Academic Search

The construction and performance characteristics of a new potentiometric PVC membrane sensor for the determination of sodium dodecyl sulfate (SDS) are described. The sensor was based on the use of an N-cetyl-N,N,N trimethyl ammonium (CTA) dodecyl sulfate (DS) ion pair as ion exchange sites in PVC matrix in the presence of o-nitrophenyl octylether as plasticiser. The sensor exhibited a fast,

Gamal A. E. Mostafa

2008-01-01

190

Comparison of enzyme immobilisation methods for potentiometric phosphate biosensors  

Microsoft Academic Search

The development of two phosphate biosensors is described and compared for potentiometric detection of phosphate. Purine nucleoside phosphorylase (PNP) and xanthine oxidase (XOD) were co-immobilised by chemical cross-linking with glutaraldehyde (GLA) and bovine serum albumin (BSA), and via entrapment into polypyrrole (PPy) films by galvanostatic polymerisation. The BSA-GLA film was made with 4.5% v\\/v GLA and 6.8% w\\/v BSA with

A. T. Lawal; S. B. Adeloju

2009-01-01

191

Simulation of light addressable Potentiometric sensors based on MEDICI  

Microsoft Academic Search

Light addressable Potentiometric sensors (LAPS) are the biochemically sensitive semiconductor devices. Its working principles, the charge-distribution models of the electrolyte-insulator (EI) interface and its incorporation with semiconductor's photoelectric effects, are summarized. Then back illuminated LAPS with the structure of Si3N4\\/Si02\\/Si is simulated based on MEDICI, one of Synopsys' device simulation tools. The simulated results are compared with what obtained by

Yunfang Jia; Lijun Ma; Qiaoshan Chen; Jiadai Liu; Keli Xing; Wencheng Niu

2010-01-01

192

Alternative sensor materials for light-addressable potentiometric sensors  

Microsoft Academic Search

Ta2O5 and porous Si were investigated as alternative sensor materials for the light-addressable potentiometric sensor (LAPS). The Ta2O5 LAPS, prepared by the pulsed laser deposition (PLD) technique, showed a high pH sensitivity of 57.5mV\\/pH and a good linearity. Porous Si was prepared by anodic etching of Si in a mixture of HF and ethanol. The porous Si LAPS with a

T Yoshinobu; H Ecken; A Poghossian; H Lüth; H Iwasaki; M. J Schöning

2001-01-01

193

Light-Addressable Potentiometric Sensors - Model and Experiments  

Microsoft Academic Search

In the recent years reliable technologies for the production of ion-sensitive integrated devices compatible with conventional MOS technologies, have been developed. In this work, a numerical methodology suitable for device-level analysis of Light-Addressable Potentiometric Sensors (LAPS) is presented. The formulation of charge transport equations adopted in the present model accounts for the charge layers at the electrolyte-insulator interface and for

L. Colalongo; G. Verzellesi; D. Passeri; A. Lui; M. Rudan; P. Ciampolini

1996-01-01

194

Portable light-addressable potentiometric sensor (LAPS) for multisensor applications  

Microsoft Academic Search

A novel design of the light-addressable potentiometric sensor (LAPS) for realisation of a portable multisensor device is presented. Light sources and electronics including an oscillator, a multiplexer, a pre-amplifier and a high-pass filter are encapsulated in a pen-shaped case, on which the sensor plate is mounted. This sensor device is capable of measuring up to four different ion species by

T. Yoshinobu; M. J. Schöning; R. Otto; K. Furuichi; Yu. Mourzina; Yu. Ermolenko; H. Iwasaki

2003-01-01

195

Light Addressable Potentiometric Biosensor for the Detection of Anticholinesterases  

Microsoft Academic Search

Biotinylated acetylcholinesterase (AChE) from Eel was immobilized to a biotinylated cellulose nitrate membrane via a streptavidin bridge. Using a light addressable potentiometric sensor (LAPS), enzyme activity was determined as a function of substrate concentration (i.e. acetylcholine) and amount of enzyme immobilized to the membrane. This biosensor was also evaluated for its potential to detect organophosphate (OP) anticholinesterases (antiChEs).

Kim R. Rogers; Marlene Foley; Stephen Alter; Philip Koga; Mohyee Eldefrawi

1991-01-01

196

Automated titration method for use on blended asphalts  

SciTech Connect

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

197

On the invention of conductimetric titration.  

PubMed

In contrast to the earlier statement of one of the authors according to which conductimetric titration was invented by Küster and Grüters in 1903, it is shown that Ostwald made use of this analytical method as early as the nineties of the past century. Prior to Ostwald's work, however, papers appeared in which conductimetric curves were shown, with statements about their different characteristics in the case of reaction between weak and strong acids and bases. The first of these seems to be due to Kohlrausch [together with one of his co-workers, Kreichgauer (1885)]. It does not seem to have occurred to them, however, to use this phenomenon for the purposes of analytical chemistry, namely for titrimetry. PMID:18963516

Szabadváry, F; Chalmers, R A

1983-12-01

198

Computational titrations of linear and branched polyethyleneimine  

NASA Astrophysics Data System (ADS)

Despite a great deal of interest in polyethyleneimine (PEI) for its potential use as a gene therapy vector, the protonation state of this polycation is currently not well understood. PEI is rare among polyelectrolytes as every third atom along the backbone of the polymer is a protonable nitrogen. The closeness of these potentially charged sites can lead to high electrostatic repulsion and a large shift in the effective pKa of the amine groups as the degree of protonation increases. Previous experimental and theoretical estimates of the degree of protonation of PEI under physiological conditions have ranged from 0.15 to 0.80. Here, we perform computational titrations on coarse-grained models of both branched and linear PEI under various conditions. Chain length, degree of branching, salt concentration, and the solvent dielectric constant are varied to determine how these factors influence the protonation of PEI.

Ziebarth, Jesse; Wang, Yongmei

2009-03-01

199

Manganese(III) Porphyrin-based Potentiometric Sensors for Diclofenac Assay in Pharmaceutical Preparations  

PubMed Central

Two manganese(III) porphyrins: manganese(III) tetraphenylporphyrin chloride and manganese(III)-tetrakis(3-hydroxyphenyl)porphyrin chloride were tested as ionophores for the construction of new diclofenac–selective electrodes. The electroactive material was incorporated either in PVC or a sol–gel matrix. The effect of different plasticizers and additives (anionic and cationic) on the potentiometric response was studied. The best results were obtained for the PVC membrane plasticized with dioctylphtalate and having sodium tetraphenylborate as a lipophilic anionic additive incorporated. The sensor response was linear in the concentration range 3 × 10?6 – 1 × 10?2 M with a slope of ?59.7 mV/dec diclofenac, a detection limit of 1.5 × 10?6 M and very good selectivity coefficients. It was used for the determination of diclofenac in pharmaceutical preparations, by direct potentiometry. The results were compared with those obtained by the HPLC reference method and a good agreement was found between the two methods.

Vlascici, Dana; Pruneanu, Stela; Olenic, Liliana; Pogacean, Florina; Ostafe, Vasile; Chiriac, Vlad; Pica, Elena Maria; Bolundut, Liviu Calin; Nica, Luminita; Fagadar-Cosma, Eugenia

2010-01-01

200

Determination of pethidine hydrochloride using potentiometric coated graphite and carbon paste electrodes.  

PubMed

A new approach for lowering the detection limit of a pethidine ion-selective electrode is presented. A coated graphite (CGE) and carbon paste (CPE) electrodes for pethidine ions based on pethidine-phosphotungstate (PD-PT) as ion-pair complex are described. The sensors exhibit a Nernstian slope of 58.1 and 54.2 mVdecade(-1) for pethidine ion over a wide concentration range from 2.6 × 10(-7) to 1.0 × 10(-2) M and 2.1 × 10(-6) to 1.0 × 10(-2) M with a detection limit of 1.8 × 10(-7) M and 7.3 × 10(-7) M for pethidine coated graphite (PD-CGE) and pethidine carbon paste electrode (PD-CPE), respectively. These sensors exhibited a fast response time (about 5-8 s) and good stability. The standard electrode potentials, E(o) , were determined at different temperatures and used to calculate the isothermal temperature coefficient (dE(o) /dT) of the PD-CGE and PD-CPE, which was 0.0062 and 0.0071 V/ °C, respectively. Selectivity coefficients, determined by matched potential method (MPM) and separate solution method (SSM), showed high selectivity for pethidine hydrochloride (PDCl) over a large number of inorganic cations, organic cations, sugars, urine components, and some common drug excipients. The sensors were applied for determination of PDCl in ampoule and in spiked urine samples using potentiometric determination, standard addition and the calibration curve methods. The results obtained were satisfactory with excellent percentage recovery comparable and sometimes better than those obtained by other routine methods for the assay. PMID:21538999

Abu-Shawish, Hazem M; Dalou, Ayoub A; Ghalwa, Nasser Abu; Khraish, Ghada I; Hammad, Jehad; Basheer, Abdel-Hakem

2011-05-03

201

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

202

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

203

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

204

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

205

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

206

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

Microsoft Academic Search

This report details a geostatistical analysis of potentiometric data from the Wolfcamp 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 Wolfcamp data are found to be well explained by

W. V. Harper; J. M. Furr

1986-01-01

207

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

208

Determination of chloride by multisyringe flow injection analysis and sequential injection analysis with potentiometric detection  

Microsoft Academic Search

This paper reports for the first time a multisyringe flow injection analysis (MSFIA) method with potentiometric detection for the automated determination of chloride in waters. The methodology developed was applied to the determination of chloride in mineral, tap and waste waters and the results achieved were compared with those obtained by a potentiometric sequential injection analysis (SIA) method reported in

A Andrade-Eiroa; J. A Erustes; R Forteza; V Cerdá; J. L. F. C Lima

2002-01-01

209

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

210

Modeling and simulation of light-addressable potentiometric sensors  

Microsoft Academic Search

Results of modeling and theoretical simulation of the influence of intensity-modulated irradiation on the light-addressable\\u000a potentiometric sensors based on the electrolyte-insulator-semiconductor and electrolyte-membrane-insulator-semiconductor structures\\u000a are presented. A theoretical model for measuring a.c. photocurrent is developed based on the assumption that under modulated\\u000a irradiation the conductivity of the semiconductor depletion layer is modulated. The electric equivalent a.c. schemes are presented\\u000a and

F. V. Gasparyan

2010-01-01

211

Magnetic Nanoparticles Produced in Spontaneous Cationic-Anionic Vesicles: Room Temperature Synthesis and Characterization  

Microsoft Academic Search

Unilamellar vesicles formed spontaneously by forming solutions of single-tailed cationic and anionic surfactants [cetyltrimethylammonium bromide (CTAB) and dodecylbenzenesulfonic acid (HDBS), respectively] have been used as reactors for the direct, room temperature synthesis of nanometer-sized magnetic particles within their internal cores. A micellar anionic surfactant solution was titrated slowly into a micellar cationic surfactant solution containing ferrous chloride, forming defect-free unilamellar

Iskandar I. Yaacob; Anthony C. Nunes; Arijit Bose

1995-01-01

212

A novel potentiometric method for the determination of real crosslinking ratio of poly(aspartic acid) gels.  

PubMed

In order to obtain nontoxic functional polymer gels for biomedical applications, chemically crosslinked poly(aspartic acid) gels have been prepared using 1,4-diaminobutane as crosslinker. The presence of COOH and amino groups on the network chains renders these gels pH sensitive. Due to the specific hydrophobic-hydrophilic balance, these gels show a significant volume transition at a well-defined pH close to the pK value of uncrosslinked poly(aspartic acid). Since the magnitude of volume change critically depends on the degree of crosslinking, it is an important task to determine the topological characteristics of these networks. A novel method based on potentiometric acid-base titration has been developed to assess the crosslinking ratio, excluding physical crosslinks and entanglements. It turned out that only 25% of all crosslinker molecules forms real crosslinks between the poly(aspartic acid) chains; the rest react with one of its functional groups and forms short pendant side chains. At a nominal crosslinking ratio of 0.1, the number average molecular mass between crosslinks is found to be M(c) = 2300. PMID:19761876

Torma, Viktória; Gyenes, Tamás; Szakács, Zoltán; Zrínyi, Miklós

2009-09-15

213

Antidepressant up-titration: pharmacological and psychological considerations.  

PubMed

The use of antidepressant up-titration in starting therapies is useful in reducing side effects, but can induce delays in clinical response. Several aspects concerning slow or more aggressive titration have to be considered when using this strategy, such as pharmacological aspects (e.g., synaptic up-regulation) and psychological/clinical aspects (e.g., adherence to antidepressant treatment, and the temperament and expectations of patients). Data from the literature are controversial, and so the choice between rapid and slow titration must be tailored more to the patient, rather than to the drug. PMID:22862155

Torta, Riccardo G V

2012-08-06

214

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

215

Transport of Divalent Cations  

PubMed Central

The cation exchange capacity of the intact xylem vessels in cut shoots of papyrus (Cyperus papyrus spec.) has been determined. The cation exchange capacity is independent of the cation concentration in the transpiration stream, and is equal for Ca and Co. The high value of the cation exchange capacity (0.6 to 1 × 10?7 equivalents per square centimeter vessel wall surface) leads to the hypothesis that the porous structure of the vessel wall, and not only the inner vessel wall surface, acts as a cation exchanger. Differences between anion ([32P]phosphate, [45Ca]EDTA2?, [115Cdm]-EDTA2?), and cation ([45Ca]2+, [115Cdm]2+) movement are explained in terms of transport with the transpiration flux or by exchange reactions. The competition between exchange sites and natural or synthetic ligands for the divalent cations is discussed. Images

Van de Geijn, Siebe C.; Petit, Charles M.

1979-01-01

216

Total Acid Value Titration of Hydrotreated Biomass Fast Pyrolysis Oil: Determination of Carboxylic Acids and Phenolics with Multiple End-Point Detection  

SciTech Connect

Total acid value titration has long been used to estimate corrosive potential of petroleum crude oil and fuel oil products. The method commonly used for this measurement, ASTM D664, utilizes KOH in isopropanol as the titrant with potentiometric end point determination by pH sensing electrode and Ag/AgCl reference electrode with LiCl electrolyte. A natural application of the D664 method is titration of pyrolysis-derived bio-oil, which is a candidate for refinery upgrading to produce drop in fuels. Determining the total acid value of pyrolysis derived bio-oil has proven challenging and not necessarily amenable to the methodology employed for petroleum products due to the different nature of acids present. We presented an acid value titration for bio-oil products in our previous publication which also utilizes potentiometry using tetrabutylammonium hydroxide in place of KOH as the titrant and tetraethylammonium bromide in place of LiCl as the reference electrolyte to improve the detection of these types of acids. This method was shown to detect numerous end points in samples of bio-oil that were not detected by D664. These end points were attributed to carboxylic acids and phenolics based on the results of HPLC and GC-MS studies. Additional work has led to refinement of the method and it has been established that both carboxylic acids and phenolics can be determined accurately. Use of pH buffer calibration to determine half-neutralization potentials of acids in conjunction with the analysis of model compounds has allowed us to conclude that this titration method is suitable for the determination of total acid value of pyrolysis oil and can be used to differentiate and quantify weak acid species. The measurement of phenolics in bio-oil is subject to a relatively high limit of detection, which may limit the utility of titrimetric methodology for characterizing the acidic potential of pyrolysis oil and products.

Christensen, E.; Alleman, T. L.; McCormick, R. L.

2013-01-01

217

Adsorption microcalorimetry used to study interfacial aggregation of quaternary ammonium surfactants (zwitterionic and cationic) on powdered silica supports in dilute aqueous solutions  

Microsoft Academic Search

Titration microcalorimetry has been used to compare interfacial aggregation of some zwitterionic and cationic quaternary ammonium surfactants on powdered silica substrates with micellisation in free aqueous solution. Enthalpy of dilution measurements allowed determining the molar enthalpies of micellisation for two zwitterionic amphiphiles, (dodecyldimethylammonio)butanoate and (dodecyl dimethylammonio)-1-propanesulfonate, and two cationics, benzyldimethyldodecylammonium bromide (BDDAB) and tetradecyltrimethylammonium bromide (TTAB). The effect of temperature

Jerzy Zajac

2000-01-01

218

Microscope Titration and Extraction of DNA from Liver.  

ERIC Educational Resources Information Center

|Describes a simple and inexpensive, one-period activity to extract DNA to make the study of DNA less abstract. A microscope titration is used to determine when cells are ready for DNA extraction. (PR)|

Mayo, Lois T.; And Others

1993-01-01

219

Microscope Titration and Extraction of DNA from Liver.  

ERIC Educational Resources Information Center

Describes a simple and inexpensive, one-period activity to extract DNA to make the study of DNA less abstract. A microscope titration is used to determine when cells are ready for DNA extraction. (PR)

Mayo, Lois T.; And Others

1993-01-01

220

A Titration Technique for Demonstrating a Magma Replenishment Model.  

ERIC Educational Resources Information Center

|Conductiometric titrations can be used to simulate subduction-setting volcanism. Suggestions are made as to the use of this technique in teaching volcanic mechanisms and geochemical indications of tectonic settings. (JN)|

Hodder, A. P. W.

1983-01-01

221

The hydrolysis and precipitation of Pd(II) in 0.6 mol kg-1 NaCl: A potentiometric, spectrophotometric, and EXAFS study  

SciTech Connect

The hydrolysis of palladium was investigated in 0.6 mol•kg-1 NaCl at 298.2 K. Potentiometric titrations of solutions at various total concentrations of palladium(II) revealed that dilute (millimolar) conditions can be used to monitor the proton release due to hydrolysis reactions up to 2 protons per palladium(II) as long as the equilibration time is kept small. Spectrophotometric titrations were used to corroborate the homogeneous changes in speciation for the PdCl3OH2- species and to extract its correlative molar absorption coefficients in the 210-320 nm range. The molar absorption coefficients are similar to those of PdCl42- but exhibit a broader distribution of excitation energies resulting from the blue shift of the dominant charge transfer bands due to the presence of OH-. The longer-term potentiometric titrations systematically yielded, on the other hand, precipitates which matured over a period of 6 weeks and resulted in a more extensive release of protons to the solution. Precipitation experiments at six different total palladium(II) concentrations in the 3-11 pH range showed the dominant precipitating phase as Pd(OH)1.72Cl0.28. The coordination environment of Pd in this solid was investigated by extended X-ray absorption fine structure spectroscopy (EXAFS) and yielded an average 1.75 O and 0.25 Cl per Pd atoms with a Pd-O distance of 2.0 Å and Pd-Cl of 2.1 Å. Finally, the precipitation experiments showed the final products to be of larger solubility than a literature Pd(OH)2 solubility study in which the KCl media induced a solid phase transformation to Pd(OH)1.72Cl0.28. Polynuclear complexes Pdq(OH)r2q-r with q=r=[3,9] explain the combined precipitation and hydrolysis data and may represent subsets of [Pd(OH)2]n and/or [Pd(OH)1.72Cl0.28]n chains coiled into nanometer-sized spheroids previously described in the literature.

Boily, Jean F.; Seward, Terry M.; Charnock, John M.

2007-10-15

222

Electrochemical properties of the solvent SbCl/sub 3/-AlCl/sub 3/-N-(1-butyl)pyridinium chloride and electrochemical and spectroelectrochemical studies of the solute 9,10-dimethylanthracene. [Oxidation of 9,10-dimethylanthracene to radical cation  

SciTech Connect

Specific conductivities of the compositions (mole %) 60:19:21 (basic) and 60:21:19 (acidic) SbCl/sub 3/-AlCl/sub 3/-BPCl, measured over the temperature range 24 to 100/sup 0/C, varied from 0.00395 to 0.02759 S cm/sup -1/. Viscosities of the 60:21:19 and 60:19:21 melts were 22.8 +- 0.7 and 31.5 +- 0.9 cp, respectively, at 25.1 +- 0.5/sup 0/C. For a potentiometric titration between the compositions 60:18:22 and 60:22:18 with SbCl/sub 3/ fixed at 60 mol %, the potential of the Sb(III)/Sb(0) couple increased by 0.43 V at 27/sup 0/C. Current-overvoltage curves for the oxidation of antimony metal in a 60:21:19 melt at an Sb rod electrode displayed Tafel behavior. The feasibility of performing electrochemical studies in these media was demonstrated using cyclic voltammetry, differential pulse polarography and double potential-step chronocoulometry to elucidate the electrochemical behavior of 9,10-dimethylanthracene (DMA) in the 60:19:21 melt. The solute was reversibly oxidized to its radical cation at an anodic peak potential of + 0.50 V relative to the reference electrode (SbCl/sub 3/-BPCl(l), sat. SbCl/sub 3//Sb at 27/sup 0/C. Spectroelectrochemical experiments on DMA using an optical multichannel spectrometer over the range 479 to 984 nm are reported. The spectrum of the DMA radical cation has four bands with the most intense at 678 nm.

Chapman, D.M.; Smith, G.P.; Sorlie, M.; Petrovic, C.; Mamantov, G.

1983-01-01

223

Cyclic alternating pattern and positive airway pressure titration  

Microsoft Academic Search

Objective: To demonstrate that stability of the upper airway during continuous positive airway pressure (CPAP) titration is influenced by the microstructure of sleep as defined by the cyclic alternating pattern (CAP).Methods: Retrospective review of 12 CPAP titration records. The patterns of flow-limitation during CPAP at subtherapeutic pressures were characterized as ‘stable’ (persistent and non-progressive inspiratory flow limitation) or ‘unstable’ (progressive

Robert Joseph Thomas

2002-01-01

224

Coulometric microflow titrations with chemiluminescent and amperometric equivalence point detection  

Microsoft Academic Search

A coulometric flow titration with electrogenerated bromine was combined with chemiluminescent and amperometric flow detection to determine low concentrations of hydrazine and ammonium. Hydrazine can be precisely titrated in the range between 2?M and 1.1mM with chemiluminescence detection of the equivalence points with relative standard deviations between 1.9 and 0.4% (n=5, ?=0.05). 60nM is the lowest concentration of hydrazine, which

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

2000-01-01

225

Investigation of ligand binding to the multidrug resistance protein EmrE by isothermal titration calorimetry.  

PubMed

Escherichia coli multidrug resistance protein E (EmrE) is an integral membrane protein spanning the inner membrane of Escherichia coli that is responsible for this organism's resistance to a variety of lipophilic cations such as quaternary ammonium compounds (QACs) and interchelating dyes. EmrE is a 12-kDa protein of four transmembrane helices considered to be functional as a multimer. It is an efflux transporter that can bind and transport cytoplasmic QACs into the periplasm using the energy of the proton gradient across the inner membrane. Isothermal titration calorimetry provides information about the stoichiometry and thermodynamic properties of protein-ligand interactions, and can be used to monitor the binding of QACs to EmrE in different membrane mimetic environments. In this study the ligand binding to EmrE solubilized in dodecyl maltoside, sodium dodecyl sulfate and reconstituted into small unilamellar vesicles is examined by isothermal titration calorimetry. The binding stoichiometry of EmrE to drug was found to be 1:1, demonstrating that oligomerization of EmrE is not necessary for binding to drug. The binding of EmrE to drug was observed with the dissociation constant (K(D)) in the micromolar range for each of the drugs in any of the membrane mimetic environments. Thermodynamic properties demonstrated this interaction to be enthalpy-driven with similar enthalpies of 8-12 kcal/mol for each of the drugs in any of the membrane mimetics. PMID:15501941

Sikora, Curtis W; Turner, Raymond J

2004-10-22

226

A surface complex reaction model for the pH-dependence of corundum and kaolinite dissolution rates  

Microsoft Academic Search

Comparison of experimental and theoretical potentiometric titrations of kaolinite at 25°C indicates that the adsorption of H + and OH - ions to the mineral surface are metal cation specific and that the net adsorption can be modeled in terms of the constituent oxide components. We conclude, from the potentiometric, electrophoretic, and dissolution rate data presented in this paper, that

Susan A. Carroll-Webb; John V. Walther

1988-01-01

227

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

228

Modeling potentiometric measurements in topological insulators including parallel channels  

NASA Astrophysics Data System (ADS)

The discovery of spin-polarized states at the surface of three-dimensional topological insulators (TI) like Bi2Te3 and Bi2Se3 motivates intense interests in possible electrical measurements demonstrating unique signatures of these unusual states. Here we show that a three-terminal potentiometric set-up can be used to probe them by measuring the voltage change of a detecting magnet upon reversing its magnetization. We present numerical results using a nonequilibrium Green's function (NEGF)-based model to show the corresponding signal quantitatively in various transport regimes. We then provide an analytical expression for the resistance (the measured voltage difference divided by an applied current) that agrees with NEGF results well in both ballistic and diffusive limits. This expression is applicable to TI surface states, two-dimensional electrons with Rashba spin-split bands, and any combination of multiple channels, including bulk parallel states in TI, which makes it useful in analyzing experimental results.

Hong, Seokmin; Diep, Vinh; Datta, Supriyo; Chen, Yong P.

2012-08-01

229

CO2 Selective Potentiometric Sensor in Thick-film Technology  

PubMed Central

A potentiometric sensor device based on screen-printed Nasicon films was investigated. In order to transfer the promising sensor concept of an open sodium titanate reference to thick film technology, “sodium-rich” and “sodium-poor” formulations were compared. While the “sodium-rich” composition was found to react with the ion conducting Nasicon during thermal treatment, the “sodium-poor” reference mixture was identified as an appropriate reference composition. Screen-printed sensor devices were prepared and tested with respect to CO2 response, reproducibility, and cross-interference of oxygen. Excellent agreement with the theory was observed. With the integration of a screen-printed heater, sensor elements were operated actively heated in a cold gas stream.

Sahner, Kathy; Schulz, Anne; Kita, Jaroslaw; Merkle, Rotraut; Maier, Joachim; Moos, Ralf

2008-01-01

230

Guanidinium-based potentiometric SO2 gas sensor.  

PubMed

An SO2 gas sensor was developed by using a hydrogen sulfite-selective electrode positioned behind a gas-permeable membrane (GPM). The hydrogen sulfite-selective electrode was prepared by incorporating a multicyclic guanidinium ionophore in a plasticized poly(vinyl chloride) membrane. This gas sensor presents important advantages over the conventional Severinghaus-type SO2 gas sensor that contains a pH electrode immersed in an internal solution behind the GPM. The Severinghaus gas sensor suffers interferences from weak acids that can cross the GPM as gases and change the pH of the internal solution. In contrast, in the proposed sensor, the excellent selectivity of the HSO3- electrode and the ability of the GPM to discriminate gaseous from nongaseous species combine to generate the most selective potentiometric SO2 gas sensor reported to date. PMID:9921127

Mowery, M D; Hutchins, R S; Molina, P; Alajarín, M; Vidal, A; Bachas, L G

1999-01-01

231

Technological aspects of potentiometric BSC-type microsensor fabrication  

NASA Astrophysics Data System (ADS)

The reported back-side contact sensor were fabricated using a standard IC technology. The silver/silver chloride layers were deposited using electrochemical technique. The sensor chips were passivated with silicon nitride layer deposited by LPCVD, which ensure the stability of measurements. Preliminary examination of prepared sensor included the evaluation of their electrical properties and potentiometric response toward chloride. It was found that 19 sensors among 20 exhibited fast and reversible response toward chloride. Near theoretical slopes were obtained over the 10-4- 10-1 M chloride concentration range. The response time was shorter than 10S. The statistical evaluation, the calibration curves and the dynamic response of 20 sensors tested at the same time indicates that the proposed technology ensures preparation of sensor chips in a very reproducible way.

Pijanowska, Dorota; Wygladacz, Katarzyna; Jazwinski, Jerzy; Lysko, Jan M.; Koszur, Jan; Brzozka, Zbigniew; Malinowska, Elzbieta

2001-08-01

232

Absorption and fluorescence studies on interaction between cationic dyes and Klebsiella K7 capsular polysaccharide.  

PubMed

Interaction of cationic dyes, pinacyanol chloride, acridine orange and phenosafranin, with Klebsiella K7 capsular polysaccharide has been investigated by spectrophotometric and spectrofluorometric measurements. The acidic polysaccharide induce a metachromatic blue shift of the absorption band of pinacyanol chloride from 600 nm to 495 nm, indicating strong metachromasy. Stoichiometry of polyanion and dye cation (1:1.5) in the polymer-dye compound formed by the interaction between pinacyanol chloride dye and K7 polymer indicate that both glucuronic acid and pyruvic acid act as the potential anionic sites for interaction. Both spectrophotometric titration of pinacyanol chloride and spectrofluorometric titration of acridine orange and phenosafranin dyes by the polymer gave quite comparable equivalent weights for the polymer. Dye-polymer interaction studies indicated induction of metachromasy in the cationic dye by the anionic biopolymer, establishing its chromotropic character. PMID:1512016

Mitra, A; Chakraborty, A K

1992-06-01

233

Cross-Reactivity of Toxin and Pathogen Assays on the Light Addressable Potentiometric Sensor.  

National Technical Information Service (NTIS)

This report describes testing using toxin and pathogen immunoligand assays (ILA) with the Light Addressable Potentiometric Sensor (LAPS). The purpose of the work was to determine the scope and magnitude of cross-reactivity interactions of candidate antibo...

D. G. Menking C. R. Johnson S. L. Eure

1993-01-01

234

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.

Ismail, Fatma; Adeloju, Samuel B.

2010-01-01

235

Titrated oxygen requirement and prognostication in idiopathic pulmonary fibrosis  

PubMed Central

Background The supplemental oxygen flow rate is a common bedside measure of gas exchange impairment. We aimed to determine whether a titrated oxygen requirement predicted mortality in idiopathic pulmonary fibrosis. Methods We examined 104 adults with idiopathic pulmonary fibrosis enrolled in a prospective cohort study and a validation cohort of 151 adults with a variety of interstitial lung diseases. The titrated oxygen requirement was defined as the lowest oxygen flow rate required to maintain an oxyhemoglobin saturation of 96% while standing. Cox proportional hazards models and time-dependent receiver operating characteristic curves were used to examine survival time. Results A higher titrated oxygen requirement was associated with a greater mortality rate independent of forced vital capacity and six-minute walk test results in idiopathic pulmonary fibrosis (adjusted hazard ratio per 1 L/min = 1.10, 95% confidence interval 1.01 to 1.20). The titrated oxygen requirement was at least as accurate as pulmonary function and six-minute walk testing at predicting 1-year mortality. Findings were similar in other interstitial lung diseases. Conclusion The titrated oxygen requirement is a simple, inexpensive bedside measurement that aids prognostication in idiopathic pulmonary fibrosis.

Hook, Jaime L.; Arcasoy, Selim M.; Zemmel, David; Bartels, Matthew; Kawut, Steven M.; Lederer, David J.

2011-01-01

236

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

237

Two-phase titration of cerium(III) by permanganate  

SciTech Connect

This paper presents a method for the two-phase titrimetric determination of cerium(III) with permanganate which does not require an expenditure of sugar and preliminary removal of chlorides and nitrates. The interaction of cerium(III) with permanganate at room temperature was studied as a function of the pH, the concentration of pyrophosphate, tetraphenylphosphonium (TPP), permanganate, and extraneous compounds, the rate of titration, and the time of stay of the solution in air before titration. The investigations were conducted according to the following methodology: water, solution of cerium(III) pyrophosphate, and TPP were introduced into an Erlenmeyer flask with a side branch near the bottom for clearer observation of the color of the chloroform phase. The authors established the given pH value, poured the water into a volume of 50 ml, and added chloroform. The result was titrated with permanganate solutions of various concentrations until a violet color appeared in the chloroform phase.

Lazarev, A.I.; Lazareva, V.I.; Gerko, V.V.

1987-02-01

238

Cation binding by bacteriorhodopsin  

SciTech Connect

It was 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 (lambda/sub max/ approx. = 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 approx. = 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.

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

1984-01-01

239

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

240

Potentiometric surface of the Upper Floridan aquifer in the St. Johns River water management district and vicinity, Florida, September 2005  

USGS Publications Warehouse

This map depicts the potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity for September 2005. Potentiometric contours are based on water-level measurements collected at 643 wells during the period September 12-28, near the end of the wet season. Some contours are inferred from previous potentiometric-surface maps with larger well networks. The potentiometric surface of the carbonate Upper Floridan aquifer responds mainly to rainfall, and more locally, to ground-water withdrawals and springflow. Potentiometric-surface highs generally correspond to topographic highs where the aquifer is recharged. Springs and areas of diffuse upward leakage naturally discharge water from the aquifer and are most prevalent along the St. Johns River. Areas of discharge are reflected by depressions in the potentiometric surface. Ground-water withdrawals locally have lowered the potentiometric surface. Ground water in the Upper Floridan aquifer generally flows from potentiometric highs to potentiometric lows in a direction perpendicular to the contours.

Kinnaman, Sandra L.

2006-01-01

241

Potentiometric Surface of the Upper Floridan Aquifer in the St. Johns River Water Management District and Vicinity, Florida, May 2007  

USGS Publications Warehouse

Introduction This map depicts the potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity for May 2007. Potentiometric contours are based on water-level measurements collected at 566 wells during the period May 4-June 11 near the end of the dry season, however most of the water level data for this map were collected by the U.S. Geological Survey during the period May 21-25, 2007. Some contours are inferred from previous potentiometric-surface maps with larger well networks. The potentiometric surface of the carbonate Upper Floridan aquifer responds mainly to rainfall, and more locally, to ground-water withdrawals and spring flow. Potentiometric-surface highs generally correspond to topographic highs where the aquifer is recharged. Springs and areas of diffuse upward leakage naturally discharge water from the aquifer and are most prevalent along the St. Johns River. Areas of discharge are reflected by depressions in the potentiometric surface. Ground-water withdrawals locally have lowered the potentiometric surface. Ground water in the Upper Floridan aquifer generally flows from potentiometric highs to potentiometric lows in a direction perpendicular to the contours.

Kinnaman, Sandra L.; Dixon, Joann F.

2007-01-01

242

Potentiometric Surface of the Upper Floridan Aquifer in the St. Johns River Water Management District and Vicinity, Florida, September 2007  

USGS Publications Warehouse

This map depicts the potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity for September 2007. Potentiometric contours are based on water-level measurements collected at 554 wells during the period September 15-27, near the end of the wet season. Some contours are inferred from previous potentiometric-surface maps with larger well networks. The potentiometric surface of the carbonate Upper Floridan aquifer responds mainly to rainfall, and more locally, to ground-water withdrawals and spring flow. Potentiometric-surface highs generally correspond to topographic highs where the aquifer is recharged. Springs and areas of diffuse upward leakage naturally discharge water from the aquifer and are most prevalent along the St. Johns River. Areas of discharge are reflected by depressions in the potentiometric surface. Ground-water withdrawals locally have lowered the potentiometric surface. Ground water in the Upper Floridan aquifer generally flows from potentiometric highs to potentiometric lows in a direction perpendicular to the contours.

Kinnaman, Sandra L.; Dixon, Joann F.

2008-01-01

243

Cationic lipids for transfection.  

PubMed

Among other strategies, the use of cationic lipids as autoassembling vehicles for non viral DNA transfection has received considerable attention. An exponentially growing litterature has been published on this topic (over 700 hits for the past decade, including 400 in the last two years). The present review focuses on the main present strategies aiming at improving cationic lipids induced transfection, and on some of the frequently encountered problems that should be solved to apply these non-viral vectors for human health. The review contains several sections dealing with the chemistry, physico-chemistry, cell biology, in vivo biology, and targeting of cationic-lipid DNA complexes. PMID:12678798

Nicolazzi, Céline; Garinot, Marie; Mignet, Nathalie; Scherman, Daniel; Bessodes, Michel

2003-07-01

244

Modeling the acid-base properties of bacterial surfaces: A combined spectroscopic and potentiometric study of the gram-positive bacterium Bacillus subtilis.  

PubMed

In this study, macroscopic and spectroscopic data were combined to develop a surface complexation model that describes the acid-base properties of Bacillus subtilis. The bacteria were freeze-dried and then resuspended in 0.1 M NaCl ionic medium. Macroscopic measurements included potentiometric acid-base titrations and electrophoretic mobility measurements. In addition, ATR-FTIR spectra of wet pastes from suspensions of Bacillus subtilis at different pH values were collected. The least-squares program MAGPIE was used to generate a surface complexation model that takes into account the presence of three acid-base sites on the surface: tripple bond COOH, tripple bond NH+, and tripple bond PO-, which were identified previously by XPS measurements. Both potentiometric titration data and ATR-FTIR spectra were used quantitatively, and electrostatic effects at the charged bacterial surface were accounted for using the constant capacitance model. The model was calculated using two different approaches: in the first one XPS data were used to constrain the ratio of the total concentrations of all three surface sites. The capacitance of the double layer, the total buffer capacity, and the deprotonation constants of the tripple bond NH+, tripple bond POH, and tripple bond COOH species were determined in the fit. A second approach is presented in which the ratio determined by XPS of the total concentrations of tripple bond NH+ to tripple bond PO- sites is relaxed. The total concentration of tripple bond PO- sites was determined in the fit, while the deprotonation constant for tripple bond POH was manually varied until the minimization led to a model which predicted an isoelectric point that resulted in consistency with electrophoretic mobility data. The model explains well the buffering capacity of Bacillus subtilis suspensions in a wide pH range (between pH=3 and pH=9) which is of considerable environmental interest. In particular, a similar quantitative use of the IR data opens up possibilities to model other bacterial surfaces at the laboratory scale and help estimate the buffering capacity of carboxylate-containing compounds in natural samples. PMID:17948795

Leone, Laura; Ferri, Diego; Manfredi, Carla; Persson, Per; Shchukarev, Andrei; Sjöberg, Staffan; Loring, John

2007-09-15

245

New chemical titration proposed for potassium mud testing  

Microsoft Academic Search

An accurate and easy-to-use procedure for measuring the potassium ion concentration in drilling and completion fluids has been developed and successfully used in Union Oil Co. of California's drilling operations. This volumetric analysis is based on the quantitative conversion of soluble sodium tetraphenylboron to the insoluble potassium tetraphenylboron and back titration with a quaternary ammonium salt in the presence of

Zilch

1984-01-01

246

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

247

Treatment of breakthrough cancer pain: to titrate or to proportionate?  

PubMed

Abstract Breakthrough cancer pain can be treated effectively by rapid-onset opioids, such as sublingual fentanyl. However, it remained unclear how the optimal dose of sublingual fentanyl should be determined. Dosing proportional to basic opioid regimen is now proposed as an alternative to dose titration. PMID:23971682

Hans, Guy H

2013-09-05

248

Titrating-Delay Matching-to-Sample in the Pigeon  

PubMed Central

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 incorrect matches decrease the delay, and steady-state titrated delays serve as the primary dependent measure. The present series of experiments investigated the effects of several procedural variables on performance in TDMTS procedures in an effort to elucidate better its features to allow for more precision in future use. Experiment 1 reports results from a parametric analysis of fixed-ratio response requirements on the sample key that indicated improved remembering in the form of higher daily titrated delay values as the requirement was increased. Experiment 2 investigated the extent to which the initial delay value in each session affected session-wide delay values. Results indicated that regardless of value of the initial delay, the subjects' performances adjusted the delay values in the direction of the known baseline delay-value levels. Experiment 3 manipulated the step size by which delay values were adjusted and the results indicated that larger step sizes increased both session-to-session variability and within-session range of titrated delay values, although the average values remained approximately the same. These results suggest that the TDMTS task serves as a promising procedure to study what many refer to as memory.

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

2010-01-01

249

Macromolecular Effects on the Titration Curves of Parotid Gland Fluid.  

National Technical Information Service (NTIS)

Macromolecules were found to act as additives to the total buffering action in parotid saliva. This additive effect was related to the proteins in the gland fluid, and could be demonstrated by analyzing changes in the end-point segments of titration curve...

K. C. Hoerman G. E. Clark A. Y. Balekjian

1968-01-01

250

Mapping glycoside hydrolase substrate subsites by isothermal titration calorimetry  

Microsoft Academic Search

Relating thermodynamic parameters to structural and biochemical data allows a better understanding of substrate binding and its contribution to catalysis. The analysis of the binding of carbohydrates to proteins or enzymes is a special challenge because of the multiple interactions and forces involved. Isothermal titration calorimetry (ITC) provides a direct measure of binding enthalpy (Ha) and allows the determination of

Gennady Zolotnitsky; Uri Cogan; Noam Adir; Vered Solomon; Gil Shoham; Yuval Shoham

2004-01-01

251

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…

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

2006-01-01

252

A Low-Cost Device for Automatic Photometric Titrations  

NASA Astrophysics Data System (ADS)

Electronics is an important topic in chemistry courses. However, the introduction of basic concepts is often difficult and the lab instruments are frequently seen as "black boxes". To address this problem, we propose the construction of a simple, low-cost (about $150 U.S.) automatic photometric titrator employing a light-emitting diode (LED) and a phototransistor. The electronic circuit can be assembled by the students themselves. The device was employed to implement a common procedure in chemical labs, making feasible the introduction of concepts related to electronics in undergraduate chemistry courses. The titrator is able to work automatically, since a feedback system permits stopping the addition of titrant solution when the end-point is achieved. With this demonstration, it can be stressed that automatic procedures can be implemented without expensive instruments. Additionally, a classical procedure becomes more attractive to the students and its importance to chemical analysis can be emphasized. The feasibility of the titrator was demonstrated by acid-base titrations of HCl solutions with NaOH in the presence of phenolphthalein and by iodimetric determination of ascorbic acid in vitamin C tablets and lemon juice. Precise results (0.7% relative standard deviation, n = 10) in agreement at the 95% confidence level with those attained by a conventional procedure were obtained.

Rocha, Fábio R. P.; Reis, Boaventura F.

2000-02-01

253

Isothermal Titration Calorimeter For Research And Education (DURIP-10).  

National Technical Information Service (NTIS)

We have purchased a state-of-the-art MicroCal Auto-iTC200 Isothermal Titration Calorimetry (ITC) System. ITC is the gold standard for measuring biomolecular interactions. ITC simultaneously determines all binding parameters in a single experiment which is...

2011-01-01

254

Sorption and desorption of quaternary amine cations on clays  

SciTech Connect

The authors have studied the sorption and desorption of three quaternary amines, namely, nonyltrimethylammonium, dodecyltrimethylammonium, and hexadecyltrimethylammonium, on homoionic Na- and K-montmorillonite using a titration procedure. More than 99% of all three of the quaternary amine cations studied were sorbed on the montmorillonite when the added amines were less than 70% of the cation-exchange capacity of the montmorillonite. Sorption of quaternary amine cations involves at least two types of reactions, namely, an exchange reaction and the adsorption of amines at nonexchangeable sites. The exchange reaction proceeded almost to completion when Na[sup +] was the exchangeable cation. Exchangeable K[sup +] was much more difficult to replace. The adsorbed quaternary amine cations were not easily desorbed in the presence of 0.1 M NaCl and KCl solutions. In addition, desorption of quaternary amines did not increase with prolonged equilibrium time, up to 180 days. Therefore, it appears that there is good promise in using quaternary amine-modified clays as effective sorbents for removing organic pollutants or mitigating their mobilities in the environment. 26 refs., 5 figs., 6 tabs.

Zhang, Z.Z.; Sparks, D.L. (Univ. of Delaware, Newark, DE (United States)); Scrivner, N.C. (DuPont Engineering, Newark, DE (United States))

1993-08-01

255

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.

2013-01-01

256

New potentiometric sensors based on selective recognition sites for determination of ephedrine in some pharmaceuticals and biological fluids.  

PubMed

New cost-effective potentiometric membrane sensors with cylindrical configuration responsive to ephedrine are described. The sensors setup is, based on the use of triacetyl-?-cyclodextrin [(triacetyl-?-CD)] as a neutral ionophore embedded in a plasticized poly (vinyl chloride) (PVC) matrix (sensor I) and carboxylated poly(vinyl chloride) [(PVC-COOH)] as a simultaneous plastic matrix and ion exchanger (sensor II). Both sensors showed significant enhancement of response towards ephedrinium cation (EPD(+)) over a concentration range of 3.0 × 10(-5)-8.0 × 10(-3) mol L(-1) at pH 4-9 and 3-8 with low detection limits of 5.7 × 10(-6) and 6.2 × 10(-6) mol L(-1) for sensors (I) and (II), respectively. The sensors displayed near-Nernstian cationic slope of 57.0 and 55.6 mV decade(-1) for EPD(+) and the effects of lipophilic salts and various foreign common ions were examined. The sensors were also satisfactorily used as tubular detectors in a double channel flow injection system. The intrinsic characteristics of the detectors in a low dispersion manifold under hydrodynamic mode of operation were determined and compared with data obtained under batch mode of operation. Validation of the method revealed good performance characteristics including long life span, good selectivity for EPD(+) over a wide variety of other organic compounds, long term stability, high reproducibility, fast response, low detection limit, wide measurement range, acceptable accuracy and precision. Applications of the sensors to the determination of EPD(+) in pharmaceutical formulations and spiked biological fluid samples were carried out and compared with standard techniques. Notably, the sensors introduced offer several advantages over many of those previously described that are amenable to quality control/quality assurance assessment of the homogeneity, stability and purity of ephedrine drug tablets. PMID:23200395

Hassan, Saad S M; Kamel, Ayman H; Abd El-Naby, Heba

2012-11-02

257

Electrochemical Sample Matrix Elimination for Trace Level Potentiometric Detection with Polymeric Membrane Ion-Selective Electrodes  

PubMed Central

Potentiometric sensors are today sufficiently well understood and optimized to reach ultra-trace level (sub-nanomolar) detection limits for numerous ions. In many cases of practical relevance, however, a high electrolyte background hampers the attainable detection limits. A particularly difficult sample matrix for potentiometric detection is seawater, where the high saline concentration forms a major interfering background and reduces the activity of most trace metals by complexation. This paper describes for the first time a hyphenated system for the online electrochemically modulated preconcentration and matrix elimination (EMPM) of trace metals, combined with a downstream potentiometric detection with solid contact polymeric membrane ion-selective microelectrodes. Following the preconcentration at the bismuth coated electrodes, the deposited metals are oxidized and released to a medium favorable to potentiometric detection, in this case calcium nitrate. Matrix interferences arising from the saline sample medium are thus circumvented. This concept is successfully evaluated with cadmium as a model trace element and offers potentiometric detection down to low parts per billion levels in samples containing 0.5 M NaCl background electrolyte.

Chumbimuni-Torres, Karin Y.; Calvo-Marzal, Percy; Wang, Joseph; Bakker, Eric

2008-01-01

258

Potentiometric map of the Winona-Tallahatta Aquifer in northwestern Mississippi, fall 1979  

USGS Publications Warehouse

The potentiometric map of the Winona-Tallahatta aquifer is one of 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 Winona-Tallahatta aquifer the potentiometric surface is strongly affected by recharge from precipitation, by topography, and by drainage of the aquifer by streams. The potentiometric surface slopes downward generally to the west away from the area of outcrop and is strongly affected by recharge from precipitation, by topography, and by drainage of the aquifer by streams. The potentiometric surface slopes downward generally to the west away from the area of outcrop and is strongly affected by pumpage from wells in Leflore, Sunflower , and Bolivar Counties, Historically, water levels in or near the outcrop of the Winona-Tallahatta have shown little or no long-term changes, but the heavy withdrawals in the confined part of the aquifer have caused long-term water-level declines of 1 to 2 feet per year. (USGS)

Wasson, B. E.

1980-01-01

259

Plutonium estimation in the process solutions and oxide dissolved audit samplers by potentiometry using memo titrator.  

National Technical Information Service (NTIS)

Potentiometric method is employed by using memotitrator coupled with combined electrode for the estimation of plutonium. The estimations are carried out on the process samples and the acid dissolved samples for auditing, in the concentration range of 5 g/...

K. Kumaraguru Y. D. Shukla K. Vijayan N. Ramamoorthy U. Jambunathan

1990-01-01

260

Flow injection potentiometric determination of bismuth(III) in anti-acid formulations.  

PubMed

A flow injection potentiometric procedure is proposed for determining bismuth(III) in anti-acid formulations. In this work, a tubular electrode coated with an ion-pair formed between [Bi(EDTA)](-) and tricaprylylmethylammonium cation (Aliquat 336) in a poly(vinylchloride) (PVC) was constructed and used in a single channel flow injection system. The effect of membrane composition, pH and flow injection parameter over the Bi(III) tubular electrode response (slope (mV/decade)) was initially evaluated in quintuplicate in 0.5 mol l(-1) EDTA solution as carrier. The best response (-59.6+/-0.9 mV/decade) was attained with the 5% m/m ion-pair; 65% m/m o-nitrophenyl octyl ether (o-NPOE) and 30% m/m PVC in pH 6-9. The electrode showed a linear response to E (mV) versus log [Bi(EDTA)](-) in the bismuth(III) concentration range from 2.0x10(-5) to 1.0x10(-2) mol l(-1) and a useful lifetime of at least 5 months (more than 1000 determinations for each polymeric membrane). The detection limit was 1.2x10(-5) mol l(-1) and the R.S.D. was less than 2.0% for a solution containing 5.0x10(-4) mol l(-1) bismuth(III) (n=10). Several species such as Cd(II), Mn(II), Ni(II), Zn(II), Co(II), Cu(II), Mg(II), Cr(III) and Al(III) at 1.0x10(-3) mol l(-1) concentration in 0.5 mol l(-1) EDTA solution did not cause any interference. The frequency rate was 90 determinations per hour and the results obtained for bismuth(III) in anti-acid formulations using this flow procedure and those obtained using a spectrophotometric procedure are in agreement at the 95% confidence level. PMID:11397573

Teixeira, M F; Fatibello-Filho, O

2001-06-19

261

Potentiometric Surface of the Upper Floridan Aquifer in the St. Johns River Water Management District and Vicinity, Florida, September 2006  

USGS Publications Warehouse

Introduction This map depicts the potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity for September 2006. Potentiometric contours are based on water-level measurements collected at 571 wells during the period September 11-29, near the end of the wet season. Some contours are inferred from previouspotentiometric-surface maps with larger well networks. The potentiometric surface of the carbonate Upper Floridan aquifer responds mainly to rainfall, and more locally, to ground-water withdrawals and spring flow. Potentiometric-surface highs generally correspond to topographic highs where the aquifer is recharged. Springs and areas of diffuse upward leakage naturally discharge water from the aquifer and are most prevalent along the St. Johns River. Areas of discharge are reflected by depressions in the potentiometric surface. Ground-water withdrawals locally have lowered the potentiometric surface. Ground water in the Upper Floridan aquifer generally flows from potentiometric highs to potentiometric lows in a direction perpendicular to the contours.

Kinnaman, Sandra L.; Dixon, Joann F.

2007-01-01

262

An estimated potentiometric surface of the Death Valley region, Nevada and California, developed using geographic information system and automated interpolation techniques  

Microsoft Academic Search

An estimated potentiometric surface was constructed for the Death Valley region, Nevada and California, from numerous, disparate data sets. The potentiometric surface was required for conceptualization of the ground-water flow system and for construction of a numerical model to aid in the regional characterization for the Yucca Mountain repository. Because accurate, manual extrapolation of potentiometric levels over large distances is

C. C. Faunt; A. K. Turner

1998-01-01

263

A neutral carrier-based liquid membrane microelectrode for divalent putrescine cations  

Microsoft Academic Search

A new ion-selective liquid membrane microelectrode, based on the neutral carrier 1,1?-bis(2,3-naphtho-18-crown-6), is described\\u000a that shows the dependence of EMF on the activity of divalent putrescine cations a\\u000a Put, with the linear slope s\\u000a Put?=?26?±?3?mV\\/decade (mean?±?SD, N?=?18), in the range 10?4–10?1?M at 25?±?1?°C. Values of potentiometric putrescine cation selectivity coefficients of logK\\u000a Pot\\u000a Put\\u000a \\u000a j\\u000a (mean?±?SD, N) are obtained by

Herbert R. L. Drouin

1999-01-01

264

Tattoo-based potentiometric ion-selective sensors for epidermal pH monitoring.  

PubMed

This article presents the fabrication and characterization of novel tattoo-based solid-contact ion-selective electrodes (ISEs) for non-invasive potentiometric monitoring of epidermal pH levels. The new fabrication approach combines commercially available temporary transfer tattoo paper with conventional screen printing and solid-contact polymer ISE methodologies. The resulting tattoo-based potentiometric sensors exhibit rapid and sensitive response to a wide range of pH changes with no carry-over effects. Furthermore, the tattoo ISE sensors endure repetitive mechanical deformation, which is a key requirement of wearable and epidermal sensors. The flexible and conformal nature of the tattoo sensors enable them to be mounted on nearly any exposed skin surface for real-time pH monitoring of the human perspiration, as illustrated from the response during a strenuous physical activity. The resulting tattoo-based ISE sensors offer considerable promise as wearable potentiometric sensors suitable for diverse applications. PMID:23113321

Bandodkar, Amay J; Hung, Vinci W S; Jia, Wenzhao; Valdés-Ramírez, Gabriela; Windmiller, Joshua R; Martinez, Alexandra G; Ramírez, Julian; Chan, Garrett; Kerman, Kagan; Wang, Joseph

2012-10-31

265

APPLICATION OF CHEMICAL MODIFIED ELECTRODE IN COULOMETRIC TITRATION FOR DETERMINATION OF SOLANESOL  

Microsoft Academic Search

The problem of large deviation of determination of solanesol by coulometric titration when using direct titration technique and double Pt electrodes amperometric method indicating the end-point has been resolved. In titration process, solanesol, an electroinactive species, can be adsorbed on the surfaces of Pt electrodes and inhibit electrode reactions of Br and Br2. Therefore, when titration reaches the end-point, the

Ge Zhao; Jianying Qu; Meng Liu; Kuaizhi Liu; Zuliang Du

2002-01-01

266

Complexation thermodynamics of some alkali-metal cations with 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane in Acetonitrile  

Microsoft Academic Search

The interaction of 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (Kryptofix5) with alkali-metal cations (Li+, Na+, K+) in aprotic medium (acetonitrile) has been investigated. Conductance measurements demonstrated that 1:1 metal cation:ligand\\u000a stoichiometries are found with these cations in this solvent. 7Li and 23Na NMR experiments were carried out by titration of the metal cation solutions with Kryptofix5 solution in CD3CN + CH3CN at 298 K. Thermodynamic parameters of complexation

Mohammad Kazem Rofouei; Asieh Ahmadalinezhad; Mehdi Taghdiri

2007-01-01

267

Solubility of TTCP and ?-TCP by solid titration  

Microsoft Academic Search

ObjectiveUsing solid titration with hydroxyapatite (HAp) and octacalcium phosphate, HAp has been found to be more stable than dicalcium phosphate dihydrate (DCPD) even at lower pH, inconsistent with the widely reported view that DCPD is less soluble than other calcium phosphates below pH 4.2. A check of the behaviour of other calcium phosphates (TTCP; Ca\\/P: 2.00 and ?-TCP; Ca\\/P: 1.33)

H.-B. Pan; B. W. Darvell

2009-01-01

268

Automatic karl fischer titration of moisture in sunflower seed  

Microsoft Academic Search

An automatic Karl Fischer (KF) titrator of the motor-driven buret type was applied to the determination of moisture in sunflower\\u000a seed. A study of the effect of sample size on KF moisture analysis showed a significant decrease in moisture content with\\u000a increase in sample size from 1 to 5 g. In the moisture range of 5.5–10.5%, a sample size of

James A. Robertson; W. R. Windham

1983-01-01

269

Solubility of dicalcium phosphate dihydrate by solid titration.  

PubMed

Solid-titration results for hydroxyapatite (HAp), octacalcium phosphate, beta-tricalcium phosphate and tetracalcium phosphate have shown that the only stable phase in 100 mmol x l(-1) KCl at 37 degrees C is HAp. In particular, dicalcium phosphate dihydrate (DCPD) did not form at pH <4.2 (where it is otherwise believed to be stable) except as a metastable phase under conditions of slight supersaturation. The behaviour of DCPD itself under the same conditions requires checking. Solid titration was used to determine the apparent solubility of DCPD in a 100-mmol x l(-1) KCl solution at 37.0 +/- 0.1 degrees C over the pH range 3.2-11.6. The constitution of the precipitate was determined by X-ray diffraction, particle morphology was observed by scanning and transmission electron microscopy, and the precipitate Ca/P ratio was calculated by energy-dispersive X-ray analysis. The titration curve for DCPD was substantially lower than the position reported elsewhere. DCPD was the only identified phase at equilibrium at pH 3.60 and 4.50, but HAp was formed after seeding with 1 mg HAp at DCPD equilibrium at pH 4.47, 3.60 and 3.30. It is concluded that the titration curve observed for DCPD corresponds to the solubility isotherm for the phase, but that this represents a metastable equilibrium. HAp is more stable than DCPD, particularly below pH 4.2. The implications for calcium phosphate studies are profound as the reverse is generally believed to be true. Thus, solubility results and the nature of the carious lesion need reconsideration. PMID:19439946

Pan, H-B; Darvell, B W

2009-05-08

270

Titration of long-chain quaternary ammonium compounds using tetraphenylboron  

Microsoft Academic Search

A rapid macro procedure for the determination of long-chain quaternary ammonium compounds (QAC) has been developed using sodium\\u000a tetraphenylboron as a titrant. About 1–1.5 meq of QAC is dissolved or dispersed in 50 ml of water. Dichlorofluorescein is\\u000a added as an indicator. The sample is then titrated with 0.06 N aqueous sodium tetraphenylboron. As long as free QAC is present

L. D. Metcalfe; R. J. Martin; A. A. Schmitz

1966-01-01

271

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

272

Fentanyl buccal tablet for breakthrough cancer pain: why titrate?  

PubMed

Breakthrough cancer pain is a significant problem for many patients with cancer because of the fast onset and often unpredictable nature of the pain episodes. The rapid onset opioids therefore have a central role to play in the management of breakthrough cancer pain. The rapid onset opioid fentanyl buccal tablet provides a fast analgesic effect and is easy to administer. However, titration of the medication is essential in order to optimize the management of pain. This is because individual patient characteristics, comorbidities, and other treatments may influence the absorption, pharmacokinetics, and pharmacodynamics of drugs. It is therefore important to individualize treatment by determining the effective dose for each patient, which is the dose that provides adequate analgesia and minimizes undesirable adverse effects. Data from clinical studies of fentanyl buccal tablet show that patients' effective doses ranged from 100 to 800 µg per episode, highlighting the need for the titration process. Following successful dose titration, treatment with fentanyl buccal tablet can achieve significant pain relief as early as 10 minutes after administration, resulting in a high level of patient satisfaction. PMID:20807349

Kleeberg, Ulrich R; Filbet, Marilène; Zeppetella, Giovambattista

2010-08-27

273

The Acid-Base Titration of a Very Weak Acid: Boric Acid  

ERIC Educational Resources Information Center

|A laboratory experiment based on the titration of boric acid with strong base in the presence of d-mannitol is described. Boric acid is a very weak acid and direct titration with NaOH is not possible. An auxiliary reagent that contributes to the release of protons in a known stoichiometry facilitates the acid-base titration. Students obtain the…

Celeste, M.; Azevedo, C.; Cavaleiro, Ana M. V.

2012-01-01

274

Titration of strong and weak acids by sequential injection analysis technique  

Microsoft Academic Search

A sequential injection analysis (SIA) titration method has been developed for acid-base titrations. Strong and weak acids in different concentration ranges have been titrated with a strong base. The method is based on sequential aspiration of an acidic sample zone and only one zone of the base into a carrier stream of distilled water. On their way to the detector,

Silla Maskula; Johan Nyman; Ari Ivaska

2000-01-01

275

Biosensors based on light-addressable potentiometric sensors for urea, penicillin and glucose  

Microsoft Academic Search

Novel potentiometric biosensors based on light-addressable potentiometric sensors for detection of glucose, penicillin and urea as model compounds are described. n-type silicon substrates covered with SiO2 and\\/or Al2O3 were applied as a pH sensor. The Al2O3 and SiO2 films were pH-sensitive in the range pH 3–11. The pH-sensitive electrode was applied to produce biosensors for glucose, penicillin and urea by

Atsushi Seki; Syuu-ichi Ikeda; Izumi Kubo; Isao Karube

1998-01-01

276

The light-addressable potentiometric sensor for multi-ion sensing and imaging.  

PubMed

The light-addressable potentiometric sensor (LAPS) is a semiconductor-based chemical sensor with an electrolyte-insulator-semiconductor structure. The LAPS can have many measuring points integrated on the sensing surface, which are individually accessed by a light beam. By modifying the measuring points with different materials, a single sensor plate can be used as a multi-analyte sensor. In this paper, instrumentation and application of LAPS to multi-ion sensing and imaging are described. As a new application of LAPS, potentiometric imaging of a microfluidic channel is proposed. PMID:16199169

Yoshinobu, T; Iwasaki, H; Ui, Y; Furuichi, K; Ermolenko, Yu; Mourzina, Yu; Wagner, T; Näther, N; Schöning, M J

2005-09-30

277

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

SciTech Connect

This report details a geostatistical analysis of potentiometric data from the Wolfcamp 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 Wolfcamp 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.

Harper, W.V.; Furr, J.M.

1986-04-01

278

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.

Szigeti, Zsofia; Malon, Adam; Vigassy, Tamas; Csokai, Viktor; Grun, Alajos; Wygladacz, Katarzyna; Ye, Nan; Xu, Chao; Chebny, Vincent J.; Bitter, Istvan; Rathore, Rajendra; Bakker, Eric; Pretsch, Erno

2010-01-01

279

A mercury(II) selective sensor based on N,N'-bis(salicylaldehyde)-phenylenediamine as neutral carrier for potentiometric analysis in water samples.  

PubMed

Mercuric ions in water samples were determined by a new modified carbon paste electrode based on N,N'-bis(salicylaldehyde)-phenylenediamine (salophen) as a chemical modifier. The construction, performance, and applications of mercury carbon paste electrode are described. The electrode displays a linear log[Hg(2+)] versus EMF response over a wide concentration range of 3.2 x 10(-7) to 3.2 x 10(-4) with Nernstian slope of 58.8+/-0.3 mV/decade with limit of detection 1.5 x 10(-7) over the pH range 3.8-7.8; the presence of the complex Hg(OH)(+) ion explains the slope of the response curve. The proposed sensor shows a reasonable discrimination ability towards Hg(II) in comparison to some alkali, alkaline earth transition and heavy metal ions. The modified electrode was applied as indicator electrode in potentiometric titration and successfully used to determine mercury(II) in water samples with satisfactory results. PMID:19195781

Abu-Shawish, Hazem M

2009-01-16

280

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

281

Spectrophotometric and spectrofluorometric studies on interaction of cationic dyes with bacterial capsular polysaccharide.  

PubMed

Interaction of Klebsiella K14 capsular polysaccharide with cationic dyes pinacyanol chloride, acridine orange and phenosafranin has been studied by spectrophotometric and spectrofluorometric techniques. The polymer containing both glucuronic acid and pyruvic acid in its repeating unit behaved as a unique polyelectrolyte. It induced blue shift of the absorption band of pinacyanol chloride indicating strong metachromasy. Stoichiometry of the polyanion and the dye cations in the polymer-dye compound (1:2) indicated that both glucuronic acid and pyruvic acid acted as potential anionic sites for interaction with the cationic dye molecules. The stoichiometry of anionic site (of polyanion): cationic site (of dye) in the polymer dye compound was calculated as 1:1. Interaction of the polymer with acridine orange and phenosafranin dyes studied by fluorescence measurements demonstrated Stern-Volmer type of quenching. Equivalent weight of the polymer was determined by spectrophotometric and spectrofluorometric titrations. From the present studies chromotropic property of the polymer was established. PMID:9854905

Mitra, A; Chakraborty, A K

1998-08-01

282

A test method for analyzing anionic or cationic surfactants in industrial water  

Microsoft Academic Search

A general 2-phase titration method is introduced for the quantitative identification of either anionic or cationic surface\\u000a active agents commonly used in the domestic and industrial applications. Initially, an appropriate amount of quaternary ammonium\\u000a compound is added to an unknown water sample to be analyzed and to ensure the treated sample contains excess amount of quaternary\\u000a ammonium compound, and thus,

L. K. Wang

1975-01-01

283

Evidence for antiferromagnetic order in BiâSrâCuOâ phase with stoichiometric cation composition  

Microsoft Academic Search

We have succeeded in synthesizing the insulating phase of BiâSrâCuO{sub 6+δ} (Bi2201) with the stoichiometric cation composition by use of a heat treatment technique in an evacuated tube with titanium powders. The excess oxygen content δ and the average valence of Bi were determined electrochemically by the coulometric titration method. The value of δ in the insulating phase was found

Masaki Kato; Kazuyoshi Yoshimura; Koji Kosuge

1997-01-01

284

Channel permeant cations compete selectively with noncompetitive inhibitors of the nicotinic acetylcholine receptor.  

PubMed

Previous work suggests that noncompetitive inhibitor (NCI) ligands and channel permeant cations bind to sites within the nicotinic acetylcholine receptor ion channel. We have used ethidium as a fluorescent probe of the NCI site to investigate interactions between NCI ligands and channel permeant cations. We found that ethidium can be completely displaced from the receptor by a variety of inorganic monovalent and divalent cations. The rank order of monovalent cation affinities was found to be Tl+ greater than Rb+ greater than or equal to K+ greater than Cs+ greater than Na+ greater than Li+. The monovalent cation Kd values vary markedly over a 40-fold range, from 3 to 121 mM. The Kd values and rank order correspond to values determined previously from electrophysiological data. Hill plots of the back titrations yield slopes of 1.0 for all monovalent cations, indicating a single class of independent sites, as shown previously for NCI ligands. Scatchard analysis of ethidium binding in the presence of Tl+ reveals a reduction in affinity and no changes in the maximal number of sites. In the presence of agonist the kinetics of ethidium dissociation induced by the addition of phencyclidine or cations alone or the simultaneous addition of both are nearly identical. The ethidium dissociation rate induced by either phencyclidine or cations is regulated by the occupation of the agonist sites in a similar manner. These results indicate that the effect of cations on NCI ligand binding occurs by mutually exclusive competition. We suggest that NCIs can regulate cation binding at a physiological cation recognition site that is likely part of the cation permeation path through the receptor channel. PMID:1715868

Herz, J M; Kolb, S J; Erlinger, T; Schmid, E

1991-09-01

285

Functional Role and Affinity of Inorganic Cations in Stabilizing the Tetrameric Structure of the KcsA K+ Channel  

PubMed Central

Crystal structures of the tetrameric KcsA K+ channel reveal seven distinct binding sites for K+ ions within the central pore formed at the fourfold rotational symmetry axis. Coordination of an individual K+ ion by eight protein oxygen atoms within the selectivity filter suggests that ion-subunit bridging by cation–oxygen interactions contributes to structural stability of the tetramer. To test this hypothesis, we examined the effect of inorganic cations on the temperature dependence of the KcsA tetramer as monitored by SDS-PAGE. Inorganic cations known to permeate or strongly block K+ channels (K+, Rb+, Cs+, Tl+, NH4+, Ba2+, and Sr2+) confer tetramer stability at higher temperatures (T0.5 range = 87°C to >99°C) than impermeant cations and weak blockers (Li+, Na+, Tris+, choline+; T0.5 range = 59°C to 77°C). Titration of K+, Ba2+, and other stabilizing cations protects against rapid loss of KcsA tetramer observed in 100 mM choline Cl at 90°C. Tetramer protection titrations of K+, Rb+, Cs+, Tl+, and NH4+ at 85°C or 90°C exhibit apparent Hill coefficients (N) ranging from 1.7 to 3.3 and affinity constants (K0.5) ranging from 1.1 to 9.6 mM. Ba2+ and Sr2+ titrations exhibit apparent one-site behavior (N ? 1) with K0.5 values of 210 nM and 11 ?M, respectively. At 95°C in the presence of 5 mM K+, titration of Li+ or Na+ destabilizes the tetramer with K0.5 values of 57 mM and 109 mM, respectively. We conclude that specific binding interactions of inorganic cations with the selectivity filter are an important determinant of tetramer stability of KscA.

Krishnan, Manoj N.; Bingham, Jon-Paul; Lee, Siew Hwee; Trombley, Patrick; Moczydlowski, Edward

2005-01-01

286

Condensation of nucleic acids by intercalating aromatic cations.  

PubMed

Certain intercalating aromatic cations, such as the fluorochrome acridine orange or the antitumor drug Mitoxantrone, induce condensation of nucleic acids in solutions. The appearance of the condensed form during titration of nucleic acids with these intercalating ligands can be quantitatively monitored by light scatter measurements. The resulting highly reproducible light scatter transition curves are typical of the cooperative processes, and the transitions occur at different critical concentrations of the ligands depending upon both the ligand itself and the primary structure (base and sugar composition) and the secondary structure (single- or double-stranded) of the nucleic acids. The mechanism of condensation of nucleic acids by intercalating cationic ligands is discussed in light of the model of interactions occurring between certain intercalators and single-stranded nucleic acids and compared with the condensation induced by polyvalent "simple" cations such as Co3+ or spermine4+. The described phenomenon can have an application in analytical and preparative biochemistry for characterization of the primary and secondary structure of nucleic acids and for separation of the compounds. The possibility that the condensation plays a role in mutagenic and pharmacological effects of aromatic cations is considered. PMID:6209715

Kapuscinski, J; Darzynkiewicz, Z

1984-12-01

287

Simple Modification of Karl-Fischer Titration Method for Determination of Water Content in Colored Samples  

PubMed Central

The most commonly used technique for water content determination is Karl-Fischer titration with electrometric detection, requiring specialized equipment. When appropriate equipment is not available, the method can be performed through visual detection of a titration endpoint, which does not enable an analysis of colored samples. Here, we developed a method with spectrophotometric detection of a titration endpoint, appropriate for moisture determination of colored samples. The reaction takes place in a sealed 4?ml cuvette. Detection is performed at 520?nm. Titration endpoint is determined from the graph of absorbance plotted against titration volume. The method has appropriate reproducibility (RSD = 4.3%), accuracy, and linearity (R2 = 0.997).

Tavcar, Eva; Turk, Erika; Kreft, Samo

2012-01-01

288

The Study on Bionic Olfactory Neurochip Based on Light-addressable Potentiometric Sensor  

Microsoft Academic Search

Olfactory system can distinguish thousands of odors. In order to utilize biological olfactory neurons as sensitive material of electronic nose, this article reports an olfactory neurochip as real bionic technique for odorants detection. Effective cultures of olfactory receptor neurons and olfactory bulb cells on the chip have been achieved. Using light-addressable potentiometric sensor (LAPS) as sensing chip to monitor extracellular

Qingjun Liu; Ying Xu; Hua Cai; Lifeng Qin; Xuesong Ye; Rong Li; Ping Wang

2005-01-01

289

Immunoassay of Mouse Immunoglobulin G by a Light-Addressable Potentiometric Sensor.  

National Technical Information Service (NTIS)

A sensitive enzyme immunoassay for the quantitation of mouse immunoglobulin G (mIgG) was developed using a light-addressable potentiometric (LAP) sensor as the detection system. The assay was carried out on nitrocellulose membrane filters and used sandwic...

H. G. Thompson W. E. Lee

1991-01-01

290

Differential Setup of Light-Addressable Potentiometric Sensor with an Enzyme Reactor in a Flow Channel  

Microsoft Academic Search

The light-addressable potentiometric sensor (LAPS) was combined with an enzyme reactor in a fluidic channel. The fluidic channel was mounted on the sensor plate and the enzyme reactor was connected to the fluidic channel. The enzyme reactor was filled with glass beads as enzyme carrier modified by urease which catalyzed production of ammonia depending on the concentration of urea. Double-channel

Ko-ichiro Miyamoto; Midori Yoshida; Taito Sakai; Atsushi Matsuzaka; Torsten Wagner; Shin'ichiro Kanoh; Tatsuo Yoshinobu; Michael J. Schöning

2011-01-01

291

Lateral resolution of light-addressable potentiometric sensors: an experimental and theoretical investigation  

Microsoft Academic Search

The surface potential of semiconductor devices in contact with electrolyte solutions is an important part of signal transduction for a variety of bioanalytical devices. Here we have investigated the lateral resolution at which the surface potential may be measured with a semiconductor-based device, a light-addressable potentiometric sensor (LAPS). We have first established an experimental setup where a permanent charge pattern

Wolfgang J. Parak; Ulrich G. Hofmann; Hermann E. Gaub; John C. Owicki

1997-01-01

292

Can the light-addressable potentiometric sensor (LAPS) detect extracellular potentials of cardiac myocytes?  

Microsoft Academic Search

The light-addressable potentiometric sensor (LAPS) measures localized photo-induced currents from a silicon wafer, which are dependent on the local surface potential and on the intensity of the light pointer. In this study the ability of the LAPS to record extracellular potentials of adherent cells was investigated. Time dependent LAPS photocurrent signals that correlated in time with contractions were recorded from

Wolfgang J. Parak; Michael George; Jan Domke; Manfred Radmacher; Jan C. Behrends; Morgan C. Denyer; Hermann E. Gaub

2000-01-01

293

“LAPS Card”—A novel chip card-based light-addressable potentiometric sensor (LAPS)  

Microsoft Academic Search

A novel design of a light-addressable potentiometric sensor (LAPS) for the realisation of an easy exchangeable and modular measurement set-up is presented in this work. The sensor chip for up to 16 independent sensor spots is integrated in a standard plastic card and the appropriate measurement cell allows a selection of different chip cards within seconds. The measurement cell contains

T. Wagner; C. Rao; J. P. Kloock; T. Yoshinobu; R. Otto; M. Keusgen; M. J. Schöning

2006-01-01

294

Investigation of the spatial resolution of the light-addressable potentiometric sensor  

Microsoft Academic Search

The spatial resolution of the light-addressable potentiometric sensor (LAPS) is investigated both theoretically and experimentally. For a theoretical analysis, the diffusion equation for minority charge carriers in the semiconductor was solved. The results suggest that by thinning the semiconductor wafer, the spatial resolution of the LAPS is no longer limited by the bulk minority charge carrier diffusion length. Spatial resolution

M. George; W. J. Parak; I. Gerhardt; W. Moritz; F. Kaesen; H. Geiger; I. Eisele; H. E. Gaub

2000-01-01

295

Light addressable potentiometric sensor array: A new approach for light beam positioning  

Microsoft Academic Search

An analytical system for multicomponent analysis of liquids based on a light addressable potentiometric sensor (LAPS) with an array of ion-sensitive polymer membranes is presented. A developed LAPS device is based on a BESOI wafer which permits easy fabrication of a sensor with thin silicon membrane and enhanced spatial resolution. To generate the photocurrent the backside silicon was illuminated using

Andrey Ipatov; Kirill Zinoviev; Natalia Abramova; Andrei Bratov

2010-01-01

296

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

297

Selectivity characteristics of potentiometric carbon dioxide sensors with various gas membrane materials  

Microsoft Academic Search

The selectivity characteristics of potentiometric carbon dioxide sensors with regard to various organic and inorganic acid interferences have been systematically examined. When used in conjunction with a standard silicone rubber COâ permeable membrane, the sensor displays surprisingly large response to several organic acids having low volatility, e.g., benzoic, cinnamic, and salicylic acids. If the outer membrane is changed to a

R. K. Kobos; S. J. Parks; M. E. Meyerhoff

1982-01-01

298

Geostatistical Analysis of Potentiometric Data in Wolfcamp Aquifer of the Palo Duro Basin, Texas.  

National Technical Information Service (NTIS)

This report details a geostatistical analysis of potentiometric data from the Wolfcamp 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 potenti...

W. V. Harper J. M. Furr

1986-01-01

299

POTENTIOMETRIC RESPONSE AND MECHANISM OF ANIONIC RECOGNITION OF HETEROCALIXARENE-BASED ION SELECTIVE ELECTRODES  

PubMed Central

The ion selective electrode (ISE)-based potentiometric approach is shown to be an effective means of characterizing the anion recognition sites in the molecular receptor calix[2]pyridino[2]pyrrole (CPP). In particular, potentiometric pH-measurements involving the use of experimental PVC-membranes based on CPP revealed the existence of both mono- and diprotonated forms of the receptor under readily accessible conditions. Based on these analyses, apparent surface protonation constants for this heterocalixarene were found to lie between 8.5–8.9 (pKB1) and 3.3–3.8 (pKB2). CPP was found to interact with targeted anionic analytes based on both coulombic and hydrogen bond interactions, as inferred from varying the kinds of ionic sites present within the membrane phase. Potentiometric selectivity studies revealed that CPP preferred “Y-shaped” anions (e.g. acetate, lactate, benzoate) over spherical anions (e.g. fluoride and chloride), fluoride over chloride within the set of spherical anions, and the ortho- isomer over the corresponding meta- and para- isomers in the case of hydroxybenzoate (salicylate and congeners). In the context of this study the advantages of potentiometric determinations of acetylsalicylic acid using optimized PVC-membranes based on CPP relative to more conventional PVC-membrane ISEs based on traditional anion exchanger were also demonstrated.

Shishkanova, T.V.; Sykora, D.; Sessler, J.L.; Kral, V.

2007-01-01

300

Detection of Picogram Quantities of Botulinus Toxin-B Using the Light Addressable Potentiometric Sensor.  

National Technical Information Service (NTIS)

Detection of picogram quantities of Botulinus toxin-B (BoTX), using Protein A purified biotin- and fluorescein-labelled antibodies, is described in this report. All assays were performed on the Light Addressable Potentiometric Sensor. Results indicate a n...

J. P. Chambers J. J. Valdes

1992-01-01

301

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

302

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

303

Potentiometric surface of the Floridan aquifer in the Northwest Florida Water Management District, May 1976  

USGS Publications Warehouse

This map shows the potentiometric surface of the Floridan aquifer in the Florida Panhandle. Contour intervals of 10 feet show altitude at which water level would have stood in tightly cased wells. Datum is mean sea level. Locations of observation wells also are shown. (Woodard-USGS)

Rosenau, J. C.; Meadows, P. E.

1976-01-01

304

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

305

Polypyrrole based amperometric and potentiometric phosphate biosensors: a comparative study B.  

PubMed

The preparation of two electrochemical (potentiometric and amperometric) phosphate biosensors is described and compared. Purine nucleoside phosphorylase (PNP) and xanthine oxidase (XOD) were co-immobilized via entrapment into polypyrrole (PPy) films by galvanostatic polymerization. Polypyrrole entrapment was achieved with 0.5M pyrrole by using a polymerization time of 200 s and a mole ratio of 1:8 (6.2U/mL XOD: 49.6 U/mL PNP) in amperometric phosphate biosensor. Potentiometric bi-layer biosensor PPy-NO(3)/BSA-GLA-PNP-XOD is made of an inner electropolymerized PPy-NO(3) layer and an outer layer of PNP and XOD cross-linked with a mixture of bovine serum albumen (BSA) and gultaraldehyde (GLA).The optimum conditions for potentiometric bi-layer biosensor include a polymerization time of 300 s for the inner layer at an applied current density of 0.25 mA cm(-2), a drying time of 30 min for the outer layer, pH 7, and 0.025MTris-HCl. Sensitive amperometric measurements obtained from PPy-PNP-XOD-Fe(CN)(6)(4-) biosensors were compared with those of potentiometric measurements obtained from PPy-NO(3)/BSA/GLA-PNP-XOD bi-layer biosensor. A minimum detectable concentration of 20.0 ?M phosphates and a linear concentration range of 20-200 ?M were achieved with potentiometric PPy-NO(3)/BSA/GLA-PNP-XOD biosensor. In comparison, a minimum detectable concentration of 10 ?M and a linear concentration range of 0.1-1 mM were achieved with amperometric biosensor. The presence of uric and ascorbic acids had the least effect on the performance of the PPy-PNP-XOD-Fe(CN)(6)(4-) amperometric and PPy-NO(3)/BSA/GLA-PNP-XOD potentiometric bi-biosensors, therefore, they will not have any effect on phosphate measurement in both biosensors at levels normally present in water. PPy-NO(3)/BSA-GLA-PNP-XOD potentiometric biosensor was used to analyse phosphate in real samples. PMID:23021852

Lawal, Abdulazeez T; Adeloju, Samuel B

2012-08-25

306

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

307

Acid–base equilibria in systems involving substituted pyridines in polar aprotic protophobic media and in the amphiprotic methanol  

Microsoft Academic Search

Acid dissociation, as well as cationic homo- and heteroconjugation constants have been determined by potentiometric titration in systems involving substituted pyridines and conjugate cationic acids in the polar protophobic aprotic solvent acetone and in polar amphiprotic methanol. The values of the constant were compared with those previously determined in other polar protophobic aprotic solvents, acetonitrile, nitromethane and propylene carbonate. The

D Augustin-Nowacka; M Makowski; L Chmurzynski

2000-01-01

308

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

309

Polyoxometalates on cationic silica  

Microsoft Academic Search

Binary cupric nitrate and triflate systems catalyze the homogeneous air oxidation of the mustard (HD) simulant 2-chloroethyl ethyl sulfide (CEES) to the corresponding desired sulfoxide (CEESO) with effectively quantitative selectivity in acetonitrile under ambient conditions. This activity is enhanced when cationic silica nanoparticles coated with the anionic multi-iron polyoxometalates (POMs) are also present. The POM-coated nanoparticles are prepared by treatment

Nelya M. Okun; Travis M. Anderson; Craig L. Hill

2003-01-01

310

Common standards of basal insulin titration in type 2 diabetes.  

PubMed

Type 2 diabetes mellitus has become a worldwide major health problem, and the number of people affected is steadily increasing. Thus, not all patients suffering from the disease can be treated by specialized diabetes centers or outpatient clinics, but by primary care physicians. The latter, however, might have time constraints and have to deal with many kinds of diseases or with multimorbid patients, so their focus is not so much on lowering high blood glucose values. Thus, the physicians, as well as the patients themselves, are often reluctant to initiate and adjust insulin therapy, although basal insulin therapy is considered the appropriate strategy after oral antidiabetic drug failure, according to the latest international guidelines. A substantial number of clinical studies have shown that insulin initiation and optimization can be managed successfully by using titration algorithms-even in cases where patients themselves are the drivers of insulin titration. Nevertheless, tools and strategies are needed to facilitate this process in the daily life of both primary health care professionals and patients with diabetes. PMID:23759411

Arnolds, Sabine; Heise, Tim; Flacke, Frank; Sieber, Jochen

2013-05-01

311

Theoretical curves in indicator photometric titration of monodentate polyatomic ligands by metal ions  

SciTech Connect

On the basis of the law of mass action and material balance conditions, theoretical equations have been derived for the curves obtained in indicator photometric titration of anionic ligands by metal ions for the cases of formation of complexes ML, M/sub 2/L, and ML/sub 2/. Correspondence between theoretical and experimental titration curves has been demonstrated, thus making it possible to explain the factual material and to use reactions of low-stability complex formation in photometric titrations.

Kuznetsov, V.V.; Shamanskii, V.A.

1986-03-20

312

Sodium Determination Using Ion Selective Electrodes, Mohr Titration, and Test Strips  

NASA Astrophysics Data System (ADS)

Sodium content of foods can be determined by various methods, including an ion selective electrode (ISE), the Mohr or Volhard titration procedure, or indicator test strips. These methods are official methods of analysis for numerous specific products. All these methods are faster and less expensive procedures than analysis by atomic absorption spectroscopy or inductively coupled plasma-atomic emission spectroscopy. This experiment allows one to compare sodium analysis of several food products by ISE, Mohr titration, and Quantab® chloride titrators.

Nielsen, S. Suzanne

313

Efficacy of daytime continuous positive airway pressure titration in severe obstructive sleep apnoea  

Microsoft Academic Search

Efficacy of daytime continuous positive airway pressure titration in severe obstructive sleep apnoea. J.C. Rudkowski, P. Verschelden, R.J. Kimoff. #ERS Journals Ltd 2001. ABSTRACT: The aim of this study was to evaluate manual nasal continuous positive airway pressure (nCPAP) titration during daytime polysomnography compared with conventional overnight titration for patients with severe obstructive sleep apnoea. Thirty-two patients who underwent daytime

J. C. Rudkowski; P. Verschelden; R. J. Kimoff

2001-01-01

314

Formation and calcination temperature-dependent sintering activity of YAG precursor synthesized via reverse titration method  

Microsoft Academic Search

The composition homogeneity of YAG precursors synthesized via both normal and reverse titration co-precipitation methods is discussed. It was demonstrated that that the reverse titration process possesses better co-precipitation characteristics than the normal titration process, based on a real-time monitoring of the reaction pH and measurement of the Y\\/Al ratio in the precipitate. The formation process of the precipitate obtained

Yuanhua Sang; Hong Liu; Xudong Sun; Xiaolin Zhang; Haiming Qin; Yaohui Lv; Di Huo; Duo Liu; Jiyang Wang; Robert I. Boughton

2011-01-01

315

Isothermal Titration Calorimetry for Measuring Macromolecule-Ligand Affinity  

PubMed Central

Isothermal titration calorimetry (ITC) is a useful tool for understanding the complete thermodynamic picture of a binding reaction. In biological sciences, macromolecular interactions are essential in understanding the machinery of the cell. Experimental conditions, such as buffer and temperature, can be tailored to the particular binding system being studied. However, careful planning is needed since certain ligand and macromolecule concentration ranges are necessary to obtain useful data. Concentrations of the macromolecule and ligand need to be accurately determined for reliable results. Care also needs to be taken when preparing the samples as impurities can significantly affect the experiment. When ITC experiments, along with controls, are performed properly, useful binding information, such as the stoichiometry, affinity and enthalpy, are obtained. By running additional experiments under different buffer or temperature conditions, more detailed information can be obtained about the system. A protocol for the basic setup of an ITC experiment is given.

Duff, Jr., Michael R.; Grubbs, Jordan; Howell, Elizabeth E.

2011-01-01

316

SSB binding to ssDNA using isothermal titration calorimetry.  

PubMed

Isothermal titration calorimetry (ITC) is a powerful method for studying protein-DNA interactions in solution. As long as binding is accompanied by an appreciable enthalpy change, ITC studies can yield quantitative information on stoichiometries, binding energetics (affinity, binding enthalpy and entropy) and potential site-site interactions (cooperativity). This can provide a full thermodynamic description of an interacting system which is necessary to understand the stability and specificity of protein-DNA interactions and to correlate the activities or functions of different species. Here we describe procedures to perform and analyze ITC studies using as examples, the E. coli SSB (homotetramer with 4 OB-folds) and D. radiodurans SSB (homodimer with 4 OB-folds). For oligomeric protein systems such as these, we emphasize the need to be aware of the likelihood that solution conditions will influence not only the affinity and enthalpy of binding but also the mode by which the SSB oligomer binds ssDNA. PMID:22976176

Kozlov, Alexander G; Lohman, Timothy M

2012-01-01

317

Revisiting the optimal c value for isothermal titration calorimetry.  

PubMed

The precision with which the dissociation constant, K(D), can be obtained from isothermal titration calorimetry depends on, among other factors, the concentrations of the interacting species. The so-called c value-the ratio of analyte concentration to K(D)-should fall in the range of 1 to 1000 for reliable K(D) determination. On the basis of simulated, noise-free data, Biswas and Tsodikov [5] recently suggested an optimal c value of 5 to 20. By contrast, we find an optimum at c > 40 on determining the K(D) confidence intervals through simulations containing noise levels typical of state-of-the-art microcalorimeters. PMID:21854755

Broecker, Jana; Vargas, Carolyn; Keller, Sandro

2011-07-30

318

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

2013-09-17

319

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?

2007-04-08

320

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

321

Potentiometric sensor for determination of neutral bisphenol A using a molecularly imprinted polymer as a receptor.  

PubMed

The aim of this paper is to develop a potentiometric sensing methodology for sensitive and selective determination of neutral phenols by using a molecularly imprinted polymer as a receptor. Bisphenol A (BPA), a significant environmental contaminant, is employed as the model target. The BPA-imprinted polymer is synthesized by the semi-covalent technique and incorporated into a plasticized poly(vinyl chloride) membrane doped with the tridodecylmethylammonium salt. The present electrode shows a linear anionic potential response over the concentration range from 0.1 to 1 ?M with a detection limit of 0.02 ?M, and exhibits an excellent selectivity over other phenols. The proposed approach has been successfully applied to the determination of BPA released from real plastic samples. It offers promising potential in development of potentiometric sensors for measuring neutral phenols at trace levels. PMID:23512188

Kou, Li-Juan; Liang, Rong-Ning; Wang, Xue-Wei; Chen, Yan; Qin, Wei

2013-03-20

322

Potentiometric sensing of chemical warfare agents: surface imprinted polymer integrated with an indium tin oxide electrode.  

PubMed

Rapid and specific recognition of methylphosphonic acid (MPA), the degradation product of nerve agents sarin, soman, VX, etc., was achieved with potentiometric measurements using a chemical sensor fabricated by a surface imprinting technique coupled with a nanoscale transducer, indium tin oxide (ITO). An octadecylsiloxane thin layer was covalently bound to the ITO-coated glass surface in the presence of MPA. After extraction of MPA, potentiometric measurements showed selective detection of MPA. The selectivity of the sensor has been tested on other alkylphosphonic acids, such as ethylphosphonic acid and propylphosphonic acid, as well as tert-butylphosphonic acid. The viability of the sensor in the presence of other chemical analogues, such as organophosphorus pesticides and herbicides, was investigated. PMID:15144176

Zhou, Yanxiu; Yu, Bin; Shiu, Eric; Levon, Kalle

2004-05-15

323

Potentiometric determination of tolterodine in batch and flow injection conditions.  

PubMed

Two new ion-selective electrodes of the plastic membrane type for the determination of Tolterodine (Tol) were prepared. These electrodes depend on the incorporation of the ion-exchangers of the above mentioned drug with phosphotungestic acid (PTA) or Silicotungestic acid (STA) in a PVC matrix. A comparative study is made between the performance characteristics of electrodes containing ion-exchanger in batch and FIA conditions. The usable concentration range of the electrodes was found to be (1.0×10(-5)-1.0×10(-2) and 5.0×10(-5)-1.0×10(-2)M) in batch and FIA conditions, respectively. The electrodes have nearly the same usable concentration, pH range and exhibited high selectivity toward Tol in the presence of many inorganic cations and can be used in biological fluids such as urine and plasma. The dissolution profile of the investigated drug as well as its assay in pure and pharmaceutical preparations was performed, and the results were relatively accurate and precise as indicated by the recovery values and coefficients of variation. PMID:22817943

Sakr, Marwa M; El Nashar, Rasha M

2012-02-28

324

A micro-potentiometric hemoglobin immunosensor based on electropolymerized polypyrrole–gold nanoparticles composite  

Microsoft Academic Search

We report a novel micro-potentiometric hemoglobin (Hb) immunosensor based on electrochemically synthesized polypyrrole (PPy)–gold nanoparticles (AuNPs) composite. PPy–AuNPs film with AuNPs uniformly distributed in it was deposited on gold electrode surface by a simple and direct procedure, without the addition of any nanoparticles or reducing agent. And this generic method makes it possible to deposite different polymers on miniaturized electrodes.

Lan Qu; Shanhong Xia; Chao Bian; Jizhou Sun; Jinghong Han

2009-01-01

325

Flow injection potentiometric determination of total antioxidant activity of plant extracts  

Microsoft Academic Search

A new flow injection potentiometric (FIP) method, rapid, reproducible and simple to apply, has been developed for the in vitro evaluation of antioxidative capacity of aqueous plant extracts. This method is based on the transient negative signal measurements with a flow-type platinum electrode detector due to the composition change of a [Fe(CN)6]3?\\/[Fe(CN)6]4? redox-reagent solution. The variables affecting the signal height

Liliya K. Shpigun; Marina A. Arharova; Khena Z. Brainina; Alla V. Ivanova

2006-01-01

326

Simultaneous potentiometric and fluorimetric determination of diclofenac in a sequential injection analysis system  

Microsoft Academic Search

Two independent methods for the determination of diclofenac were simultaneously implemented in an automated analytical system, based on the concept of sequential injection analysis, providing real-time assessment of results quality. The potentiometric detection was carried out with an ion-selective electrode based on a cyclodextrin while for the fluorimetric determination the sample was previously subject to in-line irradiation with UV light.

A. M Pimenta; A. N Araújo; M. C. B. S. M Montenegro

2002-01-01

327

Neurochip based on light-addressable potentiometric sensor with wavelet transform de-noising  

Microsoft Academic Search

Neurochip based on light-addressable potentiometric sensor (LAPS), whose sensing elements are excitable cells, can monitor\\u000a electrophysiological properties of cultured neuron networks with cellular signals well analyzed. Here we report a kind of\\u000a neurochip with rat pheochromocytoma (PC12) cells hybrid with LAPS and a method of de-noising signals based on wavelet transform.\\u000a Cells were cultured on LAPS for several days to

Qing-jun Liu; Wei-wei Ye; Hui Yu; Ning Hu; Li-ping Du; Ping Wang

2010-01-01

328

Investigation on light-addressable potentiometric sensor as a possible cell–semiconductor hybrid  

Microsoft Academic Search

This article reports an investigation on light-addressable potentiometric sensor (LAPS) to be used as a possible biological cell–semiconductor hybrid that will enable us to make an interface between the physical and biological system. To increase the surface potential sensitivity, we used a LAPS structure with single insulator (SiO2) coated with poly-l-ornithine and laminin (PLOL) on Si. Efficient culturing of PC-12

Tatsuo Yoshinobu; Hiroshi Iwasaki; Hirokazu Sugihara; Tetsuo Yukimasa; Isao Hirata; Hiroo Iwata

2003-01-01

329

Cell-based biosensors based on light-addressable potentiometric sensors for single cell monitoring  

Microsoft Academic Search

Cell-based biosensors incorporate cells as sensing elements that convert changes in immediate environment to signals for processing. This paper reports an investigation on light-addressable potentiometric sensor (LAPS) to be used as a possible cell-base biosensor that will enable us to monitor extracellular action potential of single living cell under stimulant. In order to modify chip surface and immobilize cells, we

Gaixia Xu; Xuesong Ye; Lifeng Qin; Ying Xu; Yan Li; Rong Li; Ping Wang

2005-01-01

330

Detection of plasmids using DNA and RNA probes and the light-addressable potentiometric sensor  

Microsoft Academic Search

Intact plasmids, plasmid fragments, and cDNA were detected using two DNA or RNA probes of varying lengths, each containing only biotin or fluorescein molecules. The probes were hybridized with the target plasmid\\/cDNA, bound with streptavidin, captured on nitrocellulose membranes, and detected using the urease-conjugate of an anti-fluorescein antibody via the light-addressable potentiometric sensor. The output of the silicon-chip sensor is

Kilian Dill; Samuel D. H Chan; Thomas W Gibbs

1997-01-01

331

Extracellular measurements of averaged ionic currents with the light-addressable potentiometric sensor (LAPS)  

Microsoft Academic Search

The light-addressable potentiometric sensor (LAPS) is a silicon-based detector which allows for measuring the electric potential distribution along its surface. The point of measurement is determined by illumination with a pulsed light source, and therefore the surface potential distribution can be measured spatially resolved by raster scanning a light-pointer along the surface. In this study electrically excitable neuronal cells (N1-E115

B. Stein; M. George; H. E. Gaub; W. J. Parak

2004-01-01

332

Constant-phase-mode operation of the light-addressable potentiometric sensor  

Microsoft Academic Search

The constant-phase-mode operation of the light-addressable potentiometric sensor (LAPS) is proposed and demonstrated. In this new operation mode, the temporal change and the spatial distribution of the analyte concentration are recorded in the form of the bias voltage applied to the LAPS sensor plate, which is servo-controlled to maintain the phase of the photocurrent at a constant value with respect

Ko-ichiro Miyamoto; Torsten Wagner; Shuhei Mimura; Shin’ichiro Kanoh; Tatsuo Yoshinobu; Michael J. Schöning

2011-01-01

333

Light-addressable potentiometric penicillin image sensor using the self-assembled monolayer immobilizing method  

Microsoft Academic Search

In this study, the LAPSs (light addressable potentiometric sensors) which have devices of Si3N4\\/SiO2\\/Si, Ta2O5\\/SiO2\\/Si structure were fabricated. Also, it was investigated the response characteristics to penicillin concentration and detected the 2D images of 128 × 128 pixels. The penicillinase was immobilized on the devices to hydrolyze the penicillin using self-assembled monolayer (SAM) method. The measuring system was simplified by

Su-Won Jang; Sun-Young Lee; Kwang-Man Lee; Dae-Hyuk Kwon; Shin-Won Kang

2005-01-01

334

Constant-phase-mode operation of the light-addressable potentiometric sensor  

Microsoft Academic Search

We herein propose and demonstrate the constant-phase-mode operation of the light-addressable potentiometric sensor (LAPS). The bias voltage applied to the LAPS sensor plate is servo-controlled to maintain the phase of the photocurrent with respect to the light modulation at a constant value. In this new operation mode, the temporal change and the spatial distribution of the potential at the sensing

Ko-ichiro Miyamoto; Torsten Wagner; Shuhei Mimura; Shin'ichiro Kanoh; Tatsuo Yoshinobu; Michael J. Schöning

2009-01-01

335

The light-addressable potentiometric sensor for multi-ion sensing and imaging  

Microsoft Academic Search

The light-addressable potentiometric sensor (LAPS) is a semiconductor-based chemical sensor with an electrolyte–insulator–semiconductor structure. The LAPS can have many measuring points integrated on the sensing surface, which are individually accessed by a light beam. By modifying the measuring points with different materials, a single sensor plate can be used as a multi-analyte sensor. In this paper, instrumentation and application of

T. Yoshinobu; H. Iwasaki; Y. Ui; K. Furuichi; Yu. Ermolenko; Yu. Mourzina; T. Wagner; N. Näther; M. J. Schöning

2005-01-01

336

Photocurable membranes for ion-selective light-addressable potentiometric sensor  

Microsoft Academic Search

A new type of light-addressable potentiometric sensor (LAPS) has been developed by elaboration of photocurable ion-sensitive membranes based on matrices of mono- and diacrylates in combination with a silicon-based electrochemical transducer for the purposes of chemical and biochemical analyses. The characteristics of the elaborated K-, Li-, Cs-, Ca- and Mg-LAPS are presented to indicate the potential of the technology developed.

Yu. Ermolenko; T. Yoshinobu; Yu. Mourzina; S. Levichev; K. Furuichi; Yu. Vlasov; M. J. Schöning; H. Iwasaki

2002-01-01

337

Picogram detection levels of asialofetuin via the carbohydrate moieties using the light addressable potentiometric sensor  

Microsoft Academic Search

Fetal calf serum asialofetuin was assayed in the sandwich format using biotinylated and fluoresceinated ricin toxin (B-RCA and F-RCA). The sandwiched species was captured on a biotin-BSA coated nitrocellulose membrane with streptavidin. Anti-fluorescein antibody-urease conjugate was bound to the complex, and detected and quantitated under microvolume conditions using the light addressable potentiometric sensor. As little as 250 pg of asialofetuin

Kilian Dill; John D. Olson

1995-01-01

338

Light Addressable Potentiometric Sensor with Fluorine-Terminated Hafnium Oxide Layer for Sodium Detection  

Microsoft Academic Search

In this study, post-CF4 plasma surface treatment of light addressable potentiometric sensor (LAPS) with a HfO2-sensing membrane was carried out. pH sensitivity decreased but pNa sensitivity increased with fluorine incorporation. The highest pNa sensitivity was 31.8 mV\\/pNa, which was optimized with 3 min post CF4 plasma treatment. The results showed a high possibility for sensing sodium ions using an inorganic-sensing

Cheng-En Lue; Chao-Sung Lai; Hsin-Yu Chen; Chia-Ming Yang

2010-01-01

339

Rigorous Potentiometric Determination of Metal Complexes Stability Constants: An Undergraduate Laboratory Practice  

NASA Astrophysics Data System (ADS)

In the present work an undergraduate laboratory practice is described corresponding to both experimental and computational methods used in potentiometric equilibrium constants determinations. As an example of these determinations the system formed by Cu(II) and D-galacturonic acid was selected. Both the deprotonation constant for the ligand and the equilibrium constants for the metal chelates were determined by using the program BEST.

Escandar, Graciela M.; Federico Sala, Luis

1997-11-01

340

Novel naphthylstyryl-pyridinium potentiometric dyes offer advantages for neural network analysis  

Microsoft Academic Search

The submucous plexus of the guinea pig intestine is a quasi-two-dimensional mammalian neural network that is particularly amenable to study using multiple site optical recording of transmembrane voltage (MSORTV) [Biol. Bull. 183 (1992) 344; J. Neurosci. 19 (1999) 3073]. For several years the potentiometric dye of choice for monitoring the electrical activity of its individual neurons has been di-8-ANEPPS [Neuron

A. L. Obaid; L. M. Loew; J. P. Wuskell; B. M. Salzberg

2004-01-01

341

Potentiometric cholesterol biosensor based on ZnO nanorods chemically grown on Ag wire  

Microsoft Academic Search

An electrochemical biosensor based on ZnO nanorods for potentiometric cholesterol determination is proposed. Hexagon-shaped ZnO nanorods were directly grown on a silver wire having a diameter of 250?m using low temperature aqueous chemical approach that produced ZnO nanorods with a diameter of 125–250nm and a length of ~1?m. Cholesterol oxidase (ChOx) was immobilized by a physical adsorption method onto ZnO

M. Q. Israr; J. R. Sadaf; M. H. Asif; O. Nur; M. Willander; B. Danielsson

2010-01-01

342

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

343

Potentiometric pH sensor based on an oil paste containing quinhydrone  

Microsoft Academic Search

An all-solid-state potentiometric pH sensor based on the dispersion of quinhydrone in carbon paste was developed. Quinhydrone was incorporated in a soft membrane that was in contact with a conducting wire via a conducting paste. This configuration overcomes the problem of fragility that is encountered in the glass electrode. This membrane is robust, reusable and renewable. The sensing membrane was

Joyce Tan; M. Lacson

2005-01-01

344

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

345

Screen-printed sensor for batch and flow injection potentiometric chromium(VI) monitoring.  

PubMed

A disposable screen-printed electrode was designed and evaluated for direct detection of chromium(VI) in batch and flow analysis. The carbon screen-printed electrode was modified with a graphite-epoxy composite. The optimal graphite-epoxy matrix contains 37.5% graphite powder, 12.5% diphenylcarbohydrazide, a selective compound for chromium(VI), and 50% epoxy resin. The principal analytical parameters of the potentiometric response in batch and flow analysis were optimized and calculated. The screen-printed sensor exhibits a response time of 20 +/- 1 s. In flow analysis, the analytical frequency of sampling is 70 injections per hour using 0.1 M NaNO(3) solution at pH 3 as the carrier, a flow rate of 2.5 mL.min(-1), and an injection sample volume of 0.50 mL. The sensor shows potentiometric responses that are very selective for chromium(VI) ions and optimal detection limits in both static mode (2.1 x 10(-7) M) and online analysis (9.4 x 10(-7) M). The disposable potentiometric sensor was employed to determine toxicity levels of chromium(VI) in mineral, tap, and river waters by flow-injection potentiometry and batch potentiometry. Chromium(VI) determination was also carried out with successful results in leachates from municipal solid waste landfills. PMID:20107772

Sánchez-Moreno, Raúl A; Gismera, M Jesús; Sevilla, M Teresa; Procopio, Jesús R

2010-01-27

346

Propofol Alone Titrated to Deep Sedation Versus Propofol in Combination with Opioids and\\/or Benzodiazepines and Titrated to Moderate Sedation for Colonoscopy  

Microsoft Academic Search

BACKGROUND:Propofol by nonanesthesiologists is controversial because the drug is commonly used to produce deep sedation or general anesthesia. Propofol in combination with opioids and\\/or benzodiazepines can be titrated to moderate sedation, which might be safer.AIM:To compare recovery time, patient satisfaction, and other end points with propofol alone titrated to deep sedation versus propofol combination therapy with opioids and\\/or benzodiazepines.METHOD:A randomized

Megan E. VanNatta; Douglas K. Rex

2006-01-01

347

Macromolecular competition titration method accessing thermodynamics of the unmodified macromolecule-ligand interactions through spectroscopic titrations of fluorescent analogs.  

PubMed

Analysis of thermodynamically rigorous binding isotherms provides fundamental information about the energetics of the ligand-macromolecule interactions and often an invaluable insight about the structure of the formed complexes. The Macromolecular Competition Titration (MCT) method enables one to quantitatively obtain interaction parameters of protein-nucleic acid interactions, which may not be available by other methods, particularly for the unmodified long polymer lattices and specific nucleic acid substrates, if the binding is not accompanied by adequate spectroscopic signal changes. The method can be applied using different fluorescent nucleic acids or fluorophores, although the etheno-derivatives of nucleic acid are especially suitable as they are relatively easy to prepare, have significant blue fluorescence, their excitation band lies far from the protein absorption spectrum, and the modification eliminates the possibility of base pairing with other nucleic acids. The MCT method is not limited to the specific size of the reference nucleic acid. Particularly, a simple analysis of the competition titration experiments is described in which the fluorescent, short fragment of nucleic acid, spanning the exact site-size of the protein-nucleic acid complex, and binding with only a 1:1 stoichiometry to the protein, is used as a reference macromolecule. Although the MCT method is predominantly discussed as applied to studying protein-nucleic acid interactions, it can generally be applied to any ligand-macromolecule system by monitoring the association reaction using the spectroscopic signal originating from the reference macromolecule in the presence of the competing macromolecule, whose interaction parameters with the ligand are to be determined. PMID:21195223

Bujalowski, Wlodzimierz; Jezewska, Maria J

2011-01-01

348

Evidence for Antiferromagnetic Order in Bi 2Sr 2CuO 6Phase with Stoichiometric Cation Composition  

Microsoft Academic Search

We have succeeded in synthesizing the insulating phase of Bi2Sr2CuO6+?(Bi2201) with the stoichiometric cation composition by use of a heat treatment technique in an evacuated tube with titanium powders. The excess oxygen content?and the average valence of Bi were determined electrochemically by the coulometric titration method. The value of?in the insulating phase was found to be 0.02. The hole concentrationhwas

Masaki Kato; Kazuyoshi Yoshimura; Koji Kosuge

1997-01-01

349

The adsorption of cationic and amphoteric copolymers on glass surfaces: zeta potential measurements, adsorption isotherm determination, and FT Raman characterization.  

PubMed

The adsorption of cationic and amphoteric copolymers onto controlled pore glass (CPG) powders has been studied by measurement of the powder particle zeta (zeta) potential, by determination of the adsorption isotherm, and by FT Raman measurements of the polymer-coated powder. The cationic polymers consisted chiefly of homopolymers of dimethyldiallylammonium chloride (DMDAAC) or copolymers of DMDAAC and acrylamide. The amphoteric polymers studied included copolymers of DMDAAC and acrylic acid. The comonomer ratio was varied to explore the dependence of cationic charge density on the extent and effect of adsorption. Both types of polymers adsorb onto the anionic glass surface via an ion-exchange mechanism. Consequently, a correspondingly higher mass of a low-charge-density copolymer adsorbs than of a cationic homopolymer. The presence of the anionic portion in the amphoteric polymers does not significantly alter this picture. The zeta potential, however, reflects the overall nature of the polymer. Cationic polymers effectively neutralize the glass surface, while amphoteric polymers leave the zeta potential net negative. Adsorption isotherms, determined via the depletion technique using colloidal titration, were used to "calibrate" a FT Raman method. The latter was used to determined the amount of adsorbed polymer under solution conditions in which colloidal titration could not be performed. PMID:12909030

Tartakovsky, Alla; Drutis, Dane M; Carnali, Joseph O

2003-07-15

350

Attacking Class Certifi cation Motions  

Microsoft Academic Search

Two recent post-Tobacco II Court of Appeal cases suggest that such reliance cannot necessarily be presumed. Two Court of Appeal panels in Southern California affi rmed trial court orders denying class certifi cation, drawing a distinction between the standing requirements and the other requirements for class certifi cation. The Court of Appeal for the 2nd Appellate District issued a decision

Charles T. Munger; Gerald L. Salzman; David Houston

2009-01-01

351

Molecular modelling of cation–? interactions  

Microsoft Academic Search

Cation–? interactions have long been considered a challenge for molecular modelling and a shortcoming of most of the commonly used biomolecular force fields. In this article, we provide an overview of current research on molecular modelling of cation–? interactions, with an emphasis on applications to proteins and on our recent polarisable models based on the classical Drude oscillator. We describe

Guillaume Lamoureux; Esam A. Orabi

2012-01-01

352

ZP3-dependent activation of sperm cation channels regulates acrosomal secretion during mammalian fertilization  

PubMed Central

The sperm acrosome reaction is a Ca(2+)-dependent secretory event required for fertilization. Adhesion to the egg's zona pellucida promotes Ca2+ influx through voltage-sensitive channels, thereby initiating secretion. We used potentiometric fluorescent probes to determine the role of sperm membrane potential in regulating Ca2+ entry. ZP3, the glycoprotein agonist of the zona pellucida, depolarizes sperm membranes by activating a pertussis toxin-insensitive mechanism with the characteristics of a poorly selective cation channel. ZP3 also activates a pertussis toxin-sensitive pathway that produces a transient rise in internal pH. The concerted effects of depolarization and alkalinization open voltage-sensitive Ca2+ channels. These observations suggest that mammalian sperm utilize membrane potential-dependent signal transduction mechanisms and that a depolarization pathway is an upstream transducing element coupling adhesion to secretion during fertilization.

1996-01-01

353

The Determination of the Points of Zero Charge of Fine Mineral Particles by a Titration Technique.  

National Technical Information Service (NTIS)

The Bureau of Mines has developed a simple titration technique for determining the points of zero charge (PZC) on minerals. The technique consists of titrating a mineral slurry with the potassium salt of polyvinyl sulfuric acid (PVSK) in the presence of a...

D. A. Stanley P. M. Brown B. J. Scheiner

1982-01-01

354

Membrane Surface-Charge Titration Probed by Gramicidin A Channel Conductance  

Microsoft Academic Search

We manipulate lipid bilayer surface charge and gauge its influence on gramicidin A channel conductance by two strategies: titration of the lipid charge through bulk solution pH and dilution of a charged lipid by neutral. Using diphytanoyl phosphatidylserine (PS) bilayers with CsCl aqueous solutions, we show that the effects of lipid charge titration on channel conductance are masked 1) by

Tatiana K. Rostovtseva; Vicente M. Aguilella; Igor Vodyanoy; Sergey M. Bezrukov; V. Adrian Parsegian

1998-01-01

355

Sertraline treatment of obsessive-compulsive disorder: efficacy and tolerability of a rapid titration regimen  

Microsoft Academic Search

The objective of this study was to compare in a single blind manner, over a period of 12 weeks, the efficacy and tolerability of two different titration regimens of sertraline in the treatment of OCD: 150 mg\\/day reached at day five from the beginning of therapy (rapid titration regimen) versus 150 mg\\/day reached at day 15 from the beginning (slow

Filippo Bogetto; Umberto Albert; Giuseppe Maina

2002-01-01

356

Equivalency testing of procedures for measuring free available chlorine: amperometric titration, DPD, and FACTS  

Microsoft Academic Search

The results of 192 analyses for free available chlorine were obtained from each of 16 participating laboratories. These data were statistically analyzed to determine whether the DPD, FACTS, and amperometric titration methods were equivalent. This analysis indicated that FACTS is equivalent to both DPD and amperometric titration.

William J. Cooper; Paul H. Gibbs; Edward M. Ott; Perin Patel

1983-01-01

357

SIMPLE FLOW INJECTION TITRATION METHOD BASED ON VARIATION OF THE SAMPLE VOLUME  

Microsoft Academic Search

A simple single-line flow injection system incorporating the fully rotary valve (FRV) has been developed for titration purposes. The FRV enables to inject the titrand solution to the titrant stream in four different volumes producing a set of four adequate analytical signals. Due to this fact the titration procedure can be performed with the use of only two standard solutions

Pawe? Ko?cielniak; Joanna Kozak

2002-01-01

358

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

359

Role of different nocturnal monitorings in the evaluation of CPAP titration by autoCPAP devices.  

PubMed

The aim of the study was to assess how the analysis of different signals recorded during application of automatic continuous positive airway pressure (autoCPAP) devices improves the evaluation of pressure titration in patients with obstructive sleep apnea syndrome (OSAS) naive to treatment. Seventy-two patients underwent nocturnal polysomnography during autoCPAP (Autoset T, ResMed, Sydney, Australia) application. Progressively more complex combinations of signals were analysed in consecutive steps. According to the analysis of oxyhemoglobin saturation (SaO(2)) alone, a fixed CPAP level suitable for treatment could not be identified in 3 subjects. When analysis of posture was added, titration was considered unsatisfactory in 1 more subject, due to a short time spent supine. Further, addition of flow and respiratory movements led to consider titration unsatisfactory in 1 more subject. Analysis of all polysomnographic signals demonstrated a not fully reliable titration in 9 subjects: 1 with short sleep duration, 2 without REM sleep, 4 with a short sleep time spent supine, and 3 subjects (already identified by SaO(2)) with insufficient correction of respiratory disorders even when a relatively high CPAP was administered. Mask leaks did not hamper titration. CPAP titration by automatic devices alone results in imperfect titration in >10% subjects naive to ventilatory treatment. Only polysomnographic recording ensures titration reliability in all patients. Further research is needed to identify simple and economic methods to reliably start the CPAP treatment. PMID:15733507

Marrone, Oreste; Insalaco, Giuseppe; Salvaggio, Adriana; Bonsignore, Giovanni

2005-03-01

360

Efficacy of daytime continuous positive airway pressure titration in severe obstructive sleep apnoea.  

PubMed

The aim of this study was to evaluate manual nasal continuous positive airway pressure (nCPAP) titration during daytime polysomnography compared with conventional overnight titration for patients with severe obstructive sleep apnoea. Thirty-two patients who underwent daytime titration were retrospectively matched (for age, sex, body mass index and apnoea/hypopnoea index (AHI)) to a group titrated overnight during the same period. Successful titration was defined as the identification of the nCPAP level (effective nCPAP (Peff)) required to eliminate respiratory events during all sleep stages. After 3 months of therapy on nCPAP at Peff, nCPAP utilization history was obtained and a group of patients underwent a repeat polysomnogram (PSG) and completed a follow-up Epworth Sleepiness Scale (ESS) score. Initial titration was successful in 91% of daytime patients and 91% of overnight patients. The success of daytime titration was not related to diagnostic AHI or ESS score. Subjective nCPAP utilization was statistically similar in both groups. On the follow-up PSG, there were no significant differences between daytime (n=11) and overnight (n=11) patients in measures of sleep quality or respiratory disturbance. Both groups demonstrated similar and significant improvements in ESS score. These findings suggest that the effective nasal continuous positive airway pressure can be accurately established during daytime titration in a substantial proportion of severe, symptomatic obstructive sleep apnoea patients. PMID:11589352

Rudkowski, J C; Verschelden, P; Kimoff, R J

2001-09-01

361

Potentiometric Surface of the Upper Floridan Aquifer, West-Central Florida, September 2007  

USGS Publications Warehouse

The Floridan aquifer system consists of the Upper and Lower Floridan aquifers separated by the middle confining unit. The middle confining unit and the Lower Floridan aquifer in west-central Florida generally contain highly mineralized water. The water-bearing units containing fresh water are herein referred to as the Upper Floridan aquifer. The Upper Floridan aquifer is the principal source of water in the Southwest Florida Water Management District and is used for major public supply, domestic use, irrigation, and brackish water desalination in coastal communities (Southwest Florida Water Management District, 2000). This map report shows the potentiometric surface of the Upper Floridan aquifer measured in September 2007. The potentiometric surface is an imaginary surface connecting points of equal altitude to which water will rise in tightly-cased wells that tap a confined aquifer system (Lohman, 1979). This map represents water-level conditions near the end of the wet season, when ground-water levels usually are at an annual high and withdrawals for agricultural use typically are low. The cumulative average rainfall of 39.50 inches for west-central Florida (from October 2006 through September 2007) was 13.42 inches below the historical cumulative average of 52.92 inches (Southwest Florida Water Management District, 2007). Historical cumulative averages are calculated from regional rainfall summary reports (1915 to most recent complete calendar year) and are updated monthly by the Southwest Florida Water Management District. This report, prepared by the U.S. Geological Survey in cooperation with the Southwest Florida Water Management District, is part of a semi-annual series of Upper Floridan aquifer potentiometric-surface map reports for west-central Florida. Potentiometric-surface maps have been prepared for January 1964, May 1969, May 1971, May 1973, May 1974, and for each May and September since 1975. Water-level data are collected in May and September each year to show the approximate annual low and high water-level conditions, respectively. Most of the water-level data for this map were collected by the U.S. Geological Survey during the period September 17-21, 2007. Supplemental water-level data were collected by other agencies and companies. A corresponding potentiometric-surface map was prepared for areas east and north of the Southwest Florida Water Management District boundary by the U.S. Geological Survey office in Orlando, Florida (Kinnaman and Dixon, 2008). Most water-level measurements were made during a 5-day period; therefore, measurements do not represent a 'snapshot' of conditions at a specific time, nor do they necessarily coincide with the seasonal high water-level condition.

Ortiz, A. G.

2008-01-01

362

Potentiometric Surface of the Upper Floridan Aquifer, West-Central Florida, May 2007  

USGS Publications Warehouse

The Floridan aquifer system consists of the Upper and Lower Floridan aquifers separated by the middle confining unit. The middle confining unit and the Lower Floridan aquifer in west-central Florida generally contain highly mineralized water. The water-bearing units containing fresh water are herein referred to as the Upper Floridan aquifer. The Upper Floridan aquifer is the principal source of water in the Southwest Florida Water Management District and is used for major public supply, domestic use, irrigation, and brackish water desalination in coastal communities (Southwest Florida Water Management District, 2000). This map report shows the potentiometric surface of the Upper Floridan aquifer measured in May 2007. The potentiometric surface is an imaginary surface connecting points of equal altitude to which water will rise in tightly-cased wells that tap a confined aquifer system (Lohman, 1979). This map represents water-level conditions near the end of the dry season, when ground-water levels usually are at an annual low and withdrawals for agricultural use typically are high. The cumulative average rainfall of 41.21 inches for west-central Florida (from June 2006 through May 2007) was 11.63 inches below the historical cumulative average of 52.84 inches (Southwest Florida Water Management District, 2007). Historical cumulative averages are calculated from regional rainfall summary reports (1915 to most recent complete calendar year) and are updated monthly by the Southwest Florida Water Management District. This report, prepared by the U.S. Geological Survey in cooperation with the Southwest Florida Water Management District, is part of a semi-annual series of Upper Floridan aquifer potentiometric-surface map reports for west-central Florida. Potentiometric-surface maps have been prepared for January 1964, May 1969, May 1971, May 1973, May 1974, and for each May and September since 1975. Water-level data are collected in May and September each year to show the approximate annual low and high water-level conditions, respectively. Most of the water-level data for this map were collected by the U.S. Geological Survey during the period May 21-25, 2007. Supplemental water-level data were collected by other agencies and companies. A corresponding potentiometric-surface map was prepared for areas east and north of the Southwest Florida Water Management District boundary by the U.S. Geological Survey office in Orlando, Florida (Kinnaman and Dixon, 2007). Most water-level measurements were made during a 5-day period; therefore, measurements do not represent a 'snapshot' of conditions at a specific time, nor do they necessarily coincide with the seasonal low water-level condition.

Ortiz, A. G.

2008-01-01

363

Factors governing the assembly of cationic phospholipid-DNA complexes.  

PubMed Central

The interaction of DNA with a novel cationic phospholipid transfection reagent, 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine (EDOPC), was investigated by monitoring thermal effects, particle size, vesicle rupture, and lipid mixing. By isothermal titration calorimetry, the heat of interaction between large unilamellar EDOPC vesicles and plasmid DNA was endothermic at both physiological and low ionic strength, although the heat absorbed was slightly larger at the higher ionic strength. The energetic driving force for DNA-EDOPC association is thus an increase in entropy, presumably due to release of counterions and water. The estimated minimum entropy gain per released counterion was 1.4 cal/mole- degrees K (about 0.7 kT), consistent with previous theoretical predictions. All experimental approaches revealed significant differences in the DNA-lipid particle, depending upon whether complexes were formed by the addition of DNA to lipid or vice versa. When EDOPC vesicles were titrated with DNA at physiological ionic strength, particle size increased, vesicles ruptured, and membrane lipids became mixed as the amount of DNA was added up to a 1.6:1 (+:-) charge ratio. This charge ratio also corresponded to the calorimetric end point. In contrast, when lipid was added to DNA, vesicles remained separate and intact until a charge ratio of 1:1 (+:-) was exceeded. Under such conditions, the calorimetric end point was 3:1 (+:-). Thus it is clear that fundamental differences in DNA-cationic lipid complexes exist, depending upon their mode of formation. A model is proposed to explain the major differences between these two situations. Significant effects of ionic strength were observed; these are rationalized in terms of the model. The implications of the analysis are that considerable control can be exerted over the structure of the complex by exploiting vectorial preparation methods and manipulating ionic strength.

Kennedy, M T; Pozharski, E V; Rakhmanova, V A; MacDonald, R C

2000-01-01

364

Coulometric acid-base titration in nanoliter samples with glass and antimony electrodes.  

PubMed

A modification of the coulometric acid-base titration method is described for the measurement of titratable acid and ammonium in nanoliter samples. The main components consist of a pH-seeking device and a miniaturized antimony electrode system capable of delivering OH- ions at a known rate. The modifications include use of a cup-shaped pH-sensitive glass-membrane electrode for monitoring pH changes during titration and a new electronic titration circuit consisting of a high-impedance differential electrometer, a constant-current source, and an electronic integrating circuit. Details regarding the construction of the components of the titration system and practical aspects of its use are also provided. PMID:7058893

Karlmark, B; Jaeger, P; Fein, H; Giebisch, G

1982-01-01

365

New chemical titration proposed for potassium mud testing  

SciTech Connect

An accurate and easy-to-use procedure for measuring the potassium ion concentration in drilling and completion fluids has been developed and successfully used in Union Oil Co. of California's drilling operations. This volumetric analysis is based on the quantitative conversion of soluble sodium tetraphenylboron to the insoluble potassium tetraphenylboron and back titration with a quaternary ammonium salt in the presence of Titan yellow (Clayton yellow) indicator. This gives an easy-to-read color change endpoint from milky white to intense pink. The procedure described here is as fast as flame emission analysis and as accurate as the gravimetric analysis. This method has been used for several years in the fertilizer industry with success, but is new to drilling operations, at least in this revised form. This method, adapted from the potash industry, is easier and more accurate than other methods. Results compare favorably (within 3%) with flame emision or atomic absorption methods. The NaTPB method is proposed as a replacement for the method described in API RP 13B.

Zilch, H.E.

1984-01-01

366

Potentiometric surface of the upper Floridan Aquifer in the St. Johns River Water Management District and vicinity, Florida, May 1994  

USGS Publications Warehouse

This map depicts the potentiometric surface of the Upper Floridan aquifer in the St. Johns River Water Management District and vicinity for May 1994. The map is based on water-level measurements made at approximately 1,000 wells and several springs. Data on the map were contoured using 5-foot contour intervals in most areas. The potentiometric surface of this karstic aquifer generally reflects land surface topography. Potentiometric surface highs often correspond to topographic highs, which are areas of surficial recharge to the Upper Floridan aquifer. Springs within topographic lows along with areas of more diffuse upward leakage are natural zones of discharge. Municipal, agricultural, and industrial withdrawals have lowered the potentiometric surface in some areas. The potentiometric surface ranged from 125 feet above sea level in Polk County to 32 feet below sea level in Nassau County. Water levels in May 1994 generally were 0 to 3 feet lower than those measured in May 1993. Water levels in May 1994 in northeast Florida generally were 0 to 3 feet higher than in September 1993, except in the lower St. Johns River basin, where water levels were 0 to 4 feet lower than in September 1993. In the rest of the mapped area, water levels in May 1994 generally were 0 to 4 feet lower than those measured in September 1993.

Schiffer, D. M.; O'Reilly, A. M.; Phelps, G. G.; Bradner, L. A.; Halford, K. J.; Spechler, R. M.

1994-01-01

367

Synthetic cation-selective nanotube: Permeant cations chaperoned by anions  

NASA Astrophysics Data System (ADS)

The ability to design ion-selective, synthetic nanotubes which mimic biological ion channels may have significant implications for the future treatment of bacteria, diseases, and as ultrasensitive biosensors. We present the design of a synthetic nanotube made from carbon atoms that selectively allows monovalent cations to move across and rejects all anions. The cation-selective nanotube mimics some of the salient properties of biological ion channels. Before practical nanodevices are successfully fabricated it is vital that proof-of-concept computational studies are performed. With this in mind we use molecular and stochastic dynamics simulations to characterize the dynamics of ion permeation across a single-walled (10, 10), 36 A? long, carbon nanotube terminated with carboxylic acid with an effective radius of 5.08 A?. Although cations encounter a high energy barrier of 7 kT, its height is drastically reduced by a chloride ion in the nanotube. The presence of a chloride ion near the pore entrance thus enables a cation to enter the pore and, once in the pore, it is chaperoned by the resident counterion across the narrow pore. The moment the chaperoned cation transits the pore, the counterion moves back to the entrance to ferry another ion. The synthetic nanotube has a high sodium conductance of 124 pS and shows linear current-voltage and current-concentration profiles. The cation-anion selectivity ratio ranges from 8 to 25, depending on the ionic concentrations in the reservoirs.

Hilder, Tamsyn A.; Gordon, Dan; Chung, Shin-Ho

2011-01-01

368

Rapid baculovirus titration based on regulatable green fluorescent protein expression in mammalian cells.  

PubMed

Baculovirus is a promising gene delivery vector and can be titrated by constitutive EGFP expression in HeLa cells, which, however, might interfere with target transgene expression and impart cytotoxicity. Here we constructed Bac-ME accommodating egfp under the inducible metallothionein promoter and Bac-MECB harboring an additional BMP-2 gene. Bac-ME effectively transduced HeLa cells with minimal leaky expression, but expressed EGFP robustly upon induction with ZnSO(4), hence allowing for virus titration by transducing HeLa cells with serially diluted virus, subsequent ZnSO(4) induction and flow cytometry analysis of EGFP-positive cells. The titration protocol enabled the generation of discernable titration curves, determination of transducing titers, and discrimination of the transducing abilities of different virus batches. After titration, cell transduction with pre-determined Bac-ME dose revealed consistent transduction efficiency dependence on the dose, regardless of virus batch and cell type. Bac-MECB was similarly titrated by inducible EGFP expression and used to transduce de-differentiated articular chondrocytes without EGFP induction. BMP-2 expression was proportional to the Bac-MECB dose and promoted cartilage-specific matrix synthesis, implicating the potential of Bac-MECB in restoring chondrocyte differentiation. These data confirmed that regulatable EGFP expression enabled rapid, reliable baculovirus titration without interference with subsequent applications. PMID:22112765

Lo, Wen-Hsin; Chen, Chi-Yuan; Yeh, Chia-Ni; Lin, Chin-Yu; Hu, Yu-Chen

2010-08-21

369

A naphthyl analog of the aminostyryl pyridinium class of potentiometric membrane dyes shows consistent sensitivity in a variety of tissue, cell, and model membrane preparations  

Microsoft Academic Search

Summary  The fast potentiometric indicator di-4-ANEPPS is examined in four different preparations: lipid vesicles, red blood cells, squid giant axon, and guinea pig heart. The dye gives consistent potentiometric responses in each of these systems, although some of the detailed behavior varies. In lipid vesicles, the dye displays an increase in fluorescence combined with a red shift of the excitation spectrum

Leslie M. Loewt; Lawrence B. Cohenw; James Dix; Eric N. Fluhler; Valerie Montanat; Guy Salama; Wu Jian-youngw

1992-01-01

370

Modeling and optimization of the bi-substrate peroxidase-enzyme catalyzed potentiometric assay of hydrogen peroxide by response surface methodology with a central composite rotatable design  

Microsoft Academic Search

In view of the great importance of determination of hydrogen peroxide in many chemical, biological, clinical, environmental processes, and the attractive operational simplicity of potentiometric approach for the enzymatic assay, after preliminary optimization, the efficient response surface methodology (RSM) with a central composite rotatable design (CCRD), was used for modeling and optimization of the initial-rate potentiometric method of HRP enzyme

Farzad Deyhimi; Faezeh Nami

2011-01-01

371

Periodate Titration of Fe(II) in Acid Aqueous Solutions: An Environmentally Friendly Redox Reaction for the Undergraduate Laboratory  

Microsoft Academic Search

An environmentally friendly redox laboratory for the determination of Fe(II) in an acid aqueous medium is presented. This laboratory exercise is an appropriate substitute for the traditional dichromate titration, which is environmentally problematic. This titration method uses the periodate ion as the oxidizing agent and yields results which are as accurate as the dichromate titration. Student success rate in quantitative

THOMAS G. DRUMMOND; WILLIAM L. LOCKHART; SPENCER J. SLATTERY; FAROOQ A. KHAN; ANDREW J. LEAVITT

1997-01-01

372

Integrated potentiometric detector for use in chip-based flow cells  

PubMed

A new kind of potentiometric chip sensor for ion-selective electrodes (ISE) based on a solvent polymeric membrane is described. The chip sensor is designed to trap the organic cocktail inside the chip and to permit sample solution to flow past the membrane. The design allows the sensor to overcome technical problems of ruggedness and would therefore be ideal for industrial processes. The sensor performance for a Ba2+-ISE membrane based on a Vogtle ionophore showed electrochemical behavior similar to that observed in conventional electrodes and microelectrode arrangements. PMID:10905321

Tantra; Manz

2000-07-01

373

Study of CO 2 electrodes in open devices of potentiometric sensors  

Microsoft Academic Search

Potentiometric CO2 sensors in open devices with NASICON as solid electrolyte were tested in the temperature range 150–500 °C and at partial pressures between 10?6 and 0.1 atm in air. The sensors were built with sodium titanate and La1?xSrXMnO3±? (LSM) mixtures as oxygen reference electrode and Na2CO3–BaCO3 or Na2CO3–SrCO3 mixed with gold as measuring electrodes. The CO2 electrode reaction is

Joel Ram??rez-Salgado; Pierre Fabry

2003-01-01

374

Feasibility of potentiometric oxygen gas sensor based on perovskite and sodium titanate measuring electrode  

Microsoft Academic Search

A new solid potentiometric sensor for the oxygen gas detection using NASICON as solid electrolyte is proposed and tested in the range 300–700°C for a feasibility study. The measuring electrode is a mixture of Na2Ti3O7–Na2Ti6O13 and La1?xSrxMnO3±? (LSM) as mixed electronic and ionic conductors. A system based on Ni-NiO\\/Na2Ti3O7–Na2Ti6O13 is used as solid internal reference. A linear relationship was observed

J. Ram??rez-Salgado; P. Fabry

2002-01-01

375

Long-term stability of potentiometric CO 2 sensors based on Nasicon as a solid electrolyte  

Microsoft Academic Search

Five solid-state potentiometric CO2 sensors of the type: CO2, O2, Ag, M2CO3–BaCO3 |Nasicon| X, Pt, O2 (where M=Li or Na, X—Na2O activity buffer) were investigated. The effects of electrode composition and operating temperature on long-term performance of sensors were determined. It was found that the sensors with Na2Ti6O13\\/Na2Ti3O7 reference electrode show stable signal during 1000h. No effect of the sensing

P. Pasierb; S. Komornicki; S. Kozi?ski; R. Gajerski; M. R

2004-01-01

376

Ionselective light-addressable potentiometric sensor (LAPS) with chalcogenide thin film prepared by pulsed laser deposition  

Microsoft Academic Search

Pb–Ag–As–I–S chalcogenide glass was deposited on the surface of a light-addressable potentiometric sensor (LAPS) by means of the pulsed laser beam deposition (PLD) technique. The deposited layer worked as a Pb2+-ion-sensitive transducer, and the sensor showed Nernstian response with a sensitivity of 29±1mV\\/decade. The detection limit of the sensor for Pb2+-ions was 1×10?6mol\\/l. The response time does not exceed 50s

Y. Mourzina; T. Yoshinobu; J. Schubert; H. Lüth; H. Iwasaki; M. J. Schöning

2001-01-01

377

Light Addressable Potentiometric Sensor with Fluorine-Terminated Hafnium Oxide Layer for Sodium Detection  

NASA Astrophysics Data System (ADS)

In this study, post-CF4 plasma surface treatment of light addressable potentiometric sensor (LAPS) with a HfO2-sensing membrane was carried out. pH sensitivity decreased but pNa sensitivity increased with fluorine incorporation. The highest pNa sensitivity was 31.8 mV/pNa, which was optimized with 3 min post CF4 plasma treatment. The results showed a high possibility for sensing sodium ions using an inorganic-sensing membrane and a fabrication process. Moreover, on the basis of the analysis of atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) spectra, a sensing mechanism was developed.

Cheng-En Lue,; Chao-Sung Lai,; Hsin-Yu Chen,; Chia-Ming Yang,

2010-04-01

378

Potentiometric study of polyaniline film synthesized with various dopants and composite-dopant: A comparative study  

Microsoft Academic Search

The potentiometric study of polyaniline (PANI) film synthesized with dopants viz. polyvinyl sulfonic acid (PVS),p-toluene sulfonic acid (p\\u000a TS), dodecyl benzene sulfonic acid (DBS) and composite-dopants viz. PVS-p\\u000a TS and PVS-DBS, has been carried out. The synthesized PANI films were characterized by electrochemical technique, UV-visible\\u000a spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and conductivity measurement.\\u000a It was

P. D. Gaikwad; D. J. Shirale; V. K. Gade; P. A. Savale; K. P. Kakde; H. J. Kharat; M. D. Shirsat

2006-01-01

379

Electronic tongue for the determination of alkaline ions using a screen-printed potentiometric sensor array  

Microsoft Academic Search

.  A disposable all-solid-state planar-type potentiometric electronic tongue has been developed with a five-sensor array screen-printed\\u000a on a polymeric substrate. The fabrication method enables simple and reproducible mass-production of low-cost electronic tongue\\u000a systems, since the sensors showed good reproducibility (0.96% RSD), repeatability (0.58% RSD) and lifetime (8% decrease of\\u000a sensitivity after 37 days in solution). The system was used for the

Manuel Gutiérrez; Victor M. Moo; Salvador Alegret; Lorenzo Leija; Pablo R. Hernández; Roberto Muñoz; Manel del Valle

2008-01-01

380

Determination of the Oxidative Redox Capacity of Aquifer Sediment Material By Spectrochemical Coulometric Titration.  

National Technical Information Service (NTIS)

Methodology was developed for determination of the oxidative redox capacity of aquifer sediment material by the method of spectroelectrochemical coulometric titration. This method involves the measurement of absorbance of sediment particles slurries at th...

J. L. Anderson M. C. Delgado

1996-01-01

381

Geochemical modeling of reactions and partitioning of trace metals and radionuclides during titration of contaminated acidic sediments.  

PubMed

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 studywas 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 SO4(2-) for contaminated sediments indicated close agreement suggesting that the model could potentially be used to predictthe acid-base behavior of the sediment-solution system under variable pH conditions. PMID:19031894

Zhang, Fan; Luo, Wensui; Parker, Jack C; Spalding, Brian P; Brooks, Scott C; Watson, David B; Jardine, Philip M; Gu, Baohua

2008-11-01

382

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

383

Recent investigations permitting a new interpretation of the results of the conventional titration of gastric juice  

Microsoft Academic Search

Conclusions  Titration of gastric juice with a dilute alkali to the lemon yellow end-point of Töpfer’s indicator measures not only the\\u000a free hydrochloric acid but the acid combined with the gastric proteins (chlorides and phosphates) and also free phosphoric\\u000a acid. This fact is of importance in interpreting the results of the smaller titration figures (i. e., below 8–10 c.c.) for\\u000a they

Lay Martin

1934-01-01

384

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

385

Coulometric Determination of Protein Nitrogen Application to Direct Titration of Kjeldahl Digests  

Microsoft Academic Search

A coulometric method is described for the determination of ammonia resulting from micro-Kjeldahl digestion of protein samples. The method has been applied to the direct titration of the ammonia in the digests. Routine titration of the ammonia resulting from lO-?sl. serum samples is described; the method has been applied to 1-JLI.samples. Results are compared with standard macro- and micro-Kjeldahl procedures.

Gary D. Christian; Edward C. Knoblock; William C. Purdy

386

A Rapid Air Titration Method for Determining SO2 Concentration in Inhalation Chambers  

Microsoft Academic Search

A rapid air titration method for determining SO2 concentration in inhalation chambers has been validated using the pararosaniline-formaldehyde (PRA) method of West and Gaeke. This air-titration (iodate) method is an adaptation of iodometric methods using a starch indicator. Potassium iodate and an excess of potassium iodide are used in the reaction. Sampling is completed in ten minutes or less and

EILEEN A. SNYDER; E. D. PALMES

1985-01-01

387

ANALYSES BY CONDUCTOMETRIC TITRATION OF CHLORIDES FROM WASTEWATERS THAT CONTAINS HEAVY METALS  

Microsoft Academic Search

SUMMARY The Romanian legislation trough its standards recommend to analyze the chlorides from wastewaters using the method of standard Mohr titration. A very facile and selective method is proposed for fast determination of chloride from wastewaters resulted from galvanization processes, by conductometric titration using AgNO3. The method allows to analyze the chlorides over the range 177.5 ÷ 17750 mg Cl-\\/l

Laura BULGARIU; Brindusa ROBU; Doina BILBA; M. MACOVEANU

388

A New and Sharp Ternary Indicator System for Argentometric Titration of Microamounts of Iodide  

Microsoft Academic Search

.  ?A ternary indicator system, Cadion 1B-silver ion-emulsifier octylphenyl polyglycol ether, for visual and direct titration\\u000a of iodide ion with silver nitrate (as the titrant) is described. The advantages of the method are as follows: (1) when the\\u000a titration reaches the equivalence point, the color of the resulting solution sharply changes from pure yellow to orange and\\u000a the solution remains transparent

Guo-Zhen Fang; Shang-Fen Gao

2001-01-01

389

Effects of cultivation conditions on acid-base titration properties of Shewanella putrefaciens  

Microsoft Academic Search

Acid-base titrations were conducted on pure strain laboratory cultures of the Gram-negative, facultatively aerobic bacterium Shewanella putrefaciens, cultivated under a range of conditions. Bacteria used in acid-base titrations were cultivated for periods of 24 to 100 h (exponential growth phase to late stationary phase), in varying media compositions (rich to minimal), and under aerobic and anaerobic conditions. In addition, two

Johnson R. Haas

2004-01-01

390

DETERMINATION OF TECHNETIUM BY CONTROLLED-POTENTIAL COULOMETRIC TITRATION IN BUFFERED SODIUM TRIPOLYPHOSPHATE MEDIUM  

Microsoft Academic Search

A controlled-potential coulometric method for the determination of Tc ; was developed whereby Tc(VII) is titrated in an acetate-buffered (pH 4.7) ; solution of sodium tripolyphosphate at a potential of --0.70 volt vs S.C.E. In ; the range from about 0.5 to 5 mg of Tc(VII) titrated, the relative error of the ; method is about 450 deg C in

A. A. Terry; H. E. Zittel

1963-01-01

391

Efficacy and Tolerability of Rosuvastatin and Atorvastatin when Force-Titrated in Patients with Primary Hypercholesterolemia  

Microsoft Academic Search

Background: Patients at high risk of cardiovascular disease frequently fail to reach recommended low-density lipoprotein cholesterol (LDL-C) goals, partly because statin doses are not titrated to optimal effect. The ECLIPSE study was designed to compare the efficacy and safety of force-titrated treatment with rosuvastatin (10–40 mg) with that of atorvastatin (10–80 mg) in high-risk patients with hypercholesterolemia. Methods: In this

Ole Faergeman; Laurie Hill; Eberhard Windler; Olov Wiklund; Roland Asmar; Emma Duffield; Froukje Sosef

2008-01-01

392

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

393

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

394

A biomimetic potentiometric sensor based on molecularly imprinted polymer for the determination of memantine in tablets.  

PubMed

Memantine hydrochloride is one of the first novel class medications for treatment of Alzheimer's disease. In this work, a biomimetic potentiometric sensor, based on a non-covalent imprinted polymer, was fabricated for the recognition and determination of memantine in pure drug and tablet pharmaceutical form. The molecularly imprinted polymer was synthesized by precipitation polymerization, using memantine hydrochloride as a template molecule, methacrylic acid as a functional monomer, and ethylene glycol dimethacrylate as a cross-linking agent. The sensor was developed by dispersing the memantine imprinted polymer particles in dibutyl sebacate plasticizer and embedding in poly(vinyl chloride) matrix. The wide linear range (10(-5) -10(-1) ?M), with a near Nernstian response of 57.4?mV/decade, a limit of detection 6.0?×?10(-6) ?M, fast response time (~15?s) and a satisfactory long-term stability (4?months) are characterizations of the proposed sensor. The sensor showed a high selectivity and a sensitive response to the template in aqueous system. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode. It was used as indicator electrode in potentiometric determination of memantine in pharmaceutical formulations. PMID:22514137

Arvand, Majid; Samie, Hedyeh Asadi

2012-04-18

395

Pincher ferrocene-derived cation carboxylate ion pairs in aqueous DMSO.  

PubMed

Pincher cationic ferrocene hosts for carboxylate ion guests were synthesized and the binding constants were determined by NMR or UV-Vis titrations. These (di)cationic hosts form tight complexes with benzoate or acetate even in competitive aqueous DMSO solvent. A bis(acylguanidinium) ferrocene dication achieves a remarkable Ka of ~10(6) M(-1) to acetate in 9 : 1 DMSO-H2O and a Ka of 850 M(-1) in neat D2O, one of the highest association constants known for a carboxylate complex exploiting only electrostatic interactions in neat water. DFT computations of the binding enthalpy are in good agreement with the experimentally determined association constants. The ferrocene backbone used in these pincher complexes may prove to be a useful semi-flexible scaffold for redox detectable/switchable self-assemblies in aqueous solutions. PMID:23896645

Beck, Christie L; Berg, Stephen A; Winter, Arthur H

2013-09-21

396

Potentiometric surface of the Upper Floridan aquifer, west-central Florida, May 2005  

USGS Publications Warehouse

The Floridan aquifer system consists of the Upper and Lower Floridan aquifers separated by the middle confining unit. The middle confining unit and the Lower Floridan aquifer in west-central Florida generally contain highly mineralized water. The water-bearing units containing freshwater are herein referred to as the Upper Floridan aquifer. The Upper Floridan aquifer is a highly productive aquifer and supplies more than 10 times the amount of water pumped from either the surficial aquifer system or the intermediate aquifer system in most of the study area (Duerr and others, 1988). This map report shows the potentiometric surface of the Upper Floridan aquifer measured in May 2005. The potentiometric surface is an imaginary surface connecting points of equal altitude to which water will rise in a tightly cased well that taps a confined aquifer system (Lohman, 1979). This map represents water-level conditions near the end of the dry season, when ground-water levels usually are at an annual low and withdrawals for agricultural use typically are high. The cumulative average rainfall of 67.27 inches for west-central Florida (from June 2004 through May 2005) was 14.20 inches above the historical cumulative average of 53.07 inches (Southwest Florida Water Management District (SWFWMD), 2005). The above average precipitation is attributed to the active hurrican season for Florida in 2004. Historical cumulative averages are calculated from regional rainfall summary reports (1915 to the most recent completed calendar year) and are updated monthly by the SWFWMD. This report, prepared by the U.S. Geological Survey (USGS) in cooperation with the SWFWMD, is part of a semiannual series of Upper Floridan aquifer potentiometric-surface map reports for west-central Florida. Potentiometric-surface maps have been prepared for January 1964, May 1969, May 1971, May 1973, May 1974, and for each May and September since 1975. Water-level data are collected in May and September each year to show the approximate annual low and high water-level conditions, respectively. Most of the water-level data for this map were collected by the USGS during May 23-27, 2005. Supplemental water-level data were collected by other agencies and companies. A corresponding potentiometric-surface map was prepared for areas east and north of the SWFWMD boundary by the USGS office in Altamonte Springs, Florida (Kinnaman, 2006). Most water-level measurements were made during a 5-day period; therefore, measurements do not represent a 'snapshot' of conditions at a specific time, nor do they necessarily coincide with the seasonal low water-level condition. Water levels in about 19 percent of the wells measured in May 2005 were lower than the May 2004 water levels (Blanchard and others, 2004). Data from 409 wells indicate that the May 2005 water levels ranged from about 5 feet below to about 18 feet above the May 2004 water levels (fig. 1). The largest water-level declines occurred in southwestern Hernando County, northeastern Hillsborough County, and parts of Hillsborough, Sumter, and Sarasota Counties. The largest water-level rises occurred in southeastern Hillsborough County, eastern Manatee County, and western Hardee County (fig. 1). Water levels in about 95 percent of the wells measured in May 2005 were lower than the September 2004 water levels (Blanchard and Seidenfeld, 2005). Data from 405 wells indicate that the May 2005 water levels ranged from about 22 feet below to 14 feet above the September 2004 water levels. The largest water-level decline was in east-central Manatee County and the largest water-level rise was in central Sarasota County.

Ortiz, A. G.; Blanchard, R. A.

2006-01-01

397

Influence of the cavity size of water-soluble cryptophanes on their binding properties for cesium and thallium cations.  

PubMed

The binding properties of water-soluble cryptophane 1 toward cesium and thallium cations, in basic solution, have recently been reported. In this Article, we show that water-soluble cryptophane-222 (2), cryptophane-223 (3), and cryptophane-233 (4), bearing zero, one, and two propylenedioxy linkers, respectively, also efficiently bind these two cations under similar experimental conditions. Their binding properties are thoroughly studied by (133)Cs and (205)Tl NMR spectroscopy, while the binding constants are determined by isothermal titration calorimetry (ITC) experiments under various experimental conditions. Complexation of cesium and thallium is also evidenced by electronic circular dichroism (ECD) using the enantiopure MM-2 compound. This study reveals that the cavity size of the cryptophane is not the main parameter to observe efficient binding. In contrast, the number of phenolate moieties surrounding the cryptophane backbone seems to be pivotal for the complexation of these two cations. These results are important in the field of detoxification. PMID:24053547

Brotin, Thierry; Goncalves, Sylvie; Berthault, Patrick; Cavagnat, Dominique; Buffeteau, Thierry

2013-10-07

398

Electrometric method for the determination of the nitrogen content in metals and ferroalloys  

SciTech Connect

To determine cationic and nonionogenic surfactants in a mixture, the authors used potentiometric titration of aqueous solutions of the surfactants with 0.01M solution of tetraphenylborate. The indicator electrodes were polyvinyl chloride membrane electrodes with electroactive substances -- the cetylpyridinium salt of dodecylbenzenesulfonic acid, recommended for the determination of ionic surfactants and barium (II), respectively.

Agafonov, P.F.; Zueva, V.L.

1985-11-01

399

Long-range nature of the interactions between titratable groups in Bacillus agaradhaerens family 11 xylanase: pH titration of B. agaradhaerens xylanase.  

PubMed

Xylanase from Bacillus agaradhaerens belongs to a large group of glycosyl hydrolases which catalyze the degradation of xylan. The protonation behavior of titratable groups of the uniformly (15)N- and (13)C-labeled xylanase was investigated by multinuclear NMR spectroscopy. A total of 224 chemical shift titration curves corresponding to (1)H, (13)C, and (15)N resonances revealed pK(a) values for all aspartic and glutamic acid residues, as well as for the C-terminal carboxylate and histidine residues. Most of the titratable groups exhibit a complex titration behavior, which is most likely due to the mutual interactions with other neighboring groups or due to an unusual local microenvironment. Subsite -1 containing the catalytic dyad shows a long-range interaction over 9 A with Asp21 via two hydrogen bonds with Asn45 as the mediator. This result illuminates the pivotal role of the conserved position 45 among family 11 endoxylanases, determining an alkaline pH optimum by asparagine residues or an acidic pH optimum by an aspartate. The asymmetric interactions of neighboring tryptophan side chains with respect to the catalytic dyad can be comprehended as a result of hydrogen bonding and aromatic stacking. Most of the chemical shift-pH profiles of the backbone amides exhibit biphasic behavior with two distinct inflection points, which correspond to the pK(a) values of the nearby acidic side chains. However, the alternation of both positive and negative slopes of individual amide titration curves is interpreted as a consequence of a simultaneous reorganization of side chain conformational space at pH approximately 6 and/or an overall change in the hydrogen network in the substrate binding cleft. PMID:15134456

Betz, Marco; Löhr, Frank; Wienk, Hans; Rüterjans, Heinz

2004-05-18

400

Simulated effects of ground-water development on potentiometric surface of the Floridan Aquifer, west-central Florida  

USGS Publications Warehouse

A digital model of two-dimensional ground-water flow was used to predict changes in the potentiometric surface of the Floridan aquifer, 1976 to 2000, in a 5,938-square-mile area of west-central Florida. In 1975, ground water withdrawn from the Floridan aquifer for irrigation, phosphate mines, other industries, and municipal supplies averaged about 649 million gallons per day. Rates are projected to increase to about 840 million gallons per day by 2000. The model was calibrated under steady-state and transient conditions. Input parameters included transmissivity and storage coefficient of the Floridan aquifer; thickness, vertical hydraulic conductivity, and storage coefficient of the upper confining bed; altitudes of the water table and potentiometric surface; and ground-water withdrawals. Simulation of May 1976 to May 2000, using projected combined pumping rates for municipal supplies, irrigation, and industry (including existing and proposed phosphate mines), resulted in a rise in the potentiometric surface of about 10 feet in Polk County, and a decline of about 35 feet in parts of Manatee and Hardee Counties. The lowest predicted potentiometric level was about 30 feet below sea level. Predicted declines for November 1976 to October 2000 were generally 5 to 10 feet less than those for May 1976 to May 2000. (USGS)

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

1982-01-01

401

Integration of bienzymatic disaccharide sensors for simultaneous determination of disaccharides by means of light addressable potentiometric sensor  

Microsoft Academic Search

Three saccharides such as sucrose, maltose and glucose were simultaneously determined by the use of the light addressable potentiometric sensor (LAPS). One-chip integration of three saccharide sensors was performed by means of a glucose sensor using glucokinase. By the addition of oligosaccharide hydrolases such as invertase and ?-d-glucosidase to the glucose sensors, the disaccharide concentrations were determined by variation of

Kazuhito Aoki; Hidekazu Uchida; Teruaki Katsube; Yoshihiro Ishimaru; Takeaki Iida

2002-01-01

402

A novel light-addressable potentiometric sensors set-up with LCD projector as scanning light source  

Microsoft Academic Search

In a typical set-up of light-addressable potentiometric sensor (LAPS), the individual sensing parts of the photosensitive semiconductor chip are addressed by modulated light beam such as laser beam. Although the laser can be executed with precision, the relative equipment is complex and expensive. In this work, a novel approach of utilizing Liquid Crystal Display (LCD) projector as a programmable modulated

Yen-Heng Lin; Anirban Das; Kai-Siang Ho; Chao-Sung Lai

2011-01-01

403

Potentiometric surface of the Wilcox-Carrizo Aquifer; Bienville, Red River, and northern Natchitoches, and southern Webster parishes, Louisiana  

USGS Publications Warehouse

The potentiometric surface of the Wilcox-Carrizo aquifer in central northwestern Louisiana is shown by contours using data collected from 1960 to 1980. The aquifer is not affected by regional water-level declines as no large pumping centers have been developed. Seasonal water-level fluctuations in wells are generally less than 10 feet annually. (USGS)

Ryals, G. N.

1981-01-01

404

Potentiometric map of the Eutaw-McShan Aquifer in northeastern Mississippi, September, October, and November 1978  

USGS Publications Warehouse

This potentiometric map of the Eutaw-McShan aquifer in northeastern Mississippi is the third 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. From its outcrop area the Eutaw-McShan aquifer dips about 30 feet per mile to the west and southwest. Thickness of the aquifer commonly is between 200 and 300 feet in most of the area, and commonly about one-half this thickness consists of sand. In the outcrop area the potentiometric surface is strongly affected by recharge from precipitation, topography, and drainage of the aquifer by streams. The potentiometric surface of the aquifer slopes generally to the west away from the area of outcrop and it is strongly affected by large ground-water withdrawals at or near Tupelo, Aberdeen, and West Point. Historically, water levels in or near the outcrop of the Eutaw-McShan aquifer have shown little or no long-term changes. Withdrawals of water by wells from the downdip area have caused long-term water-level declines of 1 to 2 feet per year in much of the confined part of the aquifer. Water-level declines during recent years in several observation wells in Lee County ranged from 2 to 9 feet per year. One hydrograph in Clay County that is near the center of the depression in the potentiometric surface at West Point shows about 5 feet per year of water-level decline since 1972. (USGS)

Wasson, B. E.

1980-01-01

405

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

2013-01-22

406

Cation affinity numbers of Lewis bases  

PubMed Central

Summary Using selected theoretical methods the affinity of a large range of Lewis bases towards model cations has been quantified. The range of model cations includes the methyl cation as the smallest carbon-centered electrophile, the benzhydryl and trityl cations as models for electrophilic substrates encountered in Lewis base-catalyzed synthetic procedures, and the acetyl cation as a substrate model for acyl-transfer reactions. Affinities towards these cationic electrophiles are complemented by data for Lewis-base addition to Michael acceptors as prototypical neutral electrophiles.

Lindner, Christoph; Tandon, Raman; Maryasin, Boris; Larionov, Evgeny

2012-01-01

407

Cationic surfactants based on ferrocene  

SciTech Connect

Quaternary ammonium salts based on ferrocene were synthesized and their surface active properties were studied as potential cationic surfactants and for uses including antiknock compounds. The salts were halide and nitrate derivatives of dimethylferrocenylmethylammonium and were prepared by aminomethylation of ferrocene. Chemical reaction yields, melting points, surface tension isotherms, and other characteristics were assessed.

Pankratov, V.A.; Kucherova, N.L.; Abramzon, A.A.

1988-07-20

408

A simple-potentiometric method for determination of acid and alkaline phosphatase enzymes in biological fluids and dairy products using a nitrophenylphosphate plastic membrane sensor.  

PubMed

A novel poly(vinyl chloride) matrix membrane sensor responsive to 4-nitrophenylphosphate (4-NPP) substrate is described, characterized and used for the potentiometric assay of acid (ACP) and alkaline (ALP) phosphatase enzymes. The sensor is based on the use of the ion-association complex of 4-NPP anion with nickel(II)-bathophenanthroline cation as an electroactive material and nitrophenyloctyl ether (NPOE) as a solvent mediator. The sensor displays good selectivity and stability and demonstrates a near-Nernstian response for 4-NPP over the concentration range 9.6x10(-6) to 1.0x10(-2) M with an anionic slope of 28.6+/-0.3 mV decade(-1) and a detection limit of 6.3x10(-6) M over the pH range 4.5-10. The sensor is used to measure the decrease of a fixed concentration of 4-NPP substrate as a function of acid and alkaline phosphatase enzyme activities at optimized conditions of pH and temperature. A linear relationship between the initial rate of 4-NPP substrate hydrolysis and enzyme activity holds over 0.05-3.0 and 0.03-3.4 IU L(-1) of ACP and ALP enzymes, respectively. Validation of the method by measuring the lower detection limit, range, accuracy, precision, within-day repeatability and between-day-variability reveals good performance characteristics of the proposed sensor. The sensor is used for the determination of acid and alkaline phosphatase enzyme activities in biological fluids of some patients suffering from alcoholic cirrhosis, acute myelocytic leukemia, pre-eclampsia and prostatic cancer. The sensor is also utilized for assessment of alkaline phosphatase enzyme in milk and dairy products. The results obtained agree fairly well with data obtained by the standard spectrophotometric methods. PMID:19362623

Hassan, Saad S M; Sayour, Hossam E M; Kamel, Ayman H

2009-03-20

409

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

410

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

SciTech Connect

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; Valle, Manel del [Sensors and Biosensors Group, Chemistry Dept., Universitat Autonoma de Barcelona, Edifici Cn, 08193 Bellaterra, Barcelona (Spain); Legin, Andrey [Chemistry Dept, St. Petersburg University, Universitetskaya nab. 7/9, 199034 St. Petersburg (Russian Federation)

2009-05-23

411

Mediated xanthine oxidase potentiometric biosensors for hypoxanthine based on ferrocene carboxylic acid modified electrode.  

PubMed

A potentiometric enzyme electrode for detection of hypoxanthine (Hx) in fish meat is described. The sensor was developed by entrapment of xanthine oxidase (XOD) and ferrocene carboxylic acid (Fc) into polypyrrole (PPy) film during galvanostatic polymerisation film formation. The responses for Hx were obtained in 0-05 M phosphate buffer (pH 7.1) at 0.0 mV vs Ag/AgCl (3M KCl). The optimum condition for the formation of PPy-XOD-Fc film include 0.4M PPy, 6.2U/mL XOD, 40 mM Fc, polymerisation time of 200 s and applied current density of 0-5 mA cm(-2). The sensor provides a linear response to Hx in concentration range of 5-20 ?M, (r=0.998) and was successfully used for determination of Hx in fish. PMID:22980900

Lawal, Abdulazeez T; Adeloju, Samuel B

2012-07-21

412

Potentiometric stripping analysis (PSA) for monitoring of antimony in samples of vegetation from a mining area.  

PubMed

A potentiometric stripping analysis (PSA) method has been developed and checked for the fast and reliable determination of antimony in vegetation samples of Cistus ladanifer from a mining area in Badajoz, Southwest Spain. The method, modified from previous PSA methods for Sb in environmental samples, is based on dry ashing of the homogenized leaves, dissolution in hydrochloric acid, and PSA analysis on a mercury film plated on to a glassy carbon disk electrode. The influence of experimental variables such as the deposition potential, the deposition time, the signal stability and the calibration parameters, has been investigated. The method has been compared with an independent technique (instrumental neutron activation analysis) by analysis of standards and reference materials and comparison of the results. As a result of automation of the PSA equipment, the proposed method enables unattended analysis of 20 digested samples in a total time of 2 h, thus providing a useful tool for Sb monitoring of a large number of samples. PMID:11495070

Toro Gordillo, M C; Pinilla Gil, E; Rodríguez González, M A; Murciego Murciego, A; Ostapczuk, P

2001-06-01

413

Metal complexes of luteinizing hormone-releasing hormone (LHRH). Potentiometric and spectroscopic studies  

SciTech Connect

The results are reported of a potentiometric and spectroscopic study of the H+, Cu2+, and Ni2+ complexes of luteinizing hormone-releasing hormone (LHRH, HL) at 25 degrees C and an ionic strength 0.10 mol dm-3 (KNO3), since there is much evidence that the in vivo release of LHRH is influenced by the concentration of copper ions. With Cu2+ the hormone has been shown to behave similarly to the thyrotropin releasing factor, forming a very stable (CuH-1L) complex involving coordination of three nitrogen donors: the Nim atom of the imidazole side chain and the two amido-N atoms of the pyroglutamylhistidyl unit. With Ni2+, coordination proceeds differently to give four nitrogen coordination.

Gerega, K.; Kozlowski, H.; Masiukiewicz, E.; Pettit, L.D.; Pyburn, S.; Rzeszotarska, B.

1988-05-01

414

Development of a tubular fluoride potentiometric detector for flow analysis: evaluation and analytical applications.  

PubMed

In this work a construction procedure for tubular fluoride electrode to be used in flow systems is outlined. The electrode was constructed from a commercially available, LaF3 single crystal. Principal advantages of the flow detector presented include simplicity of construction, robustness, durability, low cost and easy coupling into any point of a flow manifold. Evaluation of the intrinsic working characteristics of the potentiometric detector in a low dispersion manifold is presented with respect to analytical and dynamic parameters. The constructed detector has similar working characteristics to those of the conventional fluoride electrodes, namely the detection limit, lower limit of linear response and operational pH range. The analytical usefulness of the constructed device was assessed in a flow system developed for fluoride determination in toothpaste, tablet, collutory and water samples for which the reference procedures suggest the determination of fluoride ion with a conventional ion selective electrode. PMID:17386576

Santos, João Rodrigo; Lapa, R A S; Lima, José L F C

2006-10-19

415

Highly efficient potentiometric glucose biosensor based on functionalized InN quantum dots  

NASA Astrophysics Data System (ADS)

We present a fast, highly sensitive, and efficient potentiometric glucose biosensor based on functionalized InN quantum-dots (QDs). The InN QDs are grown by molecular beam epitaxy. The InN QDs are bio-chemically functionalized through physical adsorption of glucose oxidase (GOD). GOD enzyme-coated InN QDs based biosensor exhibits excellent linear glucose concentration dependent electrochemical response against an Ag/AgCl reference electrode over a wide logarithmic glucose concentration range (1 × 10-5 M to 1 × 10-2 M) with a high sensitivity of 80 mV/decade. It exhibits a fast response time of less than 2 s with good stability and reusability and shows negligible response to common interferents such as ascorbic acid and uric acid. The fabricated biosensor has full potential to be an attractive candidate for blood sugar concentration detection in clinical diagnoses.

Alvi, N. H.; Soto Rodriguez, P. E. D.; Gómez, V. J.; Kumar, Praveen; Amin, G.; Nur, O.; Willander, M.; Nötzel, R.

2012-10-01

416

The Study on Bionic Olfactory Neurochip Based on Light-addressable Potentiometric Sensor.  

PubMed

Olfactory system can distinguish thousands of odors. In order to utilize biological olfactory neurons as sensitive material of electronic nose, this article reports an olfactory neurochip as real bionic technique for odorants detection. Effective cultures of olfactory receptor neurons and olfactory bulb cells on the chip have been achieved. Using light-addressable potentiometric sensor (LAPS) as sensing chip to monitor extracellular potential of the neurons, we tested the response under stimulations of the odorants or neurotransmitters, such as acetic acid and glutamic acid. The results demonstrate that this kind of the LAPS and olfactory neurons hybrid system is sensitive to environmental changes, which has potential to be used as a novel bioelectrical nose for detecting odors. PMID:17281331

Liu, Qingjun; Xu, Ying; Cai, Hua; Qin, Lifeng; Ye, Xuesong; Li, Rong; Wang, Ping

2005-01-01

417

Picogram detection levels of asialofetuin via the carbohydrate moieties using the light addressable potentiometric sensor.  

PubMed

Fetal calf serum asialofetuin was assayed in the sandwich format using biotinylated and fluoresceinated ricin toxin (B-RCA and F-RCA). The sandwiched species was captured on a biotin-BSA coated nitrocellulose membrane with streptavidin. Anti-fluorescein antibody-urease conjugate was bound to the complex, and detected and quantitated under microvolume conditions using the light addressable potentiometric sensor. As little as 250 pg of asialofetuin was detectable whereas fetuin gave no response at conditions as high as 32 ng. Using a competitive inhibition assay, we established that the binding constant for the asialofetuin-ricin complex was 3.6 x 10(8) M-1. This is in good agreement with data published using glycopeptides derived from asialofetuin, and RCA and the ricin agglutinin, RCA-120. PMID:8595257

Dill, K; Olson, J D

1995-10-01

418

Cell-based biosensors based on light-addressable potentiometric sensors for single cell monitoring.  

PubMed

Cell-based biosensors incorporate cells as sensing elements that convert changes in immediate environment to signals for processing. This paper reports an investigation on light-addressable potentiometric sensor (LAPS) to be used as a possible cell-base biosensor that will enable us to monitor extracellular action potential of single living cell under stimulant. In order to modify chip surface and immobilize cells, we coat a layer of poly-L-ornithine and laminin on surface of LAPS chip on which rat cortical cells are grown well. When 10 microg/ml acetylcholine solution is administrated, the light pointer is focused on a single neuronal cell and the extracellular action potential of the targeted cell is recorded with cell-based biosensor based on LAPS. The results demonstrate that this kind of biosensor has potential to monitor electrophysiology of living cell non-invasive for a long term, and to evaluate drugs primarily. PMID:15681191

Xu, Gaixia; Ye, Xuesong; Qin, Lifeng; Xu, Ying; Li, Yan; Li, Rong; Wang, Ping

2005-03-15

419

Detection of nicotinic receptor ligands with a light addressable potentiometric sensor.  

PubMed

The nicotinic acetylcholine receptor, purified from Torpedo electric organ, was coupled to a light addressable potentiometric sensor (LAPS) to form a LAPS-receptor biosensor. Receptor-ligand complexes containing biotin and urease were captured on a biotinylated nitrocellulose membrane via a streptavidin bridge and detected with a silicon-based sensor. Competition between biotinylated alpha-bungarotoxin and nonbiotinylated ligands formed the basis of this assay. This biosensor detected both agonists (acetylcholine, carbamylcholine, succinylcholine, suberyldicholine, and nicotine) and competitive antagonists (d-tubocurarine, alpha-bungarotoxin, and alpha-Naja toxin) of the receptor with affinities comparable to those obtained using radioactive ligand binding assays. Consistent with agonist-induced desensitization of the receptor, the LAPS-receptor biosensor reported a time-dependent increase in affinity for the agonist carbamylcholine as expected, but not for the antagonists. PMID:1621972

Rogers, K R; Fernando, J C; Thompson, R G; Valdes, J J; Eldefrawi, M E

1992-04-01

420

GaN Thin Film Based Light Addressable Potentiometric Sensor for pH Sensing Application  

NASA Astrophysics Data System (ADS)

Gallium nitride (GaN) is a material with remarkable properties, including wide band gap, direct light emission and excellent chemical stability. In this study, a GaN-based light addressable potentiometric sensor (LAPS) with Si3N4 ˜50 nm as a sensing membrane is fabricated. By modulated optical excitation from an ultraviolet 365 nm light-emitting diode, the photoresponse characteristic and related pH sensitivity of the fabricated GaN-based LAPS is investigated. A Nernstian-like pH response with pH sensitivity of 52.29 mV/pH and linearity of 99.13% is obtained. These results of the GaN-based LAPS show great promise and it could be used as a single chemical sensor or integrated optoelectronic chemical sensor array for biomedical research with high spatial resolution.

Das, Atanu; Das, Anirban; Chang, Liann Be; Lai, Chao Sung; Lin, Ray Ming; Chu, Fu Chuan; Lin, Yen Heng; Chow, Lee; Jeng, Ming Jer

2013-03-01

421

[Potentiometric glucose determination in human serum samples with glucose oxidase biosensor based on iodide electrode].  

PubMed

Glucose potentiometric biosensor was prepared by immobilizing glucose oxidase on iodide-selective electrode. The hydrogen peroxide formed after the oxidation of glucose catalysed by glucose oxidase (GOD) was oxidized by sodium molybdate (SMo) at iodide electrode in the presence ofdichlorometane. The glucose concentration was calculated from the decrease of iodide concentration determined by iodide-selective sensor. The sensitivity of glucose biosensor towards iodide ions and glucose was in the concentration ranges of 1.0 x 10(-1) - 1.0 x 10(-6) M and 1.0 x 10(-2) - 1.0 x 10(-4) M, respectively. The characterization of proposed glucose biosensor and glucose assay in human serum were also investigated. PMID:23795482

Karakus, E; Pekyardimchi, Sh; Kilich, E

422

A new buffer system for the potentiometric determination of fluoride ion  

SciTech Connect

This paper attempts to eliminate the lengthy stage of hydrolytic separation of the elements during the potentiometric determination of fluoride ions and also to develop a universal method for the determination of flouride ions. During the development of a procedure for the determination of fluoride ions it is necessary to eliminate the interfering effects of elements which form stable fluoride complexes such as A1 (III), Fe (III), Si (III), Ti (IV), V (IV), Mo (V), and W (V). By the addition of diethylenetriaminepentaacetate to the buffer solution and preliminary extraction of the benzoylphenylhydroxylaminates of the interfering elements with chloroform it was possible to develop a method for the determination of fluoride with a detection limit of 1.10/sup -5/ M.

Zhobinskii, E.Y.; Askochenskaya, R.M.; Novikova, L.B; Wl' Figarov, O.S.

1985-05-01

423

Selectivity characteristics of potentiometric carbon dioxide sensors with various gas membrane materials  

SciTech Connect

The selectivity characteristics of potentiometric carbon dioxide sensors with regard to various organic and inorganic acid interferences have been systematically examined. When used in conjunction with a standard silicone rubber CO/sub 2/ permeable membrane, the sensor displays surprisingly large response to several organic acids having low volatility, e.g., benzoic, cinnamic, and salicylic acids. If the outer membrane is changed to a microporous Teflon material, the response to these substances is diminished, but poor selectivity over volatile organics and acidic gases results. The use of a new homogeneous Teflon-like membrane meterial is shown to offer dramatic improvement in selectivity for CO/sub 2/ over all of the compounds tested. The mechanistic reasons for this enhanced selectivity are discussed as are alternate methods for reducing organic acid interferences when using more conventional membrane materials. 4 figures, 1 table.

Kobos, R.K. (Virginia Commonwealth Univ., Richmond); Parks, S.J.; Meyerhoff, M.E.

1982-10-01

424

Real-Time Telemetry System for Amperometric and Potentiometric Electrochemical Sensors  

PubMed Central

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.

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

425

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

2011-09-02

426

Laser flash photolysis studies of dibenzosuberenyl cations and radical cations  

SciTech Connect

A variety of dibenzosuberenyl systems have been investigated by laser flash photolysis. Excitation of the parent alcohol, 5-dibenzosuberenol, in trifluoroethanol yields the corresponding carbocation via heterolysis of the C-OH bond. The carbocation shows a long-lived (> 100 {mu}s) absorption at 525 nm with a second band at 390 nm, is readily quenched by nucleophiles (k{sub q}(azide) = 1.1 {times} 10{sup 9} M{sup {minus}1} s{sup {minus}1}), and fluoresces with a lifetime of 35 ns. In other solvents, the transient phenomena are dominated by the formation of the radical cation via a two-photon process. both dibenzosuberene and 5-phenyl-5-dibenzosuberenol also yield radical cations in a variety of polar solvents. The radical cations show absorption spectra with maxima at 470 nm and a broad band in the 700-nm region, have lifetimes in oxygenated solutions of >1.5 {mu}s, and react with a variety of nucleophiles. Their identity has been confirmed on the basis of their independent generation with the electron-transfer sensitizers chloranil and 1,4-dicyanonaphthalene and by reaction with 1,2,4-trimethoxybenzene.

Johnston, L.J.; Lobaugh, J.; Wintgens, V. (National Research Council of Canada, Ottawa, Ontario (Canada))

1989-10-19

427

Introducing titratable water to all-atom molecular dynamics at constant pH.  

PubMed

Recent development of titratable coions has paved the way for realizing all-atom molecular dynamics at constant pH. To further improve physical realism, here we describe a technique in which proton titration of the solute is directly coupled to the interconversion between water and hydroxide or hydronium. We test the new method in replica-exchange continuous constant pH molecular dynamics simulations of three proteins, HP36, BBL, and HEWL. The calculated pKa values based on 10-ns sampling per replica have the average absolute and root-mean-square errors of 0.7 and 0.9 pH units, respectively. Introducing titratable water in molecular dynamics offers a means to model proton exchange between solute and solvent, thus opening a door to gaining new insights into the intricate details of biological phenomena involving proton translocation. PMID:23972860

Chen, Wei; Wallace, Jason A; Yue, Zhi; Shen, Jana K

2013-08-20

428

Acid-Base Titration of (S)-Aspartic Acid: A Circular Dichroism Spectrophotometry Experiment  

NASA Astrophysics Data System (ADS)

The magnitude of the circular dichroism of (S)-aspartic acid in aqueous solutions at a fixed wavelength varies with the addition of strong base. This laboratory experiment consists of the circular dichroism spectrophotometric acid-base titration of (S)-aspartic acid in dilute aqueous solutions, and the use of the resulting data to determine the ionization constant of the protonated amino group. The work familiarizes students with circular dichroism and illustrates the possibility of performing titrations using a less usual instrumental method of following the course of a reaction. It shows the use of a chiroptical property in the determination of the concentration in solution of an optically active molecule, and exemplifies the use of a spectrophotometric titration in the determination of an ionization constant.

Cavaleiro, Ana M. V.; Pedrosa de Jesus, Júlio D.

2000-09-01

429

Titration of free hydroxyl and strained siloxane sites on silicon dioxide with fluorescent probes.  

PubMed

A technique enabling the detection and quantification of low density sites on planar SiO2 surfaces is demonstrated. Fluorescent probes are used to titrate free hydroxyl and strained siloxane sites on the surface of amorphous SiO2 substrates in vacuum. The titration of free hydroxyl sites was performed to validate the method and to provide a reference for the measurement of the strained siloxane site density. Perylene derivatives with different functional groups are chemisorbed onto the surface sites, enabling in situ photoluminescence (PL) measurements of the bound fluorophores. An amine functional group is used to selectively titrate strained siloxane sites, while an alcohol group is used for the titration of free hydroxyl sites. Emission intensity was found to be nonlinear with coverage for bound fluorophore densities greater than 0.1 nm(-2), necessitating the removal of molecules from the surface into a solution to obtain accurate density measurements. For lower densities, the coverage of bound fluorophores can be estimated directly from in situ PL measurements. The measured areal densities of bound fluorophores after titrating free hydroxyl sites are in good agreement with literature values for the densities of such sites on high surface area silica. PL measurements of SiO2 surfaces titrated with an amine derivative of perylene indicate that strained siloxane sites exist for vacuum pretreatment temperatures of 300 °C and increase with increasing pretreatment temperature. Densities of strained siloxane sites on the silica surface are estimated at 0.004-0.02 nm(-2) for pretreatment temperatures of 300-700 °C, demonstrating the sensitivity of this technique. PMID:23978272

McCrate, Joseph M; Ekerdt, John G

2013-09-11

430

Effect of a Titration Polysomnogram on Treatment Success with a Mandibular Repositioning Appliance  

PubMed Central

Study Objectives: Mandibular repositioning appliance (MRA) therapy is a treatment option for patients with mild to moderate sleep apnea and for patients who do not tolerate continuous positive airway pressure. Titration of MRAs consists of sequential mandibular advancement guided by symptom improvement. The goal of the study was to determine if patients with an elevated apnea hypopnea index (AHI), despite the use of a subjectively optimized MRA, could achieve better results with additional titration during polysomnography (PSG). Methods: Patients were enrolled if they had an AHI ? 15/h and were referred for MRA therapy. The MRA was advanced until symptoms improved. During the PSG, the technologist monitored the patient's sleep and increased mandibular protrusion until the AHI was improved. Results: There was a significant improvement in AHI, minimum oxygen saturation, and total sleep time with the MRA before further advancement. At the final PSG, 65.2% of patients had an AHI ? 10 associated with at least a 50% reduction in AHI. The incomplete responders had their appliance further titrated, and this improved the results of MRA therapy by 30.4% to a total success rate of 95.6%. Conclusions: This study shows that it is possible to improve the results of MRA therapy by further advancing the appliance during a titration PSG in patients with an incomplete response. The titration night improved the results of the usual clinical advancement of the MRA with substantially more patients achieving a successful outcome. Citation: Almeida FR; Parker JA; Hodges JS; Lowe AA, Ferguson KA. Effect of a Titration Polysomnogram on Treatment Success with a Mandibular Repositioning Appliance. J Clin Sleep Med 2009;5(3):198-204.

Almeida, Fernanda R.; Parker, Jonathan A.; Hodges, James S.; Lowe, Alan A.; Ferguson, Kathleen A.

2009-01-01

431

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

432

Measurements of the capacitance and the response time of solid-state potentiometric sensors by an electrochemical time-of-flight method  

Microsoft Academic Search

A micro-electrochemical time-of-flight technique relying on galvanostatic ion generation and potentiometric sensing (P-ETOF) has been developed in order to characterize dynamic properties of solid-state potentiometric sensors and to measure their capacitance. Lithographically-fabricated generator-sensor devices featuring 10 ?m-wide micro-electrodes spaced by 20–50 ?m are used in either an open face mode, where hemi-cylindrical diffusion governs mass transport of generated ions, or in a

Katarzyna Slowinska; Marcin Majda

2004-01-01

433

Kinetic catalytic determination of trace levels of iodide based on the oxidation of basic dyes with hydrogen peroxide monitored potentiometrically using simple PVC electrodes  

Microsoft Academic Search

Four sensitive catalytic potentiometric methods have been developed for trace levels determination of iodide based on its catalytic effects on the oxidation of four dyes: viz. variamine blue (VB), rhodamine B (RB), methylene blue (MB) and malachite green (MG), with H2O2 in H3PO4 medium at 25±0.5°C. The catalyzed reaction rates were estimated potentiometrically by monitoring the potential of the corresponding

Elmorsy Khaled; M. A. El-Ries; F. I. Zidane; S. A. Ibrahim; M. S. Abd-Elmonem

2011-01-01

434

Monitoring of an RNA Multistep Folding Pathway by Isothermal Titration Calorimetry  

PubMed Central

Abstract Isothermal titration calorimetry was used to monitor the energetic landscape of a catalytic RNA, specifically that of the hepatitis delta virus ribozyme. Using mutants that isolated various tertiary interactions, the thermodynamic parameters of several ribozyme-substrate intermediates were determined. The results shed light on the impact of several tertiary interactions on the global structure of the ribozyme. In addition, the data indicate that the formation of the P1.1 pseudoknot is the limiting step of the molecular mechanism. Last, as illustrated here, isothermal titration calorimetry appears to be a method of choice for the elucidation of an RNA's folding pathway.

Reymond, Cedric; Bisaillon, Martin; Perreault, Jean-Pierre

2009-01-01

435

The influence of hydrogen peroxide and pH on the Mohr titration.  

PubMed

The official Japanese method for determination of chloride in hot-spring waters requires any H(2)S present to be oxidized with hydrogen peroxide in ammoniacal medium. When this was done, and the solution was titrated with silver nitrate at pH 9.7, the indicator colour changed from yellow to brownish grey, owing to reduction of silver ions to the metal by hydrogen peroxide. The effect can be eliminated by adjusting the pH to 7.0-7.5 before the titration. PMID:18965181

Fujita, R

1991-05-01

436

Divalent cations induce protofibril gelation.  

PubMed

Soluble fibrin oligomers (protofibrils) undergo phase change merely by adding 1-2 mM Ca2+ or 25-100 microM Zn2+. The cation-induced "protofibrin" clots appear similar to normally formed fibrin gels. Maximal clot turbidity of protofibrin gels increases with cations in a concentration-dependent manner. Magnesium (less than 0.5 mM) is ineffective in inducing protofibril gelation. Turbidity and degree of polymerization (DP) [indirectly expressed as AT (activation time)] appear to be positively correlated, regardless of whether the divalent cation is Ca2+ or Zn2+. Cross sections of Ca2+-induced protofibrin fibers are approximately 6-18-fibrin-monomers-thick. With both Ca2+ and 40 microM Zn2+, fiber cross section increases to 30-50 monomers thick. Negatively stained Zn2+-and Ca2+-induced protofibrin gels exhibit banding periodicity of approximately 240 A, similar to that of normally generated fibrin gels. Regions of lateral merging of individual segments of the protofibrin leads to increased cross section of the fiber and forms a branch required for gelation. These findings indicate that the rate of coagulation and the ultimate thickness of the fibers both relate to lateral associative processes of protofibrils, which are augmented by physiologic concentrations of 2+ and Zn2+. PMID:3341371

Marx, G

1988-02-01

437

How cations change peptide structure.  

PubMed

Specific interactions between cations and proteins have a strong impact on peptide and protein structure. Herein, we shed light on the nature of the underlying interactions, especially regarding effects on the polyamide backbone structure. This was done by comparing the conformational ensembles of model peptides in isolation and in the presence of either Li(+) or Na(+) by using state-of-the-art density-functional theory (including van der Waals effects) and gas-phase infrared spectroscopy. These monovalent cations have a drastic effect on the local backbone conformation of turn-forming peptides, by disruption of the hydrogen-bonding networks, thus resulting in severe distortion of the backbone conformations. In fact, Li(+) and Na(+) can even have different conformational effects on the same peptide. We also assess the predictive power of current approximate density functionals for peptide-cation systems and compare to results with those of established protein force fields as well as high-level quantum chemistry calculations (CCSD(T)). PMID:23853047

Baldauf, Carsten; Pagel, Kevin; Warnke, Stephan; von Helden, Gert; Koksch, Beate; Blum, Volker; Scheffler, Matthias

2013-07-12

438

Thermodynamic characterization of 3-[(3-cholamidopropyl)-dimethylammonium]-1-propanesulfonate (CHAPS) micellization using isothermal titration calorimetry: temperature, salt, and pH dependence.  

PubMed

A systematic investigation of the micellization process of a biocompatible zwitterionic surfactant 3-[(3-cholamidopropyl)-dimethylammonium]-1-propanesulfonate (CHAPS) has been carried out by isothermal titration calorimetry (ITC) at temperatures between 278.15 K and 328.15 K in water, aqueous NaCl (0.1, 0.5, and 1 M), and buffer solutions (pH = 3.0, 6.8, and 7.8). The effect of different cations and anions on the micellization of CHAPS surfactant has been also examined in LiCl, CsCl, NaBr, and NaI solutions at 308.15 K. It turned out that the critical micelle concentration, cmc, is only slightly shifted toward lower values in salt solutions, whereas in buffer media it remains similar to its value in water. From the results obtained, it could be assumed that CHAPS behaves as a weakly charged cationic surfactant in salt solutions and as a nonionic surfactant in water and buffer medium. Conventional surfactants alike, CHAPS micellization is endothermic at low and exothermic at high temperatures, but the estimated enthalpy of micellization, ?HM0, is considerably lower in comparison with that obtained for ionic surfactants in water and NaCl solutions. The standard Gibbs free energy, ?GM0, and entropy, ?SM0, of micellization were estimated by fitting the model equation based on the mass action model to the experimental data. The aggregation numbers of CHAPS surfactant around cmc, obtained by the fitting procedure also, are considerably low (nagg ? 5 ± 1). Furthermore, some predictions about the hydration of the micelle interior based on the correlation between heat capacity change, ?cp,M0, and changes in solvent-accessible surface upon micelle formation were made. CHAPS molecules are believed to stay in contact with water upon aggregation, which is somehow similar to the micellization process of short alkyl chain cationic surfactants. PMID:22686523

Krofli?, Ana; Sarac, Bojan; Bešter-Roga?, Marija

2012-07-02

439

Two analyte calibrations from the transient response of a single potentiometric sensor employed with the SIA technique.  

PubMed

Simultaneous quantification of Cd(2+) and Pb(2+) in solution has been correctly targeted using the kinetic information from a single non-specific potentiometric sensor. Dual quantification was accomplished from the complex information in the transient response of an electrode used in a Sequential Injection Analysis (SIA) system and recorded after step injection of sample. Data was firstly preprocessed with the Discrete Wavelet Transform (DWT) to extract significant features and then fed into an Artificial Neural Network (ANN) for building the calibration model. DWT stage was optimized regarding the wavelet function and decomposition level, while the ANN stage was optimized on its structure. To simultaneously corroborate the effectiveness of the approach, two different potentiometric sensors were used as study case, one using a glass selective to Cd(2+) and another a PVC membrane selective to Pb(2+). PMID:20006109

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

2010-01-15

440

Difference between the potentiometric surfaces of the Lower Patapsco aquifer in southern Maryland, September 1990 and September 2009  

USGS Publications Warehouse

This report presents a map showing the change in the potentiometric surface of the lower Patapsco aquifer in the Patapsco Formation of Early Cretaceous age in Southern Maryland between September 1990 and September 2009. The map, based on water level differences obtained from 45 wells, shows that the change of the potentiometric surface during the 19-year period ranged from increases of 25 feet at Indian Head and 4 feet near the outcrop area in Glen Burnie, to declines of 35 feet at Arnold, 56 feet at Severndale, 28 feet at Crofton Meadows, 73 feet at Waldorf, 79 feet near La Plata, 35 feet at the Morgantown power plant, and 32 feet at Swan Point. The map also shows well yield in gallons per day for 2008 at wells or well fields.

Curtin, Stephen E.; Andreasen, David C.; Staley, Andrew W.

2010-01-01

441

Nitrogenous synergists induced potentiometric response to metal ions with polymeric liquid membranes containing thenoyltrifluoroacetone as an ionophore.  

PubMed

The effects of nitrogenous synergists on the potentiometric responses to divalent transition metal ions were investigated concerning polymeric liquid membranes containing thenoyltrifluoroacetone (Htta) as an ionophore. The tested synergists were pyridine (py) and 4,4'-dioctyl-2,2'-bipyridyl (C8bpy). The potentiometric responses to metal ions, such as Cd2+, Co2+, Ni2+ and Zn2+, were induced by adding the synergists into the liquid membrane systems. The coexistence of Htta and a synergist was necessary for generating the membrane potential. The tta- anion adsorbed at the liquid membrane/solution interface and the complex formation between the synergist and a given metal ion appeared to participate in preferential uptake of metal ions. PMID:16512411

Itoh, Yasoo; Ueda, Yoshihisa; Sugawara, Masao; Kataoka, Masamitsu; Sato, Hitoshi; Umezawa, Yoshio

2006-02-01

442

Lipoplex Thermodynamics: Determination of DNA-Cationic Lipoid Interaction Energies  

PubMed Central

An experimental study of the cationic lipid-DNA binding affinity is presented. The binding free energy was determined by monitoring lipoplex dissociation under conditions of increasing salt concentration. The primary procedure was based on the extent of quenching by energy transfer of fluorophores on DNA molecules by fluorophore on a lipid as these molecules came into close association in the lipoplex. Titration calorimetry on the Dickerson dodecamer was also done, with results that were in agreement with the fluorescence data. Measurements on short oligonucleotides allowed estimation of the binding energy per nucleotide. The binding free energy is ?0.6 kcal/mole nucleotide for the Dickerson dodecamer and declines for longer oligonucleotides. The entropy gained upon complex formation is ?1 entropy unit per released counterion. The method was applied to long DNA molecules (herring and ?-phage DNA) and revealed that complete dissociation occurs at 750 mM NaCl. Likely contributions of macromolecular desolvation and DNA flexibility to the binding energy are discussed.

Pozharski, Edwin; MacDonald, Robert C.

2003-01-01

443

Dioxouranium(VI)-carboxylate complexes. A calorimetric and potentiometric investigation of interaction with oxalate at infinite dilution and in NaCl aqueous solution at I=1.0 mol L(-1) and T=25 degrees C.  

PubMed

In this paper we investigated the interactions between dioxouranium(VI) and oxalate using (H(+)-glass electrode) potentiometry and titration calorimetry. Potentiometric measurements were carried out in NaCl aqueous solutions and at T=25 degrees C in a wide range of experimental conditions (concentrations, ligand/metal molar ratio, pH, titrants) at low ionic strength values (I< or =0.090mol L(-1), without supporting electrolyte) and at I=1.0mol L(-1); different procedures were employed for the acquisition of experimental data and careful analysis of these data performed. In all cases the speciation model that best fits experimental data takes into account the formation of the binary mononuclear species UO(2)(ox)(0), UO(2)(ox)(2)(2-), UO(2)(ox)(3)(4-) widely reported in literature, the ternary hydroxyl mononuclear species UO(2)(ox)OH(-), UO(2)(ox)(OH)(2)(2-), UO(2)(ox)(2)OH(3-), UO(2)(ox)(3)OH(5-), the protonated ternary mononuclear species UO(2)(ox)(3)H(3-) and the binuclear species (UO(2))(2)(ox)(5)(6-). Calorimetric measurements were carried out following similar procedures and in the same experimental conditions as employed for the potentiometric measurements at I=1.0mol L(-1) in NaCl. The stability of UO(2)(2+)-oxalate(2-) complexes is fairly high and their main contribution to stability is entropic in nature. Some linear empirical relationships were found which make it possible to calculate (i) the contribution of a single bond: DeltaG(sb) degrees =-16.6+/-0.2kJ mol(-1) and TDeltaS(sb) degrees =16.2+/-0.5kJ mol(-1); (ii) chelate stabilisation per ring: DeltaG(r) degrees =-1.30+/-0.04kJ mol(-1) and TDeltaS(r) degrees =1.27+/-0.23kJ mol(-1) and (iii) the mean stability of negatively charged Na(+)-ion pair complexes: log(T)K=(0.46+/-0.02).|z| (z=charge of complex species), DeltaG degrees =-(2.60+/-0.1).|z|kJ mol(-1) and TDeltaS degrees =2.5+/-0.5kJ mol(-1). Both potentiometric and calorimetric results provide evidence of the penta-coordination of the species UO(2)(ox)(3)(4-). SIT parameters were calculated from the data at I=0 and I=1.02mol kg(-1). Comparisons are made with literature data. An insoluble dioxouranium(VI) ternary complex was synthesised (at I=1.0mol L(-1) in NaCl) and characterised by thermoanalysis and elemental analysis. PMID:19071399

Crea, Francesco; De Robertis, Alessandro; De Stefano, Concetta; Sammartano, Silvio

2006-07-07

444

High-temperature potentiometric\\/amperometric NO x sensors combining stabilized zirconia with mixed-metal oxide electrode  

Microsoft Academic Search

Electrochemical sensors using stabilized zirconia and oxide electrodes were tested for detecting NO or NO2 potentiometrically and amperometrically at high temperature. For a mixed-potential-type NOx sensor of two-electrode structure, CdCr2O4 was found to give fairly excellent NOx sensing characteristics among the perovskite-type and spinel-type oxides tested. The CdCr2O4-attached device gave a linear correlation between EMF and the logarithm of NO

Norio Miura; Geyu Lu; Noboru Yamazoe

1998-01-01

445

Potentiometric Study of the Effect of Sodium Dodecylsulfate and Dioxane on the Hydrolysis of the Aluminum(III) Ion  

Microsoft Academic Search

Hydrolytic equilibria of the aluminum(III) ion were studied in the presence of a surfactant, sodium n-dodecylsulfate (SDS) and, separately, in mixed water + dioxane and water + dioxane + surfactant media at 298.15 K, by using\\u000a potentiometric measurements with a glass electrode. The concentration of SDS was between 1.25 and 25.0 mmol-dm?3, whereas the volume percent of dioxane was varied

Ratomir M. Jeli?; Ljubinka G. Joksovi?; Predrag T. Djurdjevi?

2005-01-01

446

Label-free biosensor: A novel phage-modified Light Addressable Potentiometric Sensor system for cancer cell monitoring  

Microsoft Academic Search

Early diagnosis has become the most important factor influencing the cancer's curing efficiency in clinical medicine. Here we present a new way for detection of cancer markers and cancer cells based on phage-modified Light Addressable Potentiometric Sensor (phage-LAPS). Phages were immobilized on the Si3N4 chip surfaces covalently. Using the back-illuminating system, this phage-LAPS is tested to detect human phosphatase of

Yunfang Jia; Ming Qin; Hongkai Zhang; Wencheng Niu; Xiao Li; Likai Wang; Xin Li; Yunpeng Bai; Youjia Cao; Xizeng Feng

2007-01-01

447

Novel combination of digital light processing (DLP) and light-addressable potentiometric sensors (LAPS) for flexible chemical imaging  

Microsoft Academic Search

Chemical imaging systems allow the visualisation of the distribution of chemical species on the sensor surface. This work represents a new flexible approach of read out in a light-addressable potentiometric sensor (LAPS) with the help of a digital light processing (DLP) set-up. The DLP, known well for video projectors, consists of a mirror-array MEMS device which allows fast and flexible

Torsten Wagner; Ko-ichiro Miyamoto; Michael J. Schöning; Tatsuo Yoshinobu

2010-01-01

448

A Light-Addressable Potentiometric Sensor System for Fast, Simultaneous and Spatial Detection of the Metabolic Activity of Biological Cells  

Microsoft Academic Search

The metabolic activity of cells can be utilised to indicate the general reaction of them towards the cell environment. Hence, the influence of a specific reagent (e.g., drugs, toxins, growth factors, etc.) in the cell-culture medium can be determined by recording the metabolic activity. The light-addressable potentiometric sensor (LAPS), a field-effect-based chemical sensor, provides a promising technology platform to record

T. Wagner; R. Molina; M. Biselli; M. Canzoneri; T. Schnitzler; T. Yoshinobu; M. J. Schoning

2007-01-01

449

Use of a Light-Addressable Potentiometric Sensor for the Detection of Escherichia coliO157:H7  

Microsoft Academic Search

We describe the development of an immunoligand assay (ILA) in conjunction with a light-addressable potentiometric sensor (LAPS) for the rapid detection ofEscherichia coliO157:H7 cells in buffered saline. The ILA protocol consists of “sandwiching” bacterial analyte between biotinylated and fluoresceinated antibodies, indirect enzyme labeling of the bacteria with urease-labeled anti-fluorescein antibody, and active capture of the immune complex at a biotinylated

Andrew G. Gehring; Deidre L. Patterson; Shu-I Tu

1998-01-01

450

A non-labeled DNA biosensor based on light addressable potentiometric sensor modified with TiO 2 thin film  

Microsoft Academic Search

Titanium dioxide (TiO2) thin film was deposited on the surface of the light addressable potentiometric sensor (LAPS) to modify the sensor surface\\u000a for the non-labeled detection of DNA molecules. To evaluate the effect of ultraviolet (UV) treatment on the silanization level\\u000a of TiO2 thin film by 3-aminopropyltriethoxysilane (APTS), fluorescein isothiocyanate (FITC) was used to label the amine group on\\u000a the

Xiao-lin Zong; Chun-sheng Wu; Xiao-ling Wu; Yun-feng Lu; Ping Wang

2009-01-01

451

Flexible electrochemical imaging with “zoom-in” functionality by using a new type of light-addressable potentiometric sensor  

Microsoft Academic Search

The light-addressable potentiometric sensor (LAPS) is capable to visualize chemical concentrations above the sensor structure, hence, generating chemical images. To read-out the sensors, a light pointer illuminates the sensor pixel-by-pixel and the resulting photocurrent will be determine. The lateral dimensions of a single pixel and the image resolution can be controlled by shaping the light pointer accordingly. This work demonstrates

T. Wagner; K. Miyamoto; C. F. Werner; M. J. Schoning; T. Yoshinobu

2011-01-01

452

Immobilization of Urease and Cholinesterase on the Surface of Semiconductor Transducer for the Development of Light-Addressable Potentiometric Sensors  

Microsoft Academic Search

Various methods for the immobilization of urease and butyrylcholinesterase on the insulator surface of a laser-scanned semiconductor transducer (LSST) have been tested and compared for the development of an enzyme-based light-addressable potentiometric sensor (LAPS). The method of preparing photocurable membranes on LAPS is presented, and a new type of enzyme LAPS with photocurable polymeric enzyme membranes has been elaborated. It

Ioulia G. Mourzina; Tatsuo Yoshinobu; Yuri E. Ermolenko; Yuri G. Vlasov; Michael J. Schöning; Hiroshi Iwasaki

2004-01-01

453

Comparison of potentiometric enzyme sensors for urea and penicillin-G: differential thick-film sensors versus classical electrodes  

Microsoft Academic Search

A comparative study of urease and penicillinase biosensors was performed in which different transducers were compared, i.e. pH glass electrodes, macroscopic ion-selective electrodes and thick-film transducers. For enzyme immobilization onto the transducers aqueous dispersion polymers were used in all cases in this work. Since these sensors are based on potentiometric measurements the lack of a classical reference electrode when solid

Christian Eppelsheim; Ralph Aubeck; Norbert Hampp

1995-01-01

454

Development of a potentiometric procedure for determination of glycerol and 2,3-butanediol in wine by sequential injection analysis  

Microsoft Academic Search

A sequential injection procedure with potentiometric detection for determination of glycerol and 2,3-butanediol in wine is described. The method was based on reaction of IO?4 ions with glycerol and 2,3-butanediol with the reagent consumption afterwards being continuously monitored by means of a PVC periodate ion selective electrode constructed with tubular configuration and without inner reference solution. The electrode membrane was

Gilmara C Luca; Boaventura F Reis; Elias A. G Zagatto; Maria Conceição B. S. M Montenegro; Alberto N Araújo; José Luis F. C Lima

1998-01-01

455

Modification of a pH-Titration Standardization Method for Formaldehyde  

Microsoft Academic Search

Procedures for monitoring formaldehyde concentration in air ultimately require a standard solution with which to calibrate the response of the analytical method. Although formaldehyde solutions of nominal concentration may be prepared from a variety of sources, the solutions must be standardized. The sulfite-pH\\/ titration method was tested and found to give erratic results. This paper presents evidence to indicate that

Reimar R. W. Gaertner

1988-01-01

456

Comprehensive Formulation of Titration Curves for Complex AcidBase Systems and Its Analytical Implications  

Microsoft Academic Search

This article provides extensive and exhaustive mathematical description of titration curves related to acid-base systems with mixtures of mono- and polyprotic acids and their salts and bases involved. The related curves are presented in compact forms facilitating further operations made for particular needs. Some derivative properties of the curves, such as buffer capacity and inflection points, are also discussed. The

Agustin G. Asuero; Tadeusz Micha?owski

2011-01-01

457

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

458

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

459

Determination of the molecular weight distribution of polyacrylonitrile by turbidimetric titration  

Microsoft Academic Search

candescent lamp served as the light source. A cuvette containing the solution to be titrated was placed in the path of one of the light beams. The optical density of the solution was measured with a Pulfrich refractometer (k = 5330 A). The cuvette (capacity 100 ml) was tetrahedral in shape and was made of plane-parallel glasses and Teflon sheets,

L. S. Gembitskii; G. G. Uglanova

1970-01-01

460

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…

Dungey, Keenan E.; Epstein, Paul

2007-01-01

461

Comparison Optimal Pressure between Automatic Titrating and Predicting Continuous Positive Airway Pressure  

Microsoft Academic Search

Background: Optimal continuous positive airway pressure (CPAP) level reduced excessive daytime sleepiness and improved healthy status compared with subtherapeu- tic CPAP pressure for patients with obstructive sleep apnea syndromes. To date there have been no studies comparing the differences between the auto- matic CPAP titrating pressure levels (ACPAPL) and the predicting CPAP pressure levels (PCPAPL). In this study, we compared

Chung-Chieh Yu; Chung-Ching Hua; Jo-Chi Tseng; Yu-Chi Liu

2006-01-01

462

Differential spatial memory impairment after right temporal lobectomy demonstrated using temporal titration  

Microsoft Academic Search

Summary In this study a temporal titration method to explore the extent to which spatial memory is differentially impaired following right temporal lobectomy was employed. The spatial and non-spatial memory of 19 left and 19 right temporal lobectomy (TL) patients was compared with that of 16 normal controls. The subjects studied an array of 16 toy objects and were subsequently

J. A. Nunn; F. J. X. Graydon; C. E. Polkey; R. G. Morris

1999-01-01

463

Oxygen use for preterm infants: factors that may influence clinical decisions surrounding oxygen titration.  

PubMed

Preterm infants in neonatal intensive care units frequently require oxygen therapy. Clinicians are responsible for titrating oxygen to maximize the benefits and minimize the risks of this therapy. Studies have identified various toxic effects of oxygen on the developing tissues of the preterm infant; however, optimal target SpO(2) ranges have not been identified. Current trends in neonatology are focusing on defining optimal oxygen saturation ranges to improve infant outcomes and to decrease complications associated with the oxygen use. Consequently, research-based guidelines are being developed in neonatal intensive care units to guide oxygen administration. As target oxygen saturation ranges are developed, issues regarding health care professional compliance with these ranges have been identified. The specific reasons for this noncompliance have not been widely explored. However, factors such as nursing shortages, staffing issues, and a de-emphasis on staff education surrounding oxygen use have been offered as possible reasons. Understanding factors shaping clinical decision-making about oxygen titration is critical when designing policies and educational programs to change oxygen titration practice and ultimately improve patient outcomes. In this article, the literature outlining the importance of oxygen titration for preterm infants is reviewed. Discussion then focuses on factors that influence clinical decision-making and how these factors may influence decisions surrounding the use of oxygen for preterm infants. PMID:21285649

Johnson, Krystal; Scott, Shannon D; Fraser, Kimberly D

2011-02-01

464

Monitoring and Predicting Emulsion Stability of Metalworking Fluids by Salt Titration and Laser Light Scattering Method  

Microsoft Academic Search

The prediction of emulsion stability is very important in the study, formulation, quality control, and technical service of metalworking fluids. Conventional emulsion stability test methods can be very time consuming. One quick method to determine emulsion stability is to titrate an emulsion with a salt solution until the emulsion separates. The salt (or electrolyte) concentration at which an emulsion starts

YIXING PHILIP ZHAO; RUSS TURAY; LLOYD HUNDLEY

2006-01-01

465

Thermodynamics of Interaction between Some Cellulose Ethers and SDS by Titration Microcalorimetry  

Microsoft Academic Search

A titration calorimetric study of the interaction between nonionic cellulose ethers and ionic surfactant (SDS) has been extended to a larger number of polymers to explore the effect of variation of polymer hydrophobicity on the energetics of the process. “Hydrophobicity” as used here is an overall effect of the nature, degree, and number of substituents and is characterized by the

Satish Kumar Singh; Stefan Nilsson

1999-01-01

466

Thermodynamics of Interaction between Some Cellulose Ethers and SDS by Titration Microcalorimetry  

Microsoft Academic Search

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°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

Satish Kumar Singh; Stefan Nilsson

1999-01-01

467

Refinement and feasibility testing of a manual micro-method for protamine titration.  

PubMed

Current clinical recommendations for unfractionated heparin (UFH) therapy suggest target APTT ranges should reflect heparin concentrations of 0.2-0.4 IU/ml by protamine titration or 0.35-0.7 IU/m by an anti-Xa assay. Historically, performance of a manual protamine titration assay has been labour intensive and required a large plasma sample. However, recent studies have described difficulties with standardizing anti-Xa assays and demonstrated poor correlation of anti-Xa assays in children. This study aimed to refine and test the feasibility of a modified protamine titration assay using 100 microl of plasma. The resultant method produced reliable and repeatable results in adult plasma pools spiked with UFH. The feasibility of this method was proven by testing of in vivo heparinised samples obtained from children. This protamine titration method may offer an alternative to anti-Xa assays for clinical monitoring of children on heparin therapy, and will enhance clinical studies investigating paediatric-specific management of UFH therapy. PMID:18371057

Newall, F; Johnston, L; Ignjatovic, V; Summerhayes, R; Monagle, P

2008-03-21

468

A Comparison of Argentometric Titration and Spectrophotometric Determination of Chloride Concentration in Precipitation Samples  

Microsoft Academic Search

The concentration of chloride was detertnmed in parallel for a series of 14 precipltatron samples, by argentometric titration (Mohr method) at the laboratory ofthe Environmental Protection Agency Suceava and by spectrophotometrrc mercury thiocyanate-rron method at the Forest Research Station Cnmpulung Moldovenesc The purpose was to permrt the comparison of the chloride deposition obtained m time by ddrfferent laboratorres that had

CARMEN JACOBAN

469

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