Calcium ion selective membrane electrode

The calcium salts of the mono- and diesters of [4-(1,1,3,3-tetramethylbutyl)phenyl phosphoric acid] have been prepared, and the individual esters as well as mixtures of the esters have been used with several varieties of polyvinyl chloride to construct macro membrane electrodes selective to calcium ions. These electrodes have been calibrated by using solutions of CaCl₂ and Ca ion buffers. The mixed ester electrodes showed Nernstian response in the concentration range 10^-1 to 10^-7M; the diester electrodes showed Nernstian response down to 7.9 x 10^-8M. The detection limit of the mixed ester electrode was 10^-8M, whereas that of the diester electrode was 7.9 x 10^-9M. Contrary to these results, the monoester electrodes showed unsatisfactory behavior. The responses of both the mixed ester and diester electrodes to calcium ions were not affected by the presence of sodium, potassium, or other divalent ions. Only ferric and lanthanum ions showed interferences with the electrode response to calcium ions. p]The electrode response was independent of pH in the approximate range 5–8 at a CaCl₂ concentration of 10^-4M. As the Ca ion concentration was increased, the range of pH independence widened to approximately 4–8. The dynamic response time constant of the mixed ester electrode was in the range 0.7–1.5 sec, whereas that of the diester electrode was in the range 0.5–0.75 sec.     

Voltammetric,potentiometric and amperometric studies with a rotated aluminum wire electrode : Amperometric titration of fluoride with aluminum

The rotated aluminum electrode is a suitable indicator electrode in the amperometric titration of fluoride, Fluoride in concentrations varying between 1.10^-4 and 2.10^-3M was titrated with a standard aluminum nitrate solution in aqueous buffer solutions (pH between 3.6 and 46) Equilibrium was established within 15 mim. The fluoride-aluminum ratio at the (true) end-point was found to increase from 2 2 in 10^-4M fluoride to 28 in. 2.10^-3M fluoride. The titration calculated from the stability constants of the various aluminum-fluoride complexes were found to be in excellent agreement with the experimental curves.From a practical point of view titration in an acetate buffer in 50% alcohol in the presence of 0 5 M potassium or sodium nitrate is recommended. The fluoride-aluminum ratio at the end-point was found to be 5 9 ± 0 1 and independent of the fluoride concentration.     

Voltammetric,potentiometric and amperometric studies with a rotated aluminum wire electrode : A comparison of the baker and morrison cell with the raie.

In the amperometric determination of fluoride at the RAIE a half cell composed of 5% cadmium amalgam in equilibrum with a solution 1 M in cadmium sulfate and saturated with potassium chloride can be used as a reference electrode in a short-circuited cell instead of applying a potential of -0 75 V versus the saturated calomel electrode The standard addition method can be used in the presence of air, although removal of oxygen is recommended Using the Baker and Morrison electrode versus the above half cell and following their directions (10 ml solution, magnetic stirring) proportionality between current and fluoride concentration in a range between 1 · 10^-5 and 1 · 10^-4M was found in oxygen-free solutions Halides and perchlorates do not interfere. The standard addition technique can be used in the determination of fluoride in an unknown.     

Extraction-photometric determination of vanadium(V) with N-hydroxy-N-m-tolyl-N′-(2-methyl-5-chloro)phenyl-p-toluamidine hydrochloride in the presence of acetic,monochloroacetic, and phenylacetic acids

N-Hydroxy-N-m-tolyl-N′-(2-methyl-5-chloro)phenyl-p-toluamidine hydrochloride (HTMCPTH), a monobasic and bidentate chelating agent which reacts with vanadium(V) in carboxylic acid media to develop a blue-violet complex, has been employed as a highly selective reagent for extraction and direct photometric determination of the metal. Solvent extraction experiments indicate that from aqueous acetic acid (1.0–10.0 M), monochloroacetic acid (0.1–10.0 M), and phenylacetic acid (at pH 0.5–6.0) vanadium(V) is quantitatively extracted into chloroform. Almost all common ions including Fe³⁺, Cu²⁺, Ni²⁺, Co²⁺, Mn²⁺, Cr³⁺, Ti⁴⁺, Zr⁴⁺, and Mo⁶⁺ do not interfere with the proposed method. The procedure has been utilized for accurate determination of vanadium in standard steels.     

Alternating current polarographic determination of microgram amounts of iodide ion by means of the catalytic oxidation of 1-amino-2-naphthol-4-sulfonic acid

The catalytic oxidation of 1-amino-2-naphthol-4-sulfonic, acid proceeds quickly with microgram amounts of iodide in the presence of sodium chlorate at pH between 1.3 and 2.0. The oxidation product shows a sensitive tensammetric wave at potentials of about +0.03 V vs. SCE (pH 1.75), so that the catalytic reaction was applied for the determination of microgram amounts of iodide ion. The most suitable conditions of the pH range, the concentration of ANS and sodium chlorate, reaction temperature and standing are 1.3–2.0, 3 × 10^?4M, 0.05 M, 50° C and 1 h respectively. Using the recommended procedure, iodide ion can be determined precisely in the concentration range 0.4–6.5 ng ml^?1 with a relative error of about 3%. Interference of foreign species and the application to the determination of total iodine in river and sea water are described.     

The electrochemical stripping determination of tin in aqueous and nonaqueous media after its extraction

The anodic stripping voltammetric and chronopotentiometric determination of tin(IV) in aqueous and nonaqueous medium after its extraction using the rotating disc electrode made of glassy carbon with the mercury film was studied. The optimum composition of nonaqueous medium for the determination of tin is 0.2 M NaBr+5×10^?5M Hg²⁺ in 20 ml of the extract +30 ml of methanol. Tin(IV) was determined by anodic stripping voltammetry or chronopotentiometry down to the concentration 10^?7M. The selective determination of tin was studied. 10^?6M of tin(IV) was determined with an error ±4–5% even in the presence of metals: Co²⁺, Ni²⁺, Cd²⁺, Zn²⁺ (5×10^?3M), Ag⁺ and Pb²⁺ (5×10^?4M), Cu²⁺ (1.5×10^?4M), Sb³⁺ and Bi³⁺ (5×10^?5M).     

Determination of niacin and niacinamide in pharmaceutical products by automatic discrete-sample analysis

A spectrophotometric method is proposed for the determination of small amounts of iodide. The method is based on the reduction of bis(neocuproine)-coppcr(II) to the monovalent copper chelate cation in the aqueous phase by iodide ion and subsequent solvent extraction into chlorobenzene of the ion-pair formed between bis(neocuproine)copper(I) cation and the tri-iodide anion. At least a 5-fold molar amount of the copper(II) chelate cation, relative to iodide, is needed, and the optimal pH range is 3–5. The absorbance of the extract at 370 nm is a linear function of iodide concentration in the aqueous phase over the range 5·lO^-6–4·10^-5M (ca. 0.6–5 p.p.m.). The relative standard deviation was 1.0%. Large amounts of fluoride and chloride (2000-fold molar) and bromide (50-fold) did not appreciably affect the determination of iodide. The extraction mechanism is elucidated.     

The electrochemical stripping determination of bismuth in aqueous and nonaqueous media after its extraction

The cyclic voltammetry of bismuth in aqueous media and electrochemical stripping determination of bismuth in aqueous and nonaqueous media after its extraction using a rotating disc electrode of glassy carbon was studied. To raise the conductivity of the organic medium and for the preparation of a convenients medium for the determination of bismuth, an alcoholic (methanol) solution of NH₄SCN+HClO₄ was employed. In non-aqueous medium bismuth can be determined down to concentrations 10^?8M by anodic stripping voltammetry and to 5×10^?8M by anodic stripping chronopotentiometry. The selectivity of the determination of bismuth after its extraction was studied. Electrochemical determination of 10^?6M Bi³⁺ with error ±3–4% was not interfered with by these elements: Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, As³⁺ in the concentration 8×10^?3M, Fe³⁺, In³⁺, Sn²⁺ and Sn⁴⁺ (5× 10^?3M), Cu²⁺ (10^?3M), Sb³⁺ (1.5×10^?4M) and Hg²⁺ (2×10^?5M). The reproducibility of the electrochemical determination of bismuth according to the recommended procedure is very good.     

Voltammetric,potentiometric and amperometric studies with a rotated aluminum wire electrode: The R.Al.E. as indicator electrode in potentiometric and amperometric acid-base titrations

The effect of varying concentrations of fluoride on the potential of the R.AI.E. in acid buffer solutions is reported. In the pH range between 1 and 5.5 the potential becomes 30 mV more negative per unit increase in pH at fluoride concentrations between 10^-3 and 10^-4M. At a given pH the potential becomes 100 mV more negative when the fluoride concentration is increased from 10^-4 to 10^-3it. No depolarization occurs and no reproducible potentials can be measured in phosphate buffers of pH 6 to 8, even in the presence of 10^-3M fluoride. This concentration of fluoride causes depolarization and establishment of reproducible potentials in veronal buffers of reproducible pH 6 to 8. At a pH greater than 9 fluoride has no effect on the electrode potential which now becomes determined by pH. In the presence of fluoride, oxygen shifts the electrode potential to less negative values (mixed potential). Examples of potentiometric and amperometric titrations of strong and weak acids are given with the R.AI.E. as indicator electrode.     

Oxidation of organic substances with compounds of trivalent manganese: XXIII. Preparation,stability, and determination of the titer of standard solutions of the fluoride complex of trivalent manganese

A method of preparation of 10^?2 ?10^?3M standard solutions of the fluoride complex of manganese(III) by the reaction of manganese(II) with permanganate in a medium of potassium fluoride acidified with sulfuric acid has been developed. It has been found that in a medium of 1 M sulfuric acid, 0.5 M manganese(II) sulfate, and 0.1 M potassium fluoride these solutions are sufficiently stable for both direct and indirect titrimetric determinations. The titer was determined using potassium iodide as a primary standard and potentiometric, bipotentiometric, or biamperometric titration.     

A calcium-sensitive microelectrode suitable for intracellular measurement of calcium(II) activity

A calcium-selective microelectrode with a l-μm diameter tip suitable for impaling single neurons has been developed. The electroactive material is di[p-(1,1,3,3-tetramethyl-butyl) phenyl] phosphoric acid (t-HDOPP). The selectivity coefficients are about 5 · 10^-7 for k_Ca,K, 1–4·10^-7 for k_Ca,Na, and 10^-3 for k_Ca,Mg. Values reported previously for other calcium-selective electrodes based on long-chain phenylphosphoric acids are given for comparison. The calcium-selective microelectrodes have a linear response in 0.2 M KCl solutions over the range 10^-2–10^-XXX M CaCl₂; 10^-7 and 10^-8 M CaCl₂ solutions containing 0.2 M KCl can be detected but the response is not linear.     

Extraction studies of antimony bromide into benzene

Antimony(III) can be extracted rapidly and quantitatively into benzene from a 10 M H₂SO₄–0.03 M HBr system. The extracted antimony bromide has an antimony to bromine ratio of 1:3. Under the above optimum conditions for extraction of antimony, the behaviour of 35 other elements was studied; As³⁺, Ge⁴⁺, Se⁴⁺, and Sn²⁺ were extracted almost quantitatively, and the percentage extraction of Hg²⁺, Bi³⁺, and Te⁴⁺ was 74.1%, 10% and 5.5% respectively. The extraction of the elements into benzene from a 5 M H₂SO₄–0.01 M KI system was also investigated, A comparison of the two systems is given.     

Direct potentiometric titration of thiosulfate,thiourea, and ascorbic acid with lodate using an iodide ion-selective electrode

A potentiometric method has been developed for the semi-automatic direct titration of thiourea, thiosulfate, and ascorbic acid with potassium iodate in strongly acidic solutions using an iodide ion-selective electrode to monitor the reaction and locate the endpoint. The method is simple, fast, precise, and accurate. Amounts ranging from 0.15–1.5 mg of thiourea (3.9 × 10^?4–3.9 × 10^?3, M), 0.3–3.0 mg of thiosulfate (5.4 × 10^?4–5.4 × 10^?3, M), and 0.5–5.0 mg of ascorbic acid (5.7 × 10^?4–5.7 × 10^?3, M) have been determined with an average error of about 1%. The method has been applied to the determination of ascorbic acid in tablets. Results checked closely with those obtained with a standard titrimetric method.     

Bestimmung kleiner Nitrit- und Nitratkonzentrationen in wässrigen Ammoniaklösungen

The optimum conditions have been established for the spectrophotometric determination of nitrite with procaine and α-naphthylamine, for the range 10^?6–10^?2M, and of nitrate with chromotropic acid in the range 10^?5–10^?2M, both in aqueous solutions of ammonia at concentrations up to 16M. Both methods have been investigated and the results checked by statistical analysis. The procedures for the determinations are described.     

ISolement du groupe des terres rares de l'apatite par l'acide di-(2-ethyhexyl)phosphorique (hdehp)

The liquid-liquid extraction of rare-earth elements (REE) by 0.75 M di-(2-ethylhexyl) phosphoric acid (HDEHP) in cyclohexane from perchloric acid (1–12M) has been investigated. At moderate perchloric acid molarities (1–6 M), the distribution coefficient, E, has an inverse third-power dependency upon the acid concentration in the aqueous phase. However, at higher perchloric acid concentrations, the slope of the resulting curve is about +18, which means a change in the extraction mechanism. In 12 M perchloric acid medium, REE are quantitatively and selectively extracted from apatite minerals, in the organic phase. In order to strip out all the lanthanides, back-extractions were carried out with 9 M hydrochloric acid solutions.     

Solubility of YF<Subscript>3</Subscript>, CeF<Subscript>3</Subscript>, PrF<Subscript>3</Subscript>, NdF<Subscript>3</Subscript>, and DyF<Subscript>3</Subscript> in solutions containing sulfuric and phosphoric acids

The solubility of YF₃, CeF₃, PrF₃, NdF₃, and DyF₃ in solutions containing 0–4.496% mol/L (0–35 wt %) of H₂SO₄ and 0–27.6 g/L of H₃PO₄ (0–20 g/L of P₂O₅) at 20 °C was determined. Higher solubility in sulfuric acid solutions compared to that in hydrochloric and phosphoric acid solutions was attributed to the formation of fluorosulfate complexes M₂(SO₄)F₄(M = Y, Ce, Pr, Nd, Dy). The effect of minor concentrations of the phosphate ions on the solubility of YF₃, CeF₃, PrF₃, NdF₃, and DyF₃ in sulfuric acid solutions and the effect of fluoride ions on the recovery of lanthanides during sulfuric acid leaching from the phosphohemihydrate were discussed.     

Determination of tetracycline and related compounds using plastic membrane ion-selective electrodes

PVC membrane electrodes selective for hydrochlorides of tetracycline (TC), doxycycline (DC) and oxytetracycline (OTC) are prepared. The electrodes show a linear response with Nernstian slope over the range of 1.6 × 10⁻⁵–10⁻²M, 7.9 × 10⁻⁵–1.9 × 10⁻³M, and 6.3 × 10⁻⁵–6.3 × 10⁻³M for TC, DC, and OTC, respectively. The effects of pH of the test solution and time of soaking on the electrodes' performance are studied. The electrodes exhibit good selectivity for the investigated antibiotics with respect to a large number of inorganic cations and organic substances of biological importance. TC, DC, and OTC are determined successfully in pure solutions and in some pharmaceutical preparations using the standard additions method.     

Cyclodextrin-Modified Gold Nanoparticle Capillary Electrochromatography with Online Sample Stacking for Simultaneous and Sensitive Determination of Aminobenzoic Acid Isomers

A newly-developed method of complete separation and sensitive determination of o-, m-, and p-aminobenzoic acid isomers was achieved by combining open-tubular columns for capillary electrochromatography (OT-CEC) and online sample stacking. In this study, spherical gold nanoparticles were modified by a covalent attachment of mono-6-thio-β-cyclodextrin, and OT-CEC was formed by immobilizing cyclodextrin-modified gold nanoparticles (CD-AuNP) on prederivatized 3-mercaptopropyl-trimethoxysilane fused-silica capillaries. Based on the theory of moving chemical reaction boundary, effects of several important factors such as the pH and concentration of running buffer and the conditions of stacking analytes were optimized. The optimized separations were carried out in 58 mmol/L HAc buffer at pH 3.0 using a capillary coated with CD-AuNP, while the optimized concentration was carried out in 50 mmol/L disodium hydrogen phosphate (pH 9.5). The linear ranges for m-, p-, and o-aminobenzoic acid were from 5.0 × 10^?4–0.1, 5.0 × 10^?4–0.1 and 1.0 × 10^?4–0.1 mmol/L, respectively. And the detection limits (S/N = 3) were as low as 8.22 × 10^?5, 8.21 × 10^?5, and 3.76 × 10^?5 mmol/L for m-, p-, and o-aminobenzoic acid, respectively. The run-to-run, day-to-day, and column-to-column reproducibilities of migration time were satisfactory with relative standard deviation values of less than 4.5 % in all cases. This method was successfully used in determining procaine hydrochloride injection sample with recoveries in the range of 96.1–106.6 % and relative standard deviations less than 5.0 %.     

Application of semidifferential electroanalysis to anodic stripping voltammetry

A new voltammetric technique, Semidifferential electroanalysis, in which the semiderivative, e, of the current, i, is measured as a function of electrode potential, has been applied for detection in anodic stripping voltammetry. The semiderivative of the current is defined by [fx131-1.tif] Cd²⁺, Pb²⁺, and Tl⁺ in 0.1 M KNO₃ at different pH values were tested as samples on a hanging mercury drop working electrode. Symmetrical sharp peaks were observed for the re-dissolution processes of metal amalgams formed during pre-electrolysis at -1.0 V vs. SCE. The peak potentials of e vs. E curves for the above three amalgams agreed well with the literature values for d.c. polarographic half-wave potentials. The peak heights were proportional to the pre-electrolysis time up to about 5 min, to the potential scan rate in the range 60–160 mV s^-1, and to the concentrations of Cd²⁺, Pb²⁺, and Tl⁺ in the original solution in the range 10^-6–10^-9 M. The relative standard deviation for the determination of Cd²⁺ was about ±4% at the 2 × 10^-5 M level.     

Die bestimmung von alizarin s nach der anreicherung am stationären quecksilbertropfen und ihre anwendung zur fluoridanalyse

Traces of alizarin S can be concentrated on the stationary mercury electrode. The lower limit for the production of d.c. voltammograms is 5·10^-9M. The voltammetric spectrum of the dyestuff was examined by means of d.c. and a.c. polarographic techniques. An indirect voltammetric method for the determination of fluoride in the range 5·10^-7–5·10^-6M is suggested.