Construction,analytical study and application of a new chloramine-t selective electrode

A chloramine-T (CAT) selective electrode with a liquid membrane of nickel batho-phenanthroline—chloramine-T dissolved in 2-nitro-p-cymene is described. The liquid membrane electrode exhibits rapid and near Nernstian response to chloramine-T activity from 10^-1 to 10^-4 M. The response is unaffected by pH in the range 5–9. Major interferences are penodate and perchlorate. In analytical applications, direct potentiometnc methods for the determination of chloramme-T, ascorbic acid, and arsenic(III), and a titnmetric method for ascorbic acid are described. Ascorbic acid and arsenic(IU) in the ranges 0.4–40 and 0.5–2 mg, respectively, can be determined with relative errors of 1–2%. The method has been applied to the determination of ascorbic acid in pharmaceutical preparations.     

Development and analytical applications of a new liquid-membrane 3,5-dinitrosalicylate-selective electrode

A 3,5-dinitrosalicylate (DNS)-selective electrode with a liquid membrane of either tetraphenyIphosphonium-DNSH dissolved in p-nitrocumene or dimethyldioctadecylammonium-DNSH dissolved in 1-decanol is described. The liquid membrane electrode exhibits rapid and near-Nemstian response to DNSH- activity from 10^-2 to 10^-5 M. The response is unaffected by pH in the range 2.5–6.5. The electrode has been successfully applied in the direct potentiometric titration of iron(III) and copper(II) with EDTA and in the indirect titrimetric determination of aluminium(III) and nickel(II). It is also useful in titrations of bulky quaternary cations such as cetyltrimethylammonium, cetylpyridinium and didodecyldimethylamnionium ions with DNSHNa.     

Potentiometric determination of some common alkaloids with a picrate-selective electrode

Potentiometric methods are described for the determination of alkaloids, based on the formation of insoluble alkaloid picrate salts, using a picrate ion-selective indicating electrode. Micro-amounts of strychnine, papaverine, quinine and cocaine were determined by direct potentiometry and titrimetrically, using Gran plots, with average errors of about 4% and 2%, respectively. The method was successfully applied to pharmaceutical preparations.     

Construction of an arginine enzyme electrode and determination of arginine in biological materials

The arginine electrode is based on a coupled enzymatic system consisting of arginase and urease with an ammonia gas sensor; conditions of immobilization are optimized. Arginine in the range 3 × 10^?5–3 × 10^?3 M gives a linear potential vs. log (concentration) plot with a response time of 5 min over the range specified. Several compounds structurally related to arginine do not interfere. The method is suitable for the determination of arginine in bovine insulin and human serum. Results compare well with values given in the literature or obtained by the conventional Sakaguchi method.     

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.     

Evaluation of a chloramine-T-selective electrode for catalytic titration of silver and mercury(II) based on iodide-catalyzed chloramine-T reactions

Semiautomatic methods are described for the catalytic titrimetric determination of microamounts of silver and mercury(II) using a chloramine-T-selective electrode as monitor. The methods are based on the inhibitory effect of Ag(I) and Hg(II) on the iodide-catalyzed chloramine-T-arsenite and chloramine-T-H₂O₂ reactions. Microamounts of silver in the range 0.2–200 μg (1 × 10⁻⁷−1 × 10⁻⁴ M) and of mercury(II) in the range 0.1–200 μg (2.5 × 10⁻⁸−5 × 10⁻⁵ M) were determined using the chloramine-T-As(III) indicator reaction. Mercury(II) in the range 4–2000 μg (1 × 10⁻⁶−5 × 10⁻⁴ M) was also determined using the chloramine-T-H₂O₂ indicator reaction. The accuracy and precision were in the range 0.1–1%.