Kinetic study and analytical application of the iodate-arsenite reaction in strongly acidic solutions

The iodate-arsenite reaction in strongly acidic solutions was studied by stopped-flow spectrophotometric techniques. The molar absorptivity of iodine and the activation energy of the reaction were determined. A method for determining arsenite was developed on the basis of this reaction. The method was checked in the concentration range 5.0·10^-4–1.0·10^-2M, the mean error being about 3%.     

A sensitive spot test for the detection of sodium based on the fluorescence of sodium-zinc-uranyl acetate

A modification of the zinc-uranyl acetate spot test for the detection of small amounts (down to 0.1 μg) of sodium is described based on the intense fluorescence of the crystalline mixed sodium-zinc-uranyl acetate, under the incidence of uv light.     

Microdetermination of molybdenum by an automatic reaction-rate method

An automatic reaction-rate method is described for the microdetermination of molybdenum; the method is based on the hydrogen peroxide-iodide reaction which is catalyzed by molybdenum. The effect of reagent concentrations was studied and the maximum tolerable amounts of interfering ions were determined. Procedures for the determination of 0.01–0.15 μg and 0.1–1.0 μg molybdenum per milliliter are given ; 0.036–2.5 μg of molybdenum could be determined with relative errors of about 2%.     

Kinetic detection of the end-point in titrations involving slow reactions Direct titration of polyhydroxy-compounds with periodate

A new titration technique is described in which the end-point is determined by measuring the relative reaction rate of the titration reaction. This technique is adequate for rather slow reactions where conventional direct titrations are not applicable. The titrations are done automatically under microcomputer control. The efficiency of this technique is demonstrated with direct titrations of certain polyhydroxy-compounds with standard periodate solution. Ethylene glycol and propylene glycol (0.05-0.3 mmole), glycerol (0.06-0.17 mmole) and mannitol (0.01-0.03 mmole) were determined with average relative errors of 0.1-0.3%.     

Catalytic microdetermination of chromium(VI)

An automatic spectrophotometric kinetic method for the microdetermination of chromium(VI) is described, based on catalysis of the hydrogen peroxide-iodide reaction. The time required for the reaction to produce a small fixed amount of tri-iodide is measured automatically, and is proportional to the chromium(VI) concentration. Maximum tolerable amounts of various interfering ions were investigated. From 0.6 to 3.0 mug of chromium(VI) can be determined with relative errors of 1-2%, with measuring times of 10-50 sec.     

Kinetic identification and determination of certain carbohydrates with a periodate-sensitive perchlorate-selective electrode

The reactions between periodate and carbohydrates are easily monitored with a perchlorate-selective electrode as a periodate sensor. The relative reaction rate constant of each carbohydrate compared to glucose is introduced as a new characteristic constant, the “periodate index”, which could be related to the molecular configuration. Since appreciable differences are observed between the “periodate index” values of various carbohydrates, this constant can be used for the identification of 20-mg amounts of single pure compounds. An automatic potentiometric reaction rate method is described and shown to be simple, rapid and accurate for the determination of glucose. Amounts of glucose in the range 7–54 mg were determined in 20–140 s with precision and relative errors of about 0.4 and 0.8 %, respectively.     

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

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

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Maßanalytische Bestimmung von Jodid, Hexacyanoferrat(II), Thioharnstoff, kanonischen Schaummitteln und von Pikrat mit einer pikrationenselektiven Elektrode

Zusammenfassung Methoden zur halbautomatischen Fällungstitration von Jodid, Hexacyanoferrat (II), Sulfid und Sulfid-Thioharnstoff-Gemischen mit Silbernitrat sowie von medizinisch bedeutenden quartären Ammoniumverbindungen mit Natriumpikrat und von Pikrationen mit Tetraphenylarsoniumchlorid unter Verwendung einer pikrationenselektiven Elektrode wurden beschrieben. Halbmikro- bzw. Mikromengen der genannten Stoffe wurden mit einem rel. Fehler und einer rel. Standardabweichung von 1–2% bestimmt.

     

Potentiometric titration of organic cations with sodium tetraphenylborate and a liquid-membrane tetraphenylborate ion-selective electrode

Simple potentiometric titrations are described for the determination of various organic cations (usually 5–25 μ mol) with 0.01 M sodium tetraphenylborate. A liquid-membrane electrode with tetrapentylammonium tetraphenyiborate dissolved in 4-nitro-m-xylene as liquid ion-exchanger is used successfully in the semi-automatic titration of quaternary ammonium compounds, cationic surfactants, alkaloids and other substances of pharmaceutical importance which are precipitated by tetraphenyiborate. Analysis of pharmaceutical preparations gave satisfactory results.