G. Aravamudan

The determination of thiourea using chloramine-T

Abstract Chloramine-T oxidises thiourea quantitatively to urea and sulphate ion in neutral and alkaline media. The oxidation is completed within 2 min, even with a very small excess of the oxidant. Urea and ammonium ion do not interfere if the oxidation is carried out in an alkaline medium.

Stability characteristics of aqueous chloramine-T solutions

Aqueous chloramine-T solutions in strongly alkaline medium are quite stable even up to 60 degrees . In 0.2-2 M sulphuric or perchloric acid at 25-30 degrees , there is no loss in titre, but in hydrochloric acid solutions > 0-5M, there is a loss in titre which increases with increase in hydrochloric acid concentration. This is ascribed to oxidation of chloride to chlorine. In the pH range 2.65-5.65 there is a small but reproducible loss in oxidative titre which is maximal at pH 4.7. This is ascribed to side-reactions occurring during partial disproportionation of monochloramine-T to dichloramine-T and p-toluenesulphonamide.

Fluorimetric determination of trace quantities of mercury as an ion-association complex with rhodamine 6G in the presence of iodide

A procedure for the indirect fluorimetric determination of mercury(II) is described, based on selective extraction of the ion-association complex formed between triiodomercurate(II) and Rhodamine 6G and subsequent release of the fluorescent Rhodamine 6G. The calibration curve is linear up to 1 ppm of mercury(II). The few interferences are easily overcome.

Estimation of dimethylsulphoxide with chloramine-T

A rapid and accurate method for the estimation of dimethyl-sulphoxide has been developed based on its oxidation to dimethyl-sulphone at room temperature by chloramine-T at pH 4-4.5. The effect of variables such as the pH, the mode of addition of reagents and the concentration of chloride ion on the extent and nature of oxidation has been studied and optimal conditons for analytical determination of dimethylsulphoxide derived.

Spectrophotometric determination of tellurium in trace quantities by use of an ion-association complex.

The formation of an ion-association complex by the interaction of iodotellurate(IV) with cetyltrimethylammonium bromide is used as the basis of an extractive procedure to determine tellurium in the range 2.5-12.5 mug in a final aqueous phase volume of 20 ml. The method is simple, reliable and sensitive. Selectivity is achieved by separation of tellurium on aluminium hydroxide as collector.

Oxidimetric determination of triphenylphosphine.

A method for the determination of triphenylphosphine based on its oxidation to phosphine oxide by iodine or chloramine-T in acid medium in presence of benzene or carbon tetrachloride is described. The oxidation is completed within 2 min and the analytical values are accurate to within 0.5%. The method is applicable to determination of triphenylphosphine in its metal complexes.

The determination of thiomalic acid

Abstract The extent of oxidation of thiomalic acid by iodine, potassium iodate, potassium bromate, potassium periodate and chloramine-T depends on alkalinity, temperature and duration of reaction. Therefore these oxidants do not provide a satisfactory method for the determination of thiomalic acid.

Determination of trace quantities of selenium by indirect atomic-absorption spectrophotometry

The selenium(IV)-iodide interaction in acid medium, leading to the liberation of iodine, has been utilized for the indirect determination of selenium by atomic-absorption spectrophotometry (AAS). The iodine is extracted into benzene and subsequently reductively stripped into an aqueous solution of ascorbic acid. After extraction of the resulting iodide as tris(1,10-phenanthroline)cadmium(II) iodide into nitrobenzene, the cadmium content of the organic extract is determined by AAS. Beers law is applicable up to 0.75 ppm of selenium. The few interferences are readily overcome. The chemical yield in the system is about 80% overall.

Iron(II)-chloramine-T reaction.

When a large excess of the oxidant is used in the iron(II)-chloramine-T reaction at pH 2.56-5.6 the amount of oxidant consumed is well above the stoichiometric amount required to oxidize iron(II) to iron(III). This has been attributed to the formation and subsequent behaviour of free radicals during the reaction. The formation of free radicals has been experimentally demonstrated. They apparently dimerize to give products of the type R-NCl-NCl-R (R = CH(3)C(6)H(4)SO(2)), which are further oxidized by chloramine-T. The dimerized species liberate iodine very slowly from acidified potassium iodide. This explanation satisfactorily accounts for the observed extent and rate of destruction of excess of chloramine-T in presence of small amounts of Fe(II) or bromide at pH 2.65-4.70. The storage of chloramine-T in metal containers might cause extensive destruction of the oxidant by a similar free radical mechanism and should be avoided.

Oxidimetric determination of sulphides

Hypoiodite oxidises sulphides much more rapidly than does iodate under comparable experimental conditions. A procedure is reported for the determination of soluble and insoluble sulphides by oxidation to sulphate with hypoiodite. This is an improvement over Bethges iodate method.