Thiosulphate In Gelatin Determination By Extraction And Polarography

A proportion of the thiosulphate in gelatin may be bound to the gelatin by cations so that all thiosulphate is not removed by aqueous extraction. After exchange of cations for sodium, a quantitative extraction of thiosulphate can be obtained. This conclusion rests on the following evidence:

(1) all thiosulphate added to deionized gelatin was extracted;

(2) exchange of cations in gelatin for sodium increased the yield of thiosulphate on extraction by an amount that varied between different gelatin samples;

(3) when anions (including thiosulphate) in gelatin were exchanged for chloride, a proportion of any further thiosulphate added remained bound to the gelatin apparently by the residual cations.

It was found that 200 p.p.m. of aluminium ion added to deionized gelatins reduced the fraction of added thiosulphate that could be extracted.

The amount of tetrathionate found was considerably less than the amount of thiosulphate and appears to have been formed during the extraction procedure.