It has been shown that the Sullivan reaction as a quantitative colorimetric method for the determination of cystine can be
considerably improved by better regulation of the conditions necessary
for optimum maximum colour development. This improvement has been brought about, chiefly by increasing the cyanide concentration and regulating the time interval between the adding of the napthoquinone reagent and the alkaline sulphite. It has been found that various substances interfere with the intensity of the final colour obtained. Thus other amino-acids, ammonium salts and sodium borate have been shown to retard or
inhibit the reaction, while sodium and potassium chlorides and sulphates have been found to exercise an acceleratory and intensifying action.
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