Chromatographic determination of cystine as cysteic acid

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Abstract
A method for detn. of the cystine plus cysteine content of proteins was based on oxidation of the protein by performic acid, hydrolysis by hydrochloric acid and chromatographic detn. of the resulting cysteic acid on columns of a basic ion-exchange resin (Dowex-2). The method can be used directly on products in which a high carbohydrate content may render other methods inapplicable, or in cases where the other uncertainties which apply to the stability of cysteine and cystine even under favorable hydrolytic conditions may render an alternative method desirable. The procedure was applied to analysis of foods and purified proteins.