Spectrophotometric analytical technique for tryptophan and tyrosine

Acid hydrolysis of an aqueous mixture of tryptophan and serine yields a spectrophotometrically constant product suitable for a quantitative analysis of tryptophan. Tschesche claims to have produced pyruvic acid from the acid hydrolysis of serine. Therefore, the direct hydrolysis of pyruvic acid with tryptophan should produce the same spectrophotometrically constant product found by the former procedure . Tschesche's hydrolysis of serine produced a dubious product and the tryptophan-pyruvate product was found to be unsuitable for a spectrophotometric quantitative technique.