THE DETERMINATION OF TRYPTOPHANE BY A MODIFIED GLYOXYLIC ACID METHOD EMPLOYING PHOTOELECTRIC COLORIMETRY

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Abstract
An accurate and reliable method for the estimation of tryptophane is described. It is based on the glyoxylic acid reaction, and involves the use of the Evelyn photoelectric colorimeter. The technique makes it possible to ascertain readily whether the color being measured is due only to tryptophane.The method has been applied to casein, of which, if necessary, only 25 mg. is required. The tryptophane determination is readily accomplished on a solution obtained by dissolving the casein in 10 or 20% sodium hydroxide or 5% formic acid by heating for a few minutes. With respect to alkali hydrolysis of casein under pressure, tryptophane is unstable in the sodium hydroxide hydrolysis, but is very stable in the baryta hydrolysis. The age and source of the casein are shown to be factors causing variations in the tryptophane content of different samples of casein, a variability which has been observed by a few previous workers.

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