Hydrochloric acid hydrolysis of proteins and determination of tryptophan by reversed-phase high-performance liquid chromatography.

A simple method was developed for determination of tryptophan in proteins. Hydrolysis is achieved under reducing conditions, in 6 N hydrochloric acid containing 0.4% beta-mercaptoethanol, at 110 degrees C for 24 h. The phenylthiocarbamyl derivatives of the amino acids are separated by reversed-phase high-performance liquid chromatography, without any by-product interference. The recovery of tryptophan is complete. However, the method does not allow the determination of tryptophan in carbohydrate-rich biological samples.