Further study on gas phase acid hydrolysis of protein: improvement of recoveries for tryptophan, tyrosine, and methionine.

A novel method for vapor phase acid hydrolysis of protein suitable for quantitative analysis of tryptophan is presented. The hydrolysis is carried out in vapor of a mixture made of 7 M HCl, 10% trifluoroacetic acid, and 20% thioglycolic acid in the presence of indole. Reasonably good recoveries of common amino acids, including tryptophan (above 75%), were achieved.