High-performance liquid chromatography of tryptophan and other amino acids in hydrochloric acid hydrolysates

Tryptamine [3-(2-aminoethyl)indole] as an additive to 6 M HCl largely prevented the decomposition of tryptophan in proteins, and also in gas-phase hydrolysis, using a Pico-Tag Work Station, at 145°C for 4 h. This procedure proved to be excellent for amino acid analysis using conventional high-performance liquid chromatography with derivatization with phenyl isothiocyanate. The recovery of tryptophan from model solutions and from proteins was 80–98%. The results proved to be as good as any other obtained by the analysis of special alkaline or organic acid hydrolysates, most of which are suitable exclusively for the determination of tryptophan. The most important advantage of tryptamine was that it did not affect the quantitative recovery of other amino acids of proteins, as shown by the composition of lysozyme hydrolysates obtained in the absence and presence of various amounts of tryptamine. The reproducibility of the measurements was 3.7% (relative standard deviation) or less.