Tryptophan decomposes under normal hydrolysis conditions. Therefore, tryptophan analysis can be carried out after hydrolysis in 3 M mercaptoethanesulfonic acid. Because tryptophan residues are scarce in protein, tryptophan analysis requires a larger amount of sample material than for other amino acids. Tryptophan analysis is carried out only when requested. Alternatively, the tryptophan content can also be determined by UV-spectroscopy.
Spectroscopic determination is advantageous in that the material can be recovered for other studies.