Liquid chromatographic analysis of amino and imino acids in protein hydrolysates by post-column derivatization with o-phthalaldehyde and 3-mercaptopropionic acid.

A method for the simultaneous determination of imino and amino acids is reported. The method, based on the derivatization of amino acids, separated by ion-exchange chromatography, by reaction with alkaline hypochlorite and o-phthalaldehyde-3-mercaptopropionic acid, increases the sensitivity towards imino acids to the picomole level. The use of 3-mercaptopropionic acid gives intensely fluorescent derivatives and improves the stability of primary and secondary amino acid fluorophores towards oxidation. The accuracy and reproducibility of the method are increased by using three internal standards. The determination of all amino and imino acids present in protein hydrolysates, including tryptophan, in a single run is demonstrated.