Amino acid composition analysis has traditionally been conducted for protein quantitation and peptide structure prediction. Its use has also extended in recent years to the quantitation of such functional components as branched chain amino acids (BCAA). Previously, in Application News No. L432 and L437, we introduced examples of analysis of amino acids subjected to fluorescence derivatization using o-phthalaldehyde (OPA) using the SIL-30AC. Here, we introduce an example of fast analysis of amino acids in proteins.