Amino Acid Screen

Method Description

The Amino Acid Screen consists of three complementary analyses to quantify protein-bound amino acids. Acid Hydrolyzed Amino Acids: Samples are hydrolyzed in 6N HCl at 110°C to liberate amino acids from protein. Amino acids are separated by cation-exchange HPLC and quantified using post-column ninhydrin derivatization with UV/Vis detection. Cystine, methionine, and tryptophan are not quantified by this method due to degradation during acid hydrolysis. Tryptophan: Samples are hydrolyzed under alkaline conditions to preserve tryptophan prior to analysis by UPLC with fluorescence detection. Cystine and Methionine: Samples are oxidized with performic acid prior to acid hydrolysis to improve recovery of cystine and methionine. Analytes are quantified by cation-exchange HPLC with post-column fluorescence detection. Results are reported as cystine and methionine using molecular weight conversion factors. This method is not applicable to samples containing greater than 8% combined cystine and methionine. Results are reported on a dehydrated amino acid basis. Hydrated amino acid values may be provided upon request.