title: Determination of the protein and free amino acid content in a sample using o-phthalaldehyde and N-acetyl-L-cysteine.
abstract: A spectrophotometric method is proposed for determining the protein content in a sample after total acid hydrolysis. In the procedure, free amino acids are caused to react with o-phthalaldehyde and N-acetyl-L-cysteine at pH 9.5, using isoleucine as the reference compound. Correction factors are used to take into account the differences between the molar absorptivities of the amino acid isoindoles and the recoveries of the amino acids after the hydrolysis treatment. The limit of detection was in the range 40-50 micrograms of protein, and the recoveries were usually 101 +/- 3% with a coefficient of variation lower than 4%. The free amino acid content in a partially hydrolysed protein was also determined.
authors: Departamento de Química Analítica, Facultad de Química, Universitat de Valencia, Spain.
authors: M J
authors: MJ
authors: Medina Hernández
authors: R M
authors: RM
authors: Villanueva Camañas
authors: E
authors: E
authors: Monfort Cuenca
authors: M C
authors: MC
authors: García Alvarez-Coque
mesh_terms: D000111:Acetylcysteine; D000596:Amino Acids / Q000032:analysis*; D006868:Hydrolysis; D011506:Proteins / Q000032:analysis*; D013053:Spectrophotometry; D009764:o-Phthalaldehyde
chemical_list: D000596:Amino Acids; D011506:Proteins; D009764:o-Phthalaldehyde; D000111:Acetylcysteine