Analysis of biological fluid amino acids with an amino acid analyzer usually targets 41 amino acid components. In recent years, however, the study of metabolic errors in newborns, for example, has advanced significantly giving rise to the demand for analysis of more amino acids that induce metabolic errors. To cope with this, new methodology has been developed for the simultaneous analysis of an additional 12 amino acids involved in metabolic errors besides the usual 41 components, thus analyzing 53 components total. In addition, the amino acids related to specific metabolic errors can now be analyzed in a short time.