“…Subsequently, plasma samples were deproteinized with acetonitrile at a final concentration of 80%. The samples were then subjected to precolumn derivatization followed by high‐performance liquid chromatography (HPLC)‐electrospray ionization (ESI)‐mass spectrometry (MS) for AA quantification, which was performed as previously described (Shimbo et al, 2009a; Shimbo et al, 2009b; Yoshida et al, 2015). The following 21 AAs were quantified: alanine (Ala), alpha‐aminobutyric acid (α‐ABA), arginine (Arg), asparagine (Asn), citrulline (Cit), glutamate (Glu), glutamine (Gln), glycine (Gly), histidine (His), isoleucine (Ile), leucine (Leu), lysine (Lys), methionine (Met), ornithine (Orn), phenylalanine (Phe), proline (Pro), serine (Ser), threonine (Thr), tryptophan (Trp), tyrosine (Tyr), and valine (Val).…”