Ionization (MS 1) and fragmentation (MS 2) of each amino acid in tandem MS analysis.

<p>The data was collected as a 40 scan MCA (2 s/scan), i.e. each spectra is an accumulative result of 40 scans. The most abundant precursor and product ions for the amino acids were (M+H)⁺ and (M−COOH)⁺. The isobaric amino acids (e.g., Leu and Ile) have the similar and principal transition of <i>m/z</i> 132<b>→</b><i>m/z</i> 86. The transitions of <i>m/z</i> 132<b>→</b><i>m/z</i> 43 and <i>m/z</i> 132<b>→</b><i>m/z</i> 69 were observed to be characteristic of Leu and Ile, respectively. It was also observed that the transitions were not specific, and two minor signals of <i>m/z</i> 132<b>→</b><i>m/z</i> 69 and <i>m/z</i> 132<b>→</b><i>m/z</i> 43 occurred for Leu and Ile, respectively. Val, valine; Ile, isoleucine; Leu, leucine; Tyr, tyrosine; Phe, phenylalanine; M, molecular weight; m/z, mass-to-charge ratio; MS, mass spectrometry.