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. Author manuscript; available in PMC: 2020 Feb 1.
Published in final edited form as: Anal Biochem. 2018 Oct 26;566:1–9. doi: 10.1016/j.ab.2018.10.026

Figure 2. The GC/MS ion chromatograms and mass spectra of internal standard amino acids.

Figure 2.

A. Selective ion monitoring (SIM) using the precursor (M+.)-57 ions. Show is the total-ion-current (TIC) elution profile of internal standard stable-isotope labeled (IS) amino acids Gly+5, Met+3, and Ser+7. The chemical structures of the three IS amino acids are presented below the TIC. Red colored atoms are the stable-isotope labeled atoms.

B. The full-scan spectra of IS amino acids including Gly+5 (top panel), Met+3 (middle panel) and Ser+7 (bottom panel). While molecular ions are not present, major fragmented ions are M+.-15, M+.-57, M+.-85, and M+.-159. In this study, M+.-57 ions were used for quantification using the SIM mode.