Targeted Amino Acid Profiling by LC-MS

Amino acids and their metabolites were measured by LCMS as previously described (Lanza et al., 2010 (link)). Briefly, 20 μl of plasma was spiked with an internal standard solution consisting of isotopically labeled amino acids. The supernatant was immediately derivatized with 6‐aminoquinolyl‐N‐hydroxysuccinimidyl carbamate according to Waters' MassTrak kit. A 10‐point calibration standard curve underwent similar derivatization procedure after the addition of internal standards. Both derivatized standards and samples were analyzed on a Thermo Quantum Ultra triple quadrupole mass spectrometer coupled with a Waters Acquity liquid chromatography system. Data acquisition was done using select ion monitor (SRM) via positive electrospray condition. Concentrations of 42 analytes of each unknown were calculated against its perspective calibration curve.