Multi-modal LC-MS/MS Characterization

Each sample was analyzed using three separate LC-MS/MS methods using two different LC systems (Thermo Scientific ICS-5000+ ion chromatography and Thermo Ultimate 3000). Each was coupled directly to a Q-Exactive HF Hybrid Quadrupole-Orbitrap mass spectrometer with a HESI II electrospray ionization source (Thermo Scientific, San Jose, CA). Full details for each method are provided in the “Supplementary information” section (Supplementary Methods). Briefly, for method 1, anion-exchange chromatography coupled with mass spectrometry (IC-MS/MS) was performed as recently published [31 (link)]. Reversed phase C18 column analysis was performed for both methods 2 and 3. For method 2, the samples were used underivatized (same as in method 1) [31 (link)], while for method 3, samples were derivatized prior to analysis using a modified version of the Waters AccQ-Tag method designed for amino-acid analysis [35 (link)].