2.6 Experimental instruments and reagents
AB 5500/6500 Q-trap mass spectrometer (AB SCIEX); Agilent 1290 Infinity LC ultra-high pressure liquid chromatograph (Agilent); low temperature high speed centrifuge (Eppendorf 5430R); Chromatographic column: Waters, ACQUITY UPLC BEH Amide 1.7μm, 2.1mm × 100 mm Waters, ACQUITY UPLC BEH C18 1.7μm, 2.1mm × 100mm column; Acetonitrile (Merck, 1499230-935); Ammonium acetate (Sigma, 70221); Methanol (Fisher, A456-4); ammonia (Sigma, 221228); Ammonium formate (Sigma, 70221); Formic acid (Sigma, 00940); Isotope standard (Isotope Laboratories).