Analyses were performed using an ultrahigh-performance LC-MS system consisting of a Dionex Ultimate 5000 liquid chromatograph (Thermo Fisher Scientific, Waltham, MA, USA) and an ultrahigh-resolution accurate-mass (HRAM) quadrupole time-of-flight (Q-ToF) mass spectrometer (IMPACT II; Bruker Daltonik, MA, USA). For chromatographic separation by gradient elution, an Acclaim RSLC 120 C18 column (2.2 μm, 2.1 × 100 mm; Thermo Fisher Scientific, Waltham, MA, USA) and a combination of mobile phases (Phase A, 0.1% formic acid; Phase B, methanol) were used. Gradient elution started at 2% Phase B (0-1 min) and continued at 100% Phase B after 18 min, followed by a wash (up to 22.5 min) and a 10-min equilibration of 2% Phase A. The column temperature was controlled at 35 °C and the mobile phase flow rate was set at 250 µL min -1 . The sample injection volume was 5 µL. Samples were measured by electrospray ionization in positive mode and spectra were acquired with a mass resolution of > 60,000 and a scan rate of 1 Hz over a mass range of 60-1,500 m/z. Data were stored and processed in centroid mode.