x 2.1 mm, 1.6 μm particles, 100 Å pores) with the column temperature kept at 30 °C. The eluent flow was 0.3 μL min -1 and consisted of LC-MS grade H2O acidified with 0.1 % formic acid (solution A) and LC-MS grade acetonitrile with 0.1 % formic acid (solution B). The gradient was: 0-3 min: 95 % A; 3-14 min linear ramp to 95 % B; 14-16 min hold at 95 % B; 16 min return to 95 % A; and 22 min hold in preparation for the next run. Mass spectra were obtained with the m/z range of 100-750 in the negative ion mode. The parameters of the heated electrospray ionization (HESI) ion source settings of the Orbitrap were: 2.5 kV spray voltage, 300 °C probe heater temperature, 320 °C capillary temperature, S-Lens ion funnel RF level 30, 50 units of sheath gas (nitrogen) flow, 10 units of auxiliary gas (nitrogen) flow, and 1 unit of spare gas (nitrogen) flow.