A Dionex Ultimate 3000 (Thermo Scientific) LC was coupled to the front end of a custom-built hybrid linear ion trap FT-ICR MS equipped with a 21 T superconducting magnet. CuLs were separated using a 30 min gradient from 95/5% to 5/95% solvent A/B (solvent A = 5 mM ammonium formate in water, solvent B = 5 mM ammonium formate in MeOH) on a Zorbax SB-C18 column (40 o C; 0.5 x 150 mm, 5 µm particles, Agilent) at 40 µL min -1 . The eluent was coupled to a HESI source operated in positive mode (4.5 kV). The inlet capillary and source heater temperatures were set to 350 °C and 75 °C, and sheath and auxiliary gas flow rates were set to 5 and 3 (arbitrary units). MS 1 spectra were collected from 150 to 1500 m/z. All spectra were collected with a resolution of 1,200,000 at 400 m/z, an automatic gain control (AGC) target of 1x10 6 charges, and a maximum ion injection time of 1500 ms. The achieved mass spectral resolving power at m/z 200 was ~1,700,000-3,000,000 across the LC gradient.