1, 2, and 3 were separated using a Waters Acquity UPLC BEH C18 column (2.1 x 100 mm, 1.7 µm particle size, Milford, MA) which was guarded by a Waters VanGuard BEH C18 precolumn (2.1 x 5 mm, 1.7 µM particle size, Milford, MA), maintained at 40°C, and eluted with linear gradients at a flow rate of 0.3 mL/min. Solvent A consisted of 10 mM ammonium formate in water at pH 4.0 and Solvent B consisted of acetonitrile with 0.1% formic acid. Starting from a mixture of 65% A and 35% B, B was increased from 35% to 90% in a linear gradient over 3 min, held at 90% for 1 min, and returned to initial conditions over 1 min. Total run time was 8 min. The injection volume for each sample was 2 µL, and the autosampler temperature was 4°C.