um particle size, Phenomenex, Torrance, CA) with mobile phase consisting of water with 0.1% formic acid (mobile phase A) and acetonitrile with 0.1% formic acid (mobile phase B), running a linear gradient from 1 to 90% for 13 min, and then maintaining at 90% for 3 min, back to 1% in 1 min, and maintaining at this proportion for 7 min to equilibrate the column. The flow rate was set to 0.35 mL/min. The MS equipped with an H-ESI source was operated in the positive ionization mode with selected reaction monitoring (SRM). Ion spray voltage was 3.6 kV and ion transfer tube temperature was 325°C. The mass/charge (m/z) ratios monitored were 391.13/269.07, 391.13/287.00 for BACE1 inhibitor LY2886721 and 491.22/221.07, 491.22/249.07 for γ-Secretase inhibitor Compound E. A second transition of each analyte was used for confirmation purposes.
