Commercially available LCMS grade acetonitrile was purchased from Fisher Scientific (Fair Lawn, NJ, USA). Ammonium formate and formic acid were purchased from Aldrich (Milwaukee, WI, USA). HPLC grade 18.2 MΩ water was produce using a Milli-Q water purification system (Millipore, Bedford, MA, USA). Pfizer proprietary compounds were used for this study.