HPLC analyses were carried out using an Agilent 1290 HPLC systemconnected toan Agilent 6490 triple quadrupole MS/MS via a Jetstream electrospray ionization (ESI) source (Agilent Technolo-gies). Experiments used a reverse-phase Poroshell 120 EC-C18 column (150 mm long, 3.0 mm i.d., 2.7 mm particle size; Agilent Technologies) maintained at 40 C. Sample aliquots (20 ml) were injected into 0.4 ml/min flow of the mobile phase consisting of (A) 2 mmol/l ammonium acetate in ultrapure water and (B) 2 mmol/l ammonium acetate in methanol. The initial proportion of 20% (B) was linearly ramped to 60% (B) at 2 min, then linearly ramped to 100% (B) at 10 min and finally held at 100% (B) for 2 min. The system was equilibrated using the initial composition for at least 4 min prior to each analysis.