positive ionization mode (ESI+). Best results were obtained with a capillary
voltage of 3 kV, source block temperature of 130 8C, and desolvatation gas
(nitrogen) heated to 400 8C and delivered at 800 L/h. No cone gas was used.
Collision cell pressure was 3 106 bar of argon. Data were recorded in the
selected reaction monitoring (SRM) mode. A post-column infusion system was
used to optimize ionization for all target compounds and internal standards. The
mobile phase (pH 3.0 ammonium formate buffer/acetonitrile, 50/50) was
delivered into the electrospray interface at a rate of 0.2 mL/min, while analyte
at 10 mg/L was being infused post-column through a dead volume tee, by using
a syringe pump at 10 mL/min. The precursor ions, product ions, cone voltage
and collision energy obtained are presented in Table 1. The MS method was
divided in three SRM functions to obtain at least 18 acquisition points per peak.
Data acquisition, peak integration and calculation were interfaced to a
computer workstation running MassLynx NT 4.0 and QuanLynx 4.0 software.