Separations were conducted on a reversed-phase column (Phenomenex, Kinetex F5, 2.6µm 100 Å, 100 x 4.6 mm) at a flow rate of 0.7 mL/min at 40°C. Mobile phase A was 0.1% formic acid in water and mobile phase B was 0.1% formic acid in methanol. The samples were analyzed on a SCIEX 6500+ QTRAP under negative ESI mode. The total run time was 5.5 min. Eight calibration standards and three quality control (LQC, MQC and HQC) samples were used for quantification.