The mass calibration was automatically performed every 10 injections using a positive calibration solution (AB SCIEX) via a calibration delivery system (CDS). Quality control was assured by (i) randomization of the sequence, (ii) injection of QC pool samples at the beginning and the end of the sequence and between each 10 actual samples, (iii) procedure blank analysis, and (iv) checking the peak shape and the intensity of spiked extraction internal standards (Mix 2 QReSS Kit) and the internal standard added prior to injection (Mix 1 QReSS Kit).