Mass spectrometric conditions Mass spectrometry was performed on a Waters Xevo®TQ tan-dem quadrupole mass spectrometer equipped with electrosprayionization (ESI) source. The conditions of ESI source were as fol-lows: Source temperature 150◦C; Desolvation gas temperature,550◦C; Desolvation gas (N2) flow rate, 850 L h−1; Cone gas (N2) flowrate, 50 L h−1; Capillary voltage, 4.00 kV; Collision gas (Ar) flow rate,0.15 mL min−1. All the six compounds were analyzed in positive ESI mode and multiple-reaction monitoring (MRM) mode was selected for quantification.