The gradient elution was carried out by
starting from 35% to 65% acetonitrile in 5 min, held for 3 min,
and then back to 35% acetonitrile in 5 min, held for 3 min to equilibrate
the column. The flow rate of the mobile phase was maintained
at 1.0 mL min1. The eluate was split and introduced into
the MS detector at a flow rate of 0.2 mL min1. ESI-MS/MS detection
was performed in the positive mode, and the source dependent
parameters were as follows: curtain gas, N2 (33 psi);
collision gas, N2 (medium); gas 1, N2 (55 psi); gas 2, N2 (50 psi);
ion spray voltage, 4500 V; temperature, 400 C. Table 1 summarised
the parameters employed in this study after optimisation.