In a typical SPE procedure, an Oasis HLB cartridge (10 mg,
Waters, USA) was conditioned with 2.0 mL acetonitrile and
10.0 mL Milli-Q water, successively. Then the aqueous extract obtained
in MASE or SE procedure was loaded onto the cartridge,
and 2.0 mL of 5% acetonitrile aqueous solution was applied to the
cartridge in a wash step. Afterwards 1.0 mL acetonitrile were used
to elute the target compounds. The eluate was filtered through a
0.45 lm microporous membrane for subsequent HPLC–MS/MS
analysis.