The analytes retained on the cartridge were eluted with 3 mL acetonitrile at a flow rate of 0.5mL min_1.
The elution solution was filtered through a 0.25 μm membrane. Finally, 20 μL of the eluate was injected into the HPLC for analysis.
After extraction, the cartridge was washed sequentially with 9 mL of methanol, 9 mLof acetone and 9 mL of water.
Then, the cartridge was used for the next extraction.