Determination of Avermectin and Ivermectin Residues in Animal Origin Foods by LC-MS/MS Coupled with Online Solid Phase Extraction

A method of LC-MS/MS coupled with online solid phase extraction (SPE) for detemination of avermectin and ivermectin residues in animal origin foods was established by selection of SPE column and optimization of online eluting condition. The sample (2.50 g) was extracted with 5 mL of acetonitrile and 5mL of 0.15% (φ) triethanolamine solution, and the extract was purified by online clean-up with HySphere C₁₈ SPE column. The analytes were separated on ZORBAX SB C₁₈ column (2.1 mm×15 mm, 1.8 μm) with acetonitrile and 10 mmol·L^-1 ammonium acetate solution containing 0.2% (φ) formic acid as mobile phase in gradient elution. ESI⁺ and MRM were adopted in MS analysis. Linear relationships were found between the peak areas and the mass concentrations of avermectin and ivermectin both within 10 μg·L^-1, with the same lower limits of determination of 5.0 μg·kg^-1. Test for recovery were made by standard addition method in the samples of pork, beef and sausage, giving recovery rates ranged from 74.8% to 96.5%, with RSDs (n=6) within 11%.