A method was established for the simultaneous determination of seven avermectin (AVMs) residues, such as avermectin, ivermectin, doramectin, selamectin, eprinomectin, moxidectin and emamectin, in aquatic products using modified QuEChERS and high-performance liquid chromatography -tandem mass spectrometry (HPLC-MS/MS). The samples were extracted with 0.2% (v/v) ammoniate acetonitrile, and then 3 g of anhydrous magnesium sulfate and 2 g of anhydrous sodium sulfate were added to remove moisture and precipitate proteins. The samples were purified with 100 mg of C18 and 500 mg of anhydrous magnesium sulfate. The mobile phases comprised of acetonitrile (containing 0.1% (v/v) formic acid and 5 mmol/L ammonium acetate) and water (containing 0.1% (v/v) formic acid and 5 mmol/L ammonium acetate). The prepared samples were separated on a Varian Pursuit ULTRA C8 column (100 mm×2.0 mm, 2.8 μm) and determined using heated electrospray ionization (HESI) in the positive ion multiple reaction monitoring (MRM) mode. The analytes were quantified using external standard with the matrix-matched standard calibration curve method. The results showed that the solvent and matrix-matched standard curves for avermectin, ivermectin, doramectin, selamectin, eprinomectin and moxidectin in the range of 2-200 μg/L and for emamectin in the range of 0.2-20 μg/L were all linear, and the correlation coefficients (r) were ≥ 0.9972. The recoveries were 71.6%-112.8% with the relative standard deviations in the range of 4.7%-13.1%. The limits of quantification (LOQs) for avermectin, ivermectin, doramectin, selamectin, eprinomectin and moxidectin were all 5 μg/kg and for emamectin was 0.25 μg/kg. The present method is simple, repeatable, and suitable for the simultaneous determination of the residues of the seven avermectins in aquatic products.
