Determination of 12 lipid soluble pesticides and three metabolites in raw milk by QuEChERS-high performance liquid chromatography-tandem mass spectrometry

A multi-residue analytical method for 12 lipid soluble pesticides and three metabolites in raw milk was established using QuEChERS sample preparation combined with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The target compounds included imazalil, cyproconazole, picoxystrobin, diflufenican, indoxacarb, lufenuron, etoxazol, fenpyroximate, clodinafop-propargyl and its metabolites clodinafop, trifloxystrobin and its metabolites trifloxystrobin acid, haloxyfop-etotyl, haloxyfop-methyl and their metabolite haloxyfop. The sample was extracted by 10 mL of 1% formic acid in acetonitrile, cleaned-up by 100 mg C₁₈ after being frozen for 5 h. The supernatant was filtered through a 0.22 μm organic membrane and determined by HPLC-MS/MS. The results showed that there were good linearity between the mass concentration and peak area of the 15 target analytes in the range of 0.01 to 1 mg/L, and the determination coefficient (R²) were higher than 0.9954. The average recoveries of the 15 target analytes in raw milk at the three spiked levels of 0.01, 0.1 and 1 mg/kg ranged from 87% to 109%, with relative standard deviations of 0.30% to 11% (n = 5). The limits of quantification (LOQ) of the method ranged from 0.001 to 0.01 mg/kg, and the limits of detection (LOD) were 0.0003-0.003 mg/kg. The validation results met the requirements of the pesticide residue analysis. The method was used to determine 30 samples from three main producing areas of raw milk in China. The results showed that the residue of etoxazol in 21 samples was greater than the LOD, but lower than the LOQ. The residue of etofenprox in the other sample was 0.0036 mg/kg. The residual amounts of the remaining 14 target compounds were all lower than their LODs. The method is suitable for the rapid determination of pesticide residues in raw milk, and provides a reference for the establishment of maximum residue limits (MRLs) of the 12 lipid soluble pesticides in raw milk and the dietary risk assessment in China.