提出了固相萃取-超高液相色谱-串联质谱法同时测定植物油中百草枯和敌草快残留量的方法。取4.00 g样品,以10 mL正己烷为分散剂,涡旋1 min,加入20 mL体积比1∶1的0.1 mol·L^-1盐酸溶液-甲醇混合液,涡旋振荡提取20 min,离心5 min,弃去上层液体。取提取液15 mL经ProElut PXC固相萃取柱(用3 mL甲醇、3 mL水活化)净化,依次用3 mL水、3 mL甲醇淋洗,用3 mL体积比1∶1的2 mol·L^-1氯化铵溶液-甲醇混合液洗脱。流出液过0.22 μm尼龙膜,滤液采用超高效液相色谱-串联质谱法测定其中百草枯和敌草快的含量。以Dikma HILIC色谱柱为固定相,以不同体积比的10 mmol·L^-1甲酸铵溶液(pH 3.0)-乙腈的混合液为流动相进行梯度洗脱,质谱分析采用多反应监测(MRM)模式,外标法定量。结果表明,百草枯和敌草快标准曲线的线性范围分别为2.0~200.0 μg·L^-1、1.0~100.0 μg·L^-1,检出限(3S/N)分别为0.6,0.3 μg·kg^-1。按照标准加入法进行回收试验,回收率为80.5%~93.6%,测定值的相对标准偏差(n=6)均小于10%。方法用于30个植物油样品分析,仅在3个样品中检出敌草快,检出量最高达10.5 μg·kg^-1。

A method for determination of residues of paraquat and diquat in vegetable oil was proposed by ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) with solid phase extraction. 4.00 g of the sample was taken, 10 mL of n-hexane was added as dispersant, and the mixture was vortexed for 1 min. And then 20 mL of the mixture of 0.1 mol·L^-1 hydrochloric acid and methanol at volume ratio of 1∶1 was added. After vortex extraction for 20 min and centrifugation for 5 min, the upper liquid was discarded. 15 mL of the extract was taken and purified by ProElut PXC solid phase extraction column (activated with 3 mL of methanol and 3 mL of water), which was washed with 3 mL of water and 3 mL of methanol in turn and eluted with 3 mL of the mixture of 2 mol·L^-1 ammonium chloride solution and methanol at volume ratio of 1∶1. The effluent was filtered through a 0.22 μm nylon membrane, and paraquat and diquat in the filtrate were determined by UHPLC-MS/MS, with Dikma HILIC column as the stationary phase and mixtures of 10 mmol·L^-1 ammonium formate solution (pH 3.0) and acetonitrile at different volume ratios as the mobile phase for gradient elution. Multiple reaction monitoring (MRM) mode was adopted into MS analysis and external standard method was used for quantification. As shown by the results, linear ranges of the standard curves were 2.0-200.0 μg·L^-1 for paraquat and 1.0-100.0 μg·L^-1 for diquat, with detection limits (3S/N) of 0.6 μg·kg^-1 for paraquat and 0.3 μg·L^-1 for diquat, respectively. Test for recovery was made by the standard addition method, giving results in the range of 80.5%-93.6%, with RSDs (n=6) of the determined values less than 10%. The method was used for the analysis of 30 vegetable oil samples, and only diquat in 3 samples was detected, with the highest detection amount of 10.5 μg·kg^-1.