为解决农药残留测定时检测项目不全面、部分农药易吸附和降解等导致的回收率偏低的现象,提出了题示方法,并对净化条件和保护剂的种类及用量进行优化。样品经粉碎后,分取(3±0.05) g,加入1.0 mol·L^-1二硫苏糖醇溶液100 μL和1%(体积分数)乙酸溶液15 mL,浸泡30 min。加入15 mL乙腈,振荡5 min,加入质量比4∶1的无水硫酸镁和无水硫酸钠混合粉末7.5 g,振荡3 min,于冰浴中冷却10 min,离心5 min。分取上清液9 mL,用装有无水硫酸镁900 mg、N-丙基乙二胺300 mg、十八烷基硅烷键合硅胶(C₁₈)300 mg、硅胶300 mg的净化管净化,振荡5 min,离心5 min。分取上清液5 mL,于40℃氮吹浓缩至约0.4 mL,加入150 μL水,用乙腈稀释至1 mL,涡旋混匀后过0.22 μm滤膜,滤液进入超高效液相色谱仪,在ZORBAX Eclipse plus C₁₈色谱柱上用不同体积比的含0.1%(体积分数)甲酸的10 mmol·L^-1甲酸铵溶液和乙腈的混合溶液进行梯度洗脱,分离后的30种农药在串联质谱仪的电喷雾离子源正离子模式和多反应监测模式下检测,以基质匹配法定量。结果显示:以去除了石墨化碳黑(GCB)的QuEChERS吸附剂作净化剂可有效降低氯磺隆、胺苯磺隆、甲磺隆和杀虫脒的吸附损失,以二硫苏糖醇作保护剂可降低内吸磷、甲拌磷砜和苯线磷等有机磷类农药的降解损失;30种农药可在20 min内完成分离,标准曲线的线性范围为10~150 μg·L^-1,检出限为0.001~0.005 mg·kg^-1;对空白样品进行加标回收试验,回收率为81.3%~110%,测定值的相对标准偏差(n=6)为1.3%~11%;方法用于实际样品分析,仅在一份样品中检出灭线磷,检出量为0.012 mg·kg^-1。

To resolve problem of low recovery caused by incomplete testing items, easy adsorption and degradation of some pesticides in the determination of pesticide residues, the title method was proposed, and the purified condition, type and amount of protective reagent were optimized. The sample was crushed, and an aliquot (3 g±0.05 g) was taken and mixed with 100 μL of 1.0 mol·L^-1 dithiothreitol solution and 15 mL of 1% (φ) acetic acid solution for soaking for 30 min. After 15 mL of acetonitrile was added, the mixture was oscillated for 5 min. Mixed powder (7.5 g) composed of anhydrous magnesium sulfate and anhydrous sodium sulfate at mass ratio of 4∶1 was added, and the mixture was oscillated for 3 min, cooled in ice bath for 10 min, and centrifuged for 5 min. An aliquot (9 mL) of the supernatant was taken and purified with a purification tube containing 900 mg of anhydrous magnesium sulfate, 300 mg of N-propylethylenediamine, 300 mg of C₁₈ and 300 mg of silica. After oscillation for 5 min and centrifugation for 5 min, 5 mL of the supernatant was concentrated to about 0.4 mL with nitrogen-blowing at 40 ℃, mixed with 150 μL of water, and diluted to 1 mL with acetonitrile. After vortexing, the above solution was passed through a 0.22 μm filtrate membrane, and the filtrate was introduced into ultra-high performance liquid chromatograph. Gradient elution was performed on ZORBAX Eclipse plus C₁₈ column with mixed solution of acetonitrile and 10 mmol·L^-1 ammonium formate solution containing 0.1% (φ) formic acid at different volume ratios, and the 30 pesticides separated were detected in positive ion mode of electrospray ion source and multiple reaction monitoring mode in tandem mass spectrometer, and quantitatively analyzed by matrix-matched method. As shown by results, the QuEChERS adsorbents without GCB could reduce the adsorption loss of chlorsulfuron, ethametsulfuron, metsulfuron-methyl and chlordimeform. Using dithiothreitol as protective reagent, the degradation loss of systox, phorate sulfone and fenamiphos was also reduced. Thirty pesticides could be separated within 20 min, and linear ranges of standard curves were found in the range of 10-150 μg·L^-1, with detection limits in the range of 0.001-0.005 mg·kg^-1. Test for recovery was made by standard addition method on the blank sample, giving recoveries in the range of 81.3%-110%, and RSDs (n=6) of the determined values ranged from 1.3% to 11%. The proposed method was applied to the analysis of the 3 batches of actual samples, and fenamiphos was found in one of these samples, with detection amount of 0.012 mg·kg^-1.