气相色谱-三重四极杆质谱法测定植物源性食品中棉隆及其代谢物异硫氰酸甲酯残留

Determination of dazomet and its metabolite methyl isothiocyanate residues in plant-derived foods by gas chromatography-triple quadrupole mass spectrometry

基于气相色谱-三重四极杆质谱建立了同时快速测定植物源性食品中棉隆及其代谢物异硫氰酸甲酯残留量的方法。对样品前处理及色谱条件进行了优化,蔬菜、水果、谷物、坚果、茶叶和香辛料样品经乙酸乙酯提取,离心后上清液经乙二胺-N-丙基硅烷化硅胶、石墨化炭黑、十八烷基键合硅胶和无水硫酸镁分散固相萃取净化,经DB-17MS色谱柱(30 m×0.25 mm×0.25μm)分离,采用EI源,在多反应监测(MRM)模式下检测,基质匹配外标法定量。在优化实验条件下,目标化合物在0.005~1 mg/L范围内的线性关系良好,相关系数均大于0.99,方法定量限为0.01 mg/kg。空白样品在4个添加水平下的平均回收率为74.2%~117.2%,相对标准偏差(n=6)为2.8%~9.0%,方法的准确度和精密度符合农药残留测定要求。应用建立的方法对实验室日常样品大白菜、韭菜、豇豆、油麦菜、茄子、姜、芹菜、马铃薯、橙、猕猴桃、西红柿、辣椒、大米、茶叶、杏仁和孜然各6个进行检测,均未检出目标物。该方法具有操作简单、快速、灵敏、准确的特点,解决了已有方法中需采用两种前处理方法、两套设备进行检测的不足,能满足植物源食品中棉隆及其代谢物异硫氰酸甲酯的检测要求。

Dazomet is a kind of crystal solid that is stable at room temperature and acts as a fumigant.It is commonly used to control soil fungi,as an insecticide,and in sterilization and weeding.It can effectively kill root-knot nematodes,soil pests,weeds,and many soil-borne disease-causing organisms,to provide clean and healthy soil.Dazomet slowly decomposes and releases methyl isothiocyanate,methylamine,carbon disulfide,and hydrogen sulfide in acidic soil,and diffuses upward through the spaces in the soil to kill contact organisms.When agricultural crops are planted in soil treated with cotton wool,the residues in the grown crop can cause harm to human body when consumed.To ensure the quality and safety of food crops,it is important to develop a detection method for dazomet and its metabolites in plant-derived foods.Hence,in this study,a rapid and simultaneous determination method was developed for dazomet and its metabolite methyl isothiocyanate residues in plant-derived foods by gas chromatography-triple quadrupole mass spectrometry(GC-MS/MS).The sample pretreatment and chromatographic conditions were optimized in the experiment.Subsequently,dazomet and its metabolite methyl isothiocyanate residues in vegetables,fruits,grains,nuts,tea,and spices were extracted with ethyl acetate,and purified using graphitized carbon,a primary-secondary amine,stearyl-bonded silica gel,and anhydrous magnesium sulfate as dispersive solid-phase extraction sorbents.After centrifugation and filtration,the target compounds were analyzed in the multiple reaction monitoring(MRM)mode by GC-MS/MS,and quantified by matrix matching external standard method.The matrix effects of the samples were also evaluated.The matrix effect was found to be in the range of 2.5%to 13.6%for methyl isothiocyanate in 16 matrices.As this matrix effect was weak,there was no need for compensatory measures.In contrast,the matrix effect of dazomet in 16 matrices was in the range of 240.3%to 331.2%.This matrix effect was strong and required compensation.Finally,a matrix matching calibration method was used to compensate the matrix effects.The relative matrix effects of other tested substrates were analyzed using lettuce as the representative substrate;it was found that all showed weak matrix effects.Therefore,the use of lettuce as a representative matrix to prepare a matrix standard curve can effectively correct the matrix effects of dazomet and methyl isothiocyanate in other substrates.Under the optimal conditions,the calibration curves were linear in the range of 0.005-1 mg/L with correlation coefficients higher than 0.99.Recovery tests were conducted by adding mixed standards to blank samples at four levels.The recoveries were in the range of 74.2%-117.2%with relative standard deviations(RSDs,n=6)of 2.8%-9.0%.The limits of quantification(LOQs)of dazomet and methyl isothiocyanate were 0.01 mg/kg.The accuracy and precision of this method met the requirements of pesticide residue determination.The established method was used to detect dazomet and its metabolite methyl isothiocyanate residues in six samples of Chinese cabbage,Chinese chives,cowpea,lettuce,eggplant,ginger,celery,potato,orange,kiwifruit,tomato,chili,rice,tea,almond,and Cuminum cyminum L.in the laboratory,and nothing was detected.The method is simple,rapid,and sensitive;overcomes the shortcomings of existing methods that require two pretreatment steps and two sets of equipment;and meets the requirements for the detection of dazomet and its metabolite methyl isothiocyanate residues in plant-derived foods.