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  • Title: [Determination of 118 pesticide residues in dried wolfberry by gas chromatography-triple quadrupole mass spectrometry in dynamic multiple reaction monitoring mode].
    Author: Yang Z, Zhang W, Wu F, Wang X, Xu X.
    Journal: Se Pu; 2021 Jun; 39(6):659-669. PubMed ID: 34227327.
    Abstract:
    Wolfberry fruit is very popular among consumers because it is rich in nutrients. However, it is vulnerable to diseases caused by insect pest feeding and microbial pathogen infection. Pesticide application is the main approach for controlling wolfberry disease; however, various concerns have been raised regarding chemical residues in foodstuffs and consequent environmental contamination. Matrix interference is a significant challenge in trace analysis. Chromatography, coupled with MS techniques with high sensitivity and selectivity, proved to be a powerful tool for the detection of multi-pesticide residues in complex matrices. The traditional MRM mode has been gradually replaced by the dynamic MRM (dMRM) mode, which could dynamically allocate the retention time window of each target pesticide, significantly adjust the loading cycle time of multiple compounds, and improve the analysis efficiency. The QuEChERS pretreatment method, based on dispersive solid-phase extraction, has been widely used in the detection of pesticide residues in food because it is simple and rapid. In this study, a robust and high-throughput method was established for the simultaneous determination of 118 pesticide residues in wolfberry using the modified QuEChERS method, combined with gas chromatography-triple quadrupole mass spectrometry in dMRM mode. The optimal pretreatment method was determined by comparing the recovery rates obtained with different volumes of added water (5, 10, 15, and 20 mL), different extraction solvents (acetone, n-hexane, acetonitrile, and acetonitrile containing 0.1% formic acid), different extraction temperatures (normal temperature, -18 ℃ for 10 min and 20 min), water absorbent (anhydrous magnesium sulfate), and purification with primary secondary amine (PSA) and octadecylsilane (C18). The results showed that 5 g samples were rehydrated with 10 mL ultrapure water, extracted with 10 mL acetonitrile, frozen at -18 ℃ for 10 min, partitioned with buffer system salt package containing 4.0 g anhydrous magnesium sulfate, 1.0 g sodium chloride, 1.0 g sodium citrate, and 0.5 g disodium citrate, purified up with 800 mg MgSO4, 150 mg PSA, and 150 mg C18. Pesticides were separated on a capillary column HP-5MS UI (30 m×0.25 mm×0.25 μm), and quantified by a matrix-matched external standard method. The results showed that the 118 pesticides exhibited good linearity in the range from 20 to 640 μg/L, with correlation coefficients R2≥0.9923. The limits of detection and quantification were 0.006-28.344 μg/kg and 0.021-94.480 μg/kg, respectively. The average recoveries at four spiked levels of 0.01, 0.04, 0.10, and 0.20 mg/kg were in the range of 64.97%-126.21%, with relative standard deviations (RSDs) of 0.69%-18.86% (n=6). The results of the matrix effect showed that 82% of the pesticides exhibited matrix enhancement effects, while others showed matrix inhibition effects. In addition, 9% of the pesticides showed a strong matrix effect, while others showed moderate or weak matrix effects. The matrix effects could be reduced by the matrix-matched standard curve method. The proposed method was employed for the analysis of 10 real samples purchased from local markets. The results demonstrated that pesticides were detected in all the samples, 22 pesticides were detected in total, and 3-12 pesticides were found in a single sample. Chlorpyrifos, fipronil, cypermethrin, pyridaben, and difenoconazole were detected at high detection rates. The captan content in a batch of samples was 1.4066 mg/kg. Thus, the optimized method is simple, fast, accurate, and reliable, and it is suitable for the routine detection and rapid screening of the multi-pesticide residues in wolfberry. 枸杞中丰富的营养物质深受广大消费者喜爱,但也极易受到病虫侵害,农药残留问题引起了人们的广泛关注。基质干扰是微量分析的一个难点,高灵敏度和高选择性的色谱-串联质谱技术是复杂基质中微量分析强有力的工具,动态扫描监测模式的优越性逐渐取代传统的多反应监测扫描模式,简便、快速、省时的QuEChERS前处理方法已被广泛应用于食品的农药残留检测中。采用改良QuEChERS法结合动态多反应监测模式(dMRM),建立了同时检测枸杞干果中118种农药残留的气相色谱-三重四极杆质谱分析方法。实验比较了不同加水量、提取溶剂、提取过程中温度提取条件,以及无水硫酸镁吸水剂、乙二胺-N-丙基硅烷化硅胶PSA、十八烷基硅烷键合硅胶C18净化填料添加量时农药的回收率,确定出最优前处理方法。结果表明,5 g样品经10 mL超纯水复水,用10 mL乙腈浸提,于-18 ℃冷冻10 min后,用缓冲体系盐包提取后,经800 mg无水硫酸镁、150 mg PSA、150 mg C18混合填料净化,基质匹配外标法定量。118种农药在一定范围内线性关系良好,相关系数R2≥0.9923,检出限和定量限分别为0.006~28.344 μg/kg和0.021~94.480 μg/kg, 4个添加水平的回收率为64.97%~126.21%, RSDs均小于19%(n=6)。基质效应考察结果表明,82%的农药呈现为基质增强效应,其他为基质抑制效应;9%的农药表现为强基质效应,其他为中等或弱基质效应;采用基质匹配标准曲线校正,可有效降低基质效应的影响。应用建立的方法测定10批枸杞样品,全部样品有农药检出,共检出农药22种。该方法操作简便快速,准确可靠,适用于枸杞干果中农药多残留的日常检测和快速筛查。
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