Determination of quinclorac and quinclorac methyl ester in honey by online SPE-UPLC-MS/MS

A method employing online solid phase extraction (SPE) coupled to UPLC-MS/MS was developed for the determination of residues of the acid herbicide quinclorac plus its transformation product, quinclorac methyl ester, in honey. The analytical method involved dissolving the honey in a mixture of methanol:water followed by direct injection into a two-dimensional UPLC system which is used to perform an automated SPE cleanup on a reusable phenyl cartridge prior to the target analytes being transferred onto an analytical UPLC column for subsequent chromatographic separation followed by MS/MS detection. The limits of quantitation for quinclorac and quinclorac methyl ester in honey were both set at 0.5 µg kg−1 and the method detection limit was estimated to be 0.012 µg kg−1 for each compound. The working analytical range (0.5–100 µg kg−1) was validated by analysing a series of spiked replicate honey samples. The method was applied to the analysis of various honeys obtained from numerous different commercial sources. Quinclorac was detected in 9 out of 30 samples at concentrations ranging from 0.6 to 31.5 µg kg−1. Quinclorac methyl ester, which is estimated to be significantly more toxic than the parent herbicide itself, was not detected in any honey sample.

本研究开发了一种结合在线固相萃取（solid phase extraction，SPE）与超高效液相色谱-串联质谱（ultra performance liquid chromatography-tandem mass spectrometry，UPLC-MS/MS）的分析方法，用于测定蜂蜜中酸性除草剂二氯喹啉酸（quinclorac）及其代谢产物二氯喹啉酸甲酯（quinclorac methyl ester）的残留量。该分析方法的操作流程为：将蜂蜜样品溶解于甲醇-水混合溶剂中，随后直接进样至二维超高效液相色谱系统；该系统可先在可重复使用的苯基固相萃取柱上完成自动化的固相萃取净化步骤，再将目标分析物转移至分析用超高效液相色谱柱，进行后续色谱分离，最后通过串联质谱完成检测。蜂蜜中二氯喹啉酸与二氯喹啉酸甲酯的定量限均设定为0.5 µg kg⁻¹，两种化合物的方法检出限均约为0.012 µg kg⁻¹。通过对一系列重复加标蜂蜜样品进行分析，验证了该方法的工作分析范围为0.5~100 µg kg⁻¹。本方法被应用于多款不同商业渠道获取的蜂蜜样品的残留分析：在30份市售蜂蜜样品中，有9份检出二氯喹啉酸，检出浓度范围为0.6~31.5 µg kg⁻¹；而据估算毒性显著高于母体除草剂的二氯喹啉酸甲酯，在所有蜂蜜样品中均未被检出。