Dispersive Liquid-liquid Microextraction Method And Its Application To24Pesticide Residues

Dispersive liquid-liquid microextraction (DLLME) technique, as one form of liquid phasemicroextraction (LPME), has gained great attention since its introduction, due to the obviousadvantages, such as simplicity of operation, rapid extraction and less harm to the environment. So far,DLLME method has been used in the fields of agriculture, medicine, environment, et al., and there arealso reports on pesticide residue analysis. But it needs to be deeply studied on the multi-pesticides incomplex matrix. Therefore, this article studied DLLME method for24pesticides, belonging to OPP,OCP and PYR, in agricultural products, and established a DLLME pretreatment method for24pesticideresidues in pear samples and QuEChERS-DLLME for rice samples, respectively. In addition, theproposed methods were examined in5fruit samples, and millet, corn samples. The main researchcontents and results were as follows:(1) Investigation on the main factors affecting DLLME performance. A DLLME pretreatmentmethod was established for24pesticides in pear samples, by studying the influence of differentextractive and dispersive solvent combinations, extractive solvent volume, dispersive solvent volume,salt addition and extraction time on extraction efficiency, on the basis of optimized GC-ECD detectionmethod. Results indicated that under the condition of90μL CTC as extractive solvent,0.5mL ACN asdispersive solvent, extraction time1min and centrifugation time5min at5000rpm, good recoveries of24pesticides were obtained at three spiked levels (10μg/kg,20μg/kg, and100μg/kg), ranging from75.4%to118.1%and relative standard deviation (RSD) was between0.6%~9.0%. Based on3and10times of signal to noise (S/N), limits of detection (LODs) and limits of quantification (LOQs) were0.05μg/kg~5.05μg/kg and0.16μg/kg~16.67μg/kg, respectively.(2) On the basis of previous research, QuEChERS-DLLME for rice samples were developed bycombing QuEChERS and DLLME these two pretreatment methods. Recoveries were good(71.16%~118.97%), and RSD was no larger than8.37%, with LODs and LOQs varying between0.36μg/kg~7.15μg/kg and1.18μg/kg~23.58μg/kg, respectively.(3) Application of DLLME and QuEChERS-DLLME techniques to fruit and cereal samples. Theabove two methods were used to apple, tomato, pineapple, strawberry, grape and millet, corn samples.Experimental results showed that the average recoveries for fruit samples were in the range of71.9%~118.62%(except captan and folpet) for three spiked levels, with relative standard deviation(RSD) less than9.5%; cereal samples were spiked at three levels, namely50μg/kg,100μg/kg, and500μg/kg, and average recoveries of millet samples were between60.3%~119.73%(except captan andfolpet), with RSD in the range of0.20%~7.92%; average recoveries of corn samples were between70.18%~127.33%(except captan and folpet), with RSD no larger than9.69%. Furthermore, analysisresults of the real samples indicated that different concentrations of different kinds of pesticide residueswere detected, but all under the MRL set by China. The established pretreatment method was easy to operate, employed less organic solvent, offeringreliable experimental results and good reproducibility. Thus it met the requirements of modern pesticideresidue analysis, and was suitable for the analysis of22pesticide residues in both simple and complexmatrix.