Multiresidue Determination Of Pesticides In Vegetables And Fruits By Gas Chromatography With Mass Spectrometry And Examination On Matrix Effects

It is an important job for governments to build and perfect the test and monitoring system and relevant standards of pesticide residue analysis. Development of the fast, effective, sensitive multi-residue detection methods of pesticides is a hot research task. Now a rapid, sensitive, high-efficient analytical method for determination of multiclass pesticide residues by GC-MS is proposed and it meets the trend of modern analytical method for pesticide residues. Accurate quantification and identification of susceptive analyte can be seriously affected due to matrix-induced enhancement or suppression effect that commonly encountered in the gas chromatographic analysis of pesticides in produce or food. But there is little research on this at present. Relative systematic researches are performed and measures of accurate quantitative analysis are proposed in this paper.A multi-residue method was developed for rapid determination of 52 pesticides and their isomers in vegetables and fruits by GC-MS in selective ion monitoring mode with the aid of analyte protectant. Pesticides were extracted from samples with acetonitrile and the extract was cleaned up using dispersed primary-secondary amine (PSA) absorbent. Good linear and lower limits of detection were obtained, the linear range are between 0.01~1.00 mg/L, correlation coefficients are better than 0.99, and the detection limits is between 0.0002~0.0094 mg/kg except for deltamethrin and iprodione. All compounds spiked in grape have mean recoveries of 73.5 %~110.6 % (0.5 mg/kg level) and the relative standard deviation(RSD) values are all less than 11.6 % except for chlorothalonil, and mean recoveries of 81.8 %~119.5 % are achieved in celery and the RSD is between 0.8 % and 17.6 %.It was demonstrated that applying protectants could provide a more accurate quantitation and compensate "matrix-induced chromatographic response enhancement" in gas chromatography-mass spectrum (GC-MS) analysis, thus increase reliability of test. Effects of 3 compounds used as protectants on compensation for matrix effect are evaluated in mixed matrix and comparison with matrix-matched standard are made. The matrix-induced error for most pesticides has been shown to be avoided by adding 3-Ethoxy-l,2-propanediol (20 mg/mL) and D-Sorbitol (1 mg/mL) before injection, especially for acephate, omethoate, methamidophos, paraoxon etc ; nevertheless, it cannot be compensated for op'-DDT and pp'-DDT which show certain matrix suppression effect.The concepts of the "relative matrix effect" and "absolute matrix effect" in assessment of matrix-introdued effect in pesticide residues analysis are introduced, and relative matrix effect about 45 pesticides in 22 produces are evaluated. Results indicated that pesticides show different variability in certain extent in relative response between different matrixes. Certain pesticides are matrix-dependent such as chlorothalonil, paraoxon, deltamethrin, methamidophos, acephate etc, among them, chlorothalonil have better relative response in acidic matrixes (as orange, tomato, grape, kiwi fruit) but have serious suppression in scallion, onion, garlic, leek, lotus root etc. In like wise, the acidic matrixes can prevent transforming from deltamethrin to its isomer. In addition, some pesticides, such as methyl-chlorpyrifos, chlorpyrifos, methyl-pirimiphos, malathion, op'-DDE, etc., show relative high stability in various matrixes.