Reaserach On Pretreatment Of Organophosphorus Pesticide Residues In Vegetables By Gas Chromatography

At present,most of the testing institutions in China conduct quantitative detection and analysis of organophosphorus pesticide residues in vegetables adopting NY/T761-2008 Pesticide multiresidue screen methods for determination of organophosphorus pesticides,organochlorine pesticides,pyrethroid pesticides and carbamate pesticedes in vegetables and fruits.In practical application,it was found that the method used acetone solvent to prepare pesticide standard solution to quantify the sample,ignoring the influence of matrix effect on the detection result.In addition,the method is easy to cause low recovery of some thermal instability and water-soluble pesticides in practical testing,which affects the accuracy of the test results.In this study,we studied the pretreatment methods for the detection of twelve organophosphorus pesticide residues in vegetables,analyzed the main causes of problems,changed the conditions affecting the recovery rate of pesticides with different properties,and improved the pretreatment methods to make the test results more accurate and reliable.It is conducive to improving the testing level of the regulatory staff and thus indirectly plays a role in controlling the amount of pesticide residues,which is of great significance for ensuring the safety of agricultural products and enhancing the competitiveness of China's international market.In this study,the chromatograms of the standard solution and the acetone pure solvent standard solution were tested by using different matrix preparations,and the effect of matrix effect on the pesticide recovery rate was summarized.By changing the water bath temperature and the ratio of the extracted reagent amount to the sample amount in the pretreatment process of organophosphorus pesticide residue detection,and comparing the recovery rate of watersoluble pesticides and heat-labile pesticides before and after the change of the conditions,and then select the best conditions to improve and verify the pre-processing conditions.The improved method was used to detect different varieties of vegetables in the market,and the results were statistically analyzed to summarize the types and reasons of vegetables easily exceeding the standards.The experiment result shows:(1)The sample is quantified by using a blank matrix matching the sample to be tested,which can compensate the influences of the matrix effect.The temperature of the pretreatment water bath is lowered from 80 ° C to 65 ° C,and the ratio of the amount of the extracted reagent to the sample amount is increased from 2:1 to 2.5:1,which can improve the recovery rate of the thermally unstable pesticide and the water-soluble pesticide,and improve the accuracy of test results.(2)In order to verify the accuracy of the improved method,spiked recovery experiments were performed in four different vegetable matrices.The average spiked recoveries of twelve organophosphorus pesticides at three levels of addition(six parallel)ranged from 70.0% to 119.3%,indicating that the method is quantitatively accurate.The relative standard deviation(RSD)is 0.8%-12.4%.The results show that the detection method is sensitive and accurate,and meets the requirements of pesticide detection methods.It is applicable to the analysis of 12 organophosphorus pesticide residues in vegetables.(3)200 samples of commercially available vegetables were randomly selected and tested.The results showed that the detection rate and over-standard rate of pesticide residues in green leafy vegetables were the highest,and there are banned pesticides.The relevant departments should clarify the monitoring focus and further strengthen management.