Establishment And Application Of Gas Chromatography Method In Determination Of Organophosphorus Pesticide Multiresidues In Vegetables

Objective:In order to detecting pesticide residues of organophosphorus in vegetables,a fast, simple and accurate capillary gas chromatography method was established.This method fit for detection of large quantity of specimen and may detect 11 kinds of pesticide in quality and quantity simultaneously.With this method,pesticide residues of organophosphorus were analyzed to understand the condition of pesticide residues in edible vegetables in the market of Qingpu,Shanghai.Methods:1.Kinds of pesticide residues:6 kinds of forbidden organophosphorus pesticide residues were tested,including methamidophos,phorate,demeton,monocrotophos, parathion-methyl and parathion.Besides these,5 kinds of popular organophosphorus pesticide residues,dichlorvos,chlorpyrifos,dimethoate,malathion and omethoate, were analyzed.2.Instruments and conditions:CP-3800 gas chromatography(VARIAN Corporation,America),pulsed flame photometric detector(PFPD),CP-8400 automatic sampler(VARIAN Corporation,America),chromatographic column (SUPELCO EQUITY-1701 and Agilent HP-5),injection temperature 160℃, specimen size 2μl,split sampling(split ratio 1:10),detector temperature 300℃.3.Method optimization:Pretreatment was optimized from the aspects of quantity of agents and kinds of absorbent agent.Chromatographic conditions were optimized from the aspects of chromatographic column used in analyses, programmed-temperature control,carrier gas flow,working conditions of PFPD.4.Pretreatment of specimen:Centrifugated after extraction by acetonitrile and blending by excessive vibration with NaCl and MgCl₂.Acetonitrile in upper layer was extracted and conserved in Teflon centrifugal tube.After vibration and centrifuge,supernatant was transferred into inject bottle of gas chromatography for test.5.Method control quality:external standard method was applied for control of method quality.The specification curve of each pesticides was drafted respectively. Detection limit was obtained after stepwise dilution of standard series's smallest density.Cucumber was taken as example.Recovery experiment was performed with different size of standard,and the percent recovery,the precision and method detection limit were calculated.6.Specimen:From December 2008 to April 2009,specimen were collected randomly form Agriculture Industry and Commerce supermarket and 5 primary food market including Chengdong vegetable market,Qinghua vegetable market, Sanyuanhe vegetable market,Jiejinggang vegetable market and Xiayanghu vegetable market.The collected specimen included solanaceae,cucurbits and vegetables, Chinese cabbage,green leafy vegetables and beans.Results:1.In pretreatment,10.0g of specimen homogenate was transfer into 50 ml Teflon centrifugal tube and centrifugated at the speed 5000 r/mim after extraction by 10 ml acetonitrile and blending with NaCl and MgCl₂ by excessive vibration for 1 min.2 ml acetonitrile in upper layer was extracted and conserved in Teflon centrifugal tube with 50 mg PSA and 300 mg MgSO₄.If chlorophyl of specimen was too much,10 mg GCB power was added into the supernatant.After vibration and centrifuge,1 ml supernatant was transferred into inject bottle of gas chromatography for test.In addition,microwave was needed for Chinese chive before pretreatment.Microwave was needed for Chinese chive,middle temperature for 30 sec.2.In the study,each pesticide was identified by both chromatographic column, 1701 and HP-5 column.The programmed-temperature used in 1701 column was as following:40℃,2 min→40℃/min→220℃→7℃/min→260℃,and in HP-5 column was 40℃,2 min→20℃/min→260℃.Carrier gas flow applied was 1 mL/min.The detector in the study was PFPD in which the hydrogen flow was 14 mL/min and integrating time was 4 msec.3.Each kind of organophosphorus pesticide was separated well on specific chromatographic column with nice standard curve.The related coefficient was from 0.9974 to 0.9999,and MDL was from 0.02 mg/kg to 0.05 mg/kg.The percent recovery of cucumber was 76.1%to 105.8%,and relative standard deviation was from 3.4%to 8.9%.4.From December 2008 to April 2009,304 pieces of specimen were analyzed, among which organophosphorus was found in 13 pieces of specimen,4.27%of all the specimen.In these,there occurred 5 pieces of specimen,1.64%of all specimen, whose concentration of pesticide were over the permitted limit.No organophosphorus was found in the 30 pieces specimen collected from the supermarket.In the specimen collected from vegetable market,3 pieces of Chinese cabbage specimen were found positive with chlorpyrifos,among which 1 piece of specimen was over the permitted limit.In green leafy vegetables specimen,2 pieces were positive with methamidophos, and 7 pieces were positive with chlorpyrifos.Among these,4 pieces were over the permitted limit.One piece of solanaceae specimen was found positive with chlorpyrifos,too.No specimen in cucurbits and vegetables and beans was found positive.Conclusion:1.Pre-treatment was simple and fast,and could be performed in multisample with less time,effort and cost.Quantity of GCB power added to specimen should be controlled due to its absorption to organophosphorus.GCB power should be less than 10 mg even if there were much pigment.2.Each pesticide was well identified with the optimized conditions.3.Forbidden pesticide of high toxicity was found in vegetables in Qingpu district, Shanghai.Most of positive specimen belonged to leaf vegetables.On the whole, pesticide residues of organophosphorus in vegetables in Qingpu district,the condition in Shanghai was light.