Research On A Modified QuEChERS Method For GC-MS Determination Of Pesticides In Rice

China is not only the biggest country in rice production,but also the largest one in rice consumption.Jiangsu province is a main region of rice consumption and production in China.Rice is more than 63 percent of the staple food consumption.It is also an integral ingredient of many nonstaple food such as rice cakes,desserts and alcoholic beverages. The annual average consumption of rice in China is over 140kg.Rice is generally cultivated in areas with a warm and humid environment and thus its cultivation attracts a proliferation of insects.In order to prevent pest and raise crop yield,at present the maior effective measurement is chemical control.The in rice paddy is usually with 2 or 3 categories each time.In local area,more than 10 times of pesticides application are carried out in the whole growth cycle of rice..Calculated by the aforesaid amount, one-kilogram rice is probably sprayed one-gram pesticides.Illegal or irrational pesticides application result in environment pollution and chemical residues in edible rice products. In comparion to the advantage of pesticides in raising crop yield,their hazards to human health and environment are more profound.We lag behind some of the foreign countries in detection techniques of pesticide residues.In domestic most test methods on the analysis of pesticide residues in food are based on chromatographic techniques,such as GC-FPD/ECD and LC-UV.In the present study,rice was selected as a research object and the main aim is to set up the mass spectrum library of 21 pesticides standard,improve QuEChERS sample preparation method and chromatographic conditions in order to set up the chromatographic detection method of 13 pesticides and study the degradation laws of 12 pesticides added into rice. The principal contents are as follows:(1) The mass-spectrum library of 21 pesticides standard by means of scanning in the mass range of 50- 450.These pesticides include 5 herbicides,14 insecticides and 2 bactericides.Of which,herbicides are butachior,pretilachlor,bentazone,propanil and molinate;insecticides are thiocyclam,bisultap,cartap,dichlovos,pirimiphos-methyl, fenitrothion,malathion,phenthoate,chlorpyrifos,benfuracarb,carbofuran,isoprocarb and deltamethrin;bactericides are isoprothiolane and ediphenphos.On this basis,using GC-MS qualitative analysis of analytes was studied,involved 3 carbamates insecticides,which are benfuracarb,carbofuran and isoprocarb,thiocyclam,bisultap and cartap of nereistoxin insecticides,and bentazone of organic heterocyclic herbicide;Quantitative analysis of 13 analytes simultaneously was validated,containing dichlovos,molinate,isoprocarb, pirimiphos-methyl,malathion,fenitrothion,propanil,phenthoate,butachlor,pretilachlor, isoprothiolane,ediphenphos and deltamethrin.(2) The optimized separation condition of gas chromatogramphy and mass spectrometry achieved the complete separation for 21 pesticides with one injection.The DB-1701 fused-silica capillary analysis column was selected(30m×0.25mm×0.25μm).GC separation condition was as follows:Helium was as carrier gas at a constant flow at 1.2mL/min.The temperature of the injection port was 290℃and a volume of 1μL was injected in splitless mode with solvent delay 5.0min.The temperature program was used as follows:initial temperature,80℃held for 1.5min,then increased at the rate of 30℃/min to 130℃,5℃/min to 250℃,and 10℃/min to 300℃,and then maintaining this temperature for 5min.The mass spectrometric parameters were:autotune,electron multiplier voltage 1700V,mass spectrometer transfer temperature 280℃,ion source temperature 230℃, electron ionization mode with an ionizing energy of 70eV,when performing selected ion monitoring,scanning from m/z 50 to 450.(3) QuEChERS sample preparation method was modified.Only one sorbent of 100mgPSA could achieve the least matrix interference.During the extraction procedure temperature 4 degrees could improve the recovery of thermal instability of pesticides.As far as Concentrated way is concerned,Vacuum drying was better than Rotary Evaporator. The minimum detection limit of the method was decreased by increasing the volume of sample(10g) and concentrating 3 times extraction.The modified QuEChERS is rapid, simple,easy-to-use,low-cost,less use of solvents,low-pollution,environmentally friendly and requirement of less space and equipment.It is superior to the sample preparation of the GB/T 19649-2006.(4) The method for the determination of 13 pesticides in rice using modified QuEChERS sample preparation method and GC-MS-SIM was developed.The 13 pesticides were dichlovos,molinate,isoprocarb,pirimiphos-methyl,malathion, fenitrothion,propanil,phenthoate,butachlor,pretilachlor,isoprothiolane,ediphenphos and deltamethrin.The MQLs were from 0.011mg/kg to 0.345mg/kg.The linear ranges from 0.01mg/kg to 1.8mg/kg covered MQL and maximum residue limits(MRLs) with excellent correlation coefficient mostly above 0.999.Most fortified recoveries were from 70%to 110%and relative standard deviations(RSD) of all pesticides were less than 20%.In conclusion,this method shows that it meet the requirements analysis and could be as a reference for day-to-day monitor of pesticide residues in rice.(5) Simulated sample spiked with amount of 2 times MRLs of 12 pesticides was determined by the modified QuEChERS sample preparation method combined GC-MS-SIM after Storage at room temperature.The 12 pesticides include dichlovos, molinate,isoprocarb,pirimiphos-methyl,malathion,fenitrothion,propanil,phenthoate, butachlor,pretilachlor,isoprothiolane,and deltamethrin.The simulated sample was determined on the week,the first week,the second week,the fourth week and the 20th week respectively.According to the analysis results,12 pesticides degradation regression modes were set up.Except propanil follows S mode and deltamethrin follows exponentiall mode,the others were estimated power modes.The half-life periods of 12 pesticides degradation were forecast by the degradeation modes.The most half-life periods were less than 30 days,but that of butachlor,pretilachlor,isoprothiolane,isoprocarb and deltamethrin exceed 30 days.Some pesticides such as isoprocarb and deltamethrin break down slowly.Since the two kinds of pesticide residues exceed,if stored for a valid period, not fit for human consumption.As a general rule,organophosphorous pesticide degraded quickly.It is recommended that rice in season should be edible safely one month after harvest.