Study On Pretreatment Technology Of Pesticide Residues In Farmland Soil

In this paper,31 kinds of different polar pesticides banned or restricted by the state wereselected.Ethylacetate/water-ammoniumacetatesystemand acetonitrile/water-ammonium sulfate system were used to extract pesticides.Ultra-high pressure liquid chromatography-mass spectrometry was used to simultaneously detect various pesticides in soil.Simultaneous analysis methods of various pesticides in soil were established.Five farmland soils were tested by this method,and the practical application effect was good.This paper is divided into there parts:(1)31 pesticides were divided into two parts according to their polarity:weak polarity pesticides and medium polarity pesticides.The detection methods of 23 weak polarity pesticides by liquid chromatography tandem mass spectrometry and 8 medium polarity pesticides by liquid chromatography tandem mass spectrometry were established respectively.Under the mode of electrospray ion source,positive ion scanning(ESI~+)and multi reaction monitoring(MRM),the parameters of each mass spectrum(collision gas:4psi;air curtain gas:25 psi;atomizing gas:45 psi;auxiliary gas:50 psi;ion source temperature:450~oC;ionization voltage:5000.0V;pesticide removal voltage,taper hole voltage,impact voltage)and liquid chromatography parameters(mobile phase composition)(Acetonitrile,water),column temperature(40 ~oC)and gradient elution procedure were selected to establish an efficient,rapid and accurate instrumental analysis method.The 23 weak polar pesticides showed good linear relationship in the linear range of 0.1 ug/L to 100 ug/L,and the correlation coefficients were between 0.996 and 1.000.The detection limit is as low as 0.0024 ng/mL~1.24 ng/mL.The precision of the instrument is good,RSD is less than 7.6%.The linear relationships of eight moderately polar pesticides were good in the range of 0.1 ug/L to 100 ug/L,and the correlation coefficients were between 0.997 and 1.000.The detection limit is as low as 0.0007ng/mL~0.128 ng/mL.The precision of the instrument is good,RSD is less than 9.0%.The31 pesticide detection methods established in this study have the advantages of high selectivity,high sensitivity and high detection efficiency.(2)The pretreatment methods of 23 weak polarity pesticides and 8 medium polarity pesticides were established respectively.The extraction effect of organic reagents such as acetonitrile,acetone,ethyl acetate and trichloromethane combined with ammonium acetate and ammonium sulfate on pesticides was investigated.The factors affecting the extraction rate and distribution coefficient of pesticides in the system were studied by single factor experiment.The optimal pretreatment level was selected by orthogonal design,range analysis and variance analysis.The optimum extraction conditions of 23weak polar pesticides were as follows:ethyl acetate 70%,ammonium acetate 3.000 g,centrifugation for 5 minutes,and standing at room temperature(25~oC)for 15 minutes.The extraction efficiency of 23 weak polar pesticides ranged from 92.80%to 100.0%.The optimum extraction conditions for 8 kinds of moderately polar pesticides were as follows:80%acetonitrile,0.500 g ammonium sulfate,5 minutes centrifugation and 15 minutes at20~oC.The extraction efficiency of 8 kinds of moderately polar pesticides ranged from93.20%to 99.96%.(3)According to the polarity of pesticides,this chapter is divided into two parts:weak polarity and medium polarity.The simultaneous detection methods of pesticide residues in soil are established and methodological evaluation is carried out.Ethyl acetate/water-ammonium acetate extraction was used as pretreatment method and UPLC-MS/MS was used to detect 23 weak polar pesticide residues in soil.The linear relationship of the method was good,and the correlation coefficient was greater than0.997.The quantitative limit of 23 weak polar pesticide residues was as low as 0.005ng/g~5.09 ng/g.The recoveries of farmland soils in Zhifu District of Yantai City were between62.40%and114.00%withRSDlessthan10%.Using acetonitrile/water-ammoniumsulfateextractionaspretreatmentmethodand UPLC-MS/MS to detect 8 kinds of moderately polar pesticide residues in soil.The linear relationship of the method was good,and the correlation coefficients were all greater than0.998.The quantitative limit of eight moderately polar pesticide residues was as low as0.0414 ng/g~0.506 ng/g.The recoveries of farmland soils in Zhifu District of Yantai City ranged from 70.5%to 102.0%with RSD less than 8.0%.It can completely meet the detection requirements of trace pesticides in soil.The method has been applied to the detection of farmland soil in five areas and has good applicability.Experiments show that there are different levels of pesticide residues in various regions,and the problem of pesticide pollution can not be underestimated.