Study On Detection Technology Of Pesticide Multi-residue In Citrus Based On Magnetic Dispersive Solid Phase Extraction

Citrus is one of the most popular fruits in the world.Citrus has a wide range of cultivation and abundant production in China.Fruit growers use a variety of different pesticides to improve the yield and quality of citrus,which will lead to excessive pesticide residues when improper use,and it will affect environmental safety,export trade and consumer health.Therefore,it is necessary to strictly monitor the use of pesticides in citrus to minimize the adverse effects of pesticide residues on the environment and the human body.For this reason,a stricter limit standard（GB2763-2019）has been formulated in China,which stipulates the maximum residue limits（MRLs）of pesticides in citrus fruits.There are many varieties of citrus fruits,and some varieties have a complex matrix.In order to detect pesticide residues in citrus,it is necessary to establish an easy,rapid and accurate multi-residue analysis and detection technology.In this study,a magnetic blend formed by graphitized carbon black（GCB）,magnetic nanoparticles（MNPS）,primary secondary amine（PSA）,and anhydrous magnesium sulfate（MgSO₄）were used as adsorbents,in order to achieve the purpose of obtaining a clean and clear supernatant without centrifugation again.This study optimizes the amount of MNPS,GCB,PSA and anhydrous MgSO₄ to achieve the best purification effect.And in order to achieve the best detection results,the instrument conditions of gas chromatography-tandem mass spectrometry（GC-MS/MS）and ultra-high performance liquid chromatography-tandem mass spectrometry（UPLC-MS/MS）were optimized.Finally,a magnetic dispersive solid-phase extraction-QuEChERS pretreatment technology was established,combined with GC-MS/MS and UPLC-MS/MS to rapidly detect multiple pesticide residues in mandarin,orange,lemon,pummelo and kumquat.Under the optimal conditions,the matrix effect of each pesticide in different citrus matrices,the linear range and the correlation coefficient（R²）of the method were investigated by adding standard recovery experiments in mandarin,orange,lemon,pummelo and kumquat,and accuracy,precision,and sensitivity were expressed by spiked recovery,relative standard deviation（RSD）,limit of quantification（LOQ）and limit of detection（LOD）,respectively.Among them,the three addition levels of gas chromatography tandem mass spectrometry were 0.01,0.05,and 0.1 mg/kg,the linear range was 0.01～0.5 mg/L,and the values of R² were all greater than 0.99.The average recovery rates（REs）of 75pesticides were in the range of 60.4%to 118.4%,the relative standard deviations（RSDs）ranged from 0.30%to 16%.The LOQs ranged from 10 to 20μg/kg,and the LODs ranged from 1 to 7μg/kg.Among the five citrus matrices,most of the pesticides belonged to the matrix enhancement effect.Compared with other pesticides,the matrix enhancement effect of monocrotophos,dimethoate,spirodiclofen and delta-HCH were stronger.The three addition levels of ultra-high performance liquid chromatography tandem mass spectrometry were 0.02,0.05,and 0.1 mg/kg,the linear range was 0.005～0.5 mg/L,and the values of R² were all greater than 0.99.The average REs of 83 pesticides were in the range of 61.3%to 115.9%,the RSDs ranged from 0.70%to 17.6%.The LOQs ranged from 10 to 20μg/kg,and the LODs ranged from 1 to 6μg/kg.Among the five citrus matrices,the matrix effect of most pesticides belonged to the matrix inhibitory effect.Compared with other pesticides,the matrix inhibitory effect of cartap hydrochloride,aldicarb,aldicarb-sulfone and oxamyl-oxime were stronger,and the matrix enhancement effect of lufenuron,fenbutatinoxide,abamectin and demeton-s-methylsulphon were stronger.This method has simple steps,low price,good accuracy,precision and sensitivity.It can accomplish the detection in a relatively short time,and is suitable for the detection of pesticide residues in a large number of fresh citrus fruit samples.In addition,a method of directly detecting glufosinate-ammonium and glyphosate without derivatization was also explored.Citrus samples were extracted with 0.5%formic acid water,purified by the mixture of GCB,PSA and MNPS,and combined with ultra-high performance liquid chromatography tandem mass spectrometry detection.The target compounds were separated by Waters Anionic Polar Pesticide,and eluted with 0.5%formic acid（FAC）water-0.5%FAC acetonitrile as the mobile phase.The four additive levels of the method were 0.02,0.05,0.5,and 1 mg/kg,the linear range was between 0.01 and 1 mg/L,and the correlation coefficients were≥0.9936.The average REs of glufosinate-ammonium were in the range of 76.1%to 108.5%,and the RSDs ranged from 0.4%to 11.3%,and the average REs of glyphosate were in the range of 78.3%to 108.8%,and the RSDs ranged from 1.8%to 11.4%.Among the five citrus matrices,two kinds of pesticides belonged to the matrix inhibitory effect.The LOQs for both herbicides were 20μg/kg,the LODs of glufosinate-ammonium ranged from 3 to 4μg/kg,and the LODs of glyphosate ranged from 1 to 5μg/kg.This method was quick and simple to operate,does not require derivatization,has good sensitivity and accuracy,and can be used to directly determine the residues of glufosinate-ammonium and glyphosate in samples.