Study On The Determination Of Chlorfluazuron Residue In Cabbage, Chinese Cabbage, Tomato And Capsicum

Chlorfluazuron is a promising benzoylurea insecticide,used for the control of insects attacking a wide range of crops,especially fruits and vegetables. The compound acts as powerful growth regulators which inhibit the synthesis of cuticle chitin in target pests,causing death or abortive development.Study on the determination of chlorfluazuron residuein cabbage,Chinese cabbage,tomato and capsicum is crucial for proper assessment of exposure to chlorfluazuron in vegetables.Firstly,the determination condition of chlorfluazuron by high performance liquid chromatography was optimized;secondly,sample preparation was studied;lastly,a method was developed to determine chlorfluazuron residue and on the basis of the optimized method,the stability of chlorfluazuron in methanol,test solution and matrices in the condition of different temperature as well as the comparision with two old-timey method were studied.The main results were summarized as follows:The determination condition of chlorfluazuron by HPLC with Hypersil ODS C18 reverse-phase column[250mm×4.6mm(i.d.),5μm].mobile phase:methanol/water(80/20,v/v),velocity of flow:1.0 ml/min,wavelength:254 nm,column temperature:25℃and injector volume:20μL.In the sample preparation,purification system was firstly optimized.When neutral alumina used as sorbent,petroleum ether/acetone (95/5,v/v) and petroleum ether /acetone (90/10,v/v) used as eluting solvent,recoveries all could achieve 94.7%.When florisil used as sorbent,petroleum ether/acetone (70/30,v/v) used as eluting solvent,recoveries also could achieve 94.7%.Because the price of florisil was much higher than neutral alumina,therefore the neutral alumina was selected as the sorbent;because the petroleum ether/acetone (90/10,v/v) did not favor further purification.Therefore the neutral alumina was selected as the absorbent,petroleum ether /acetone (95/5,v/v) was selected as the absorbent.When 0.01g of activated carbon was added to 4g of neutral alumina cloumn,the recovery could meet the requirements,but no purification effect was observed;when the amount of activated carbon increased to 0.1g, the recovery only achieved 14.2%,the majority of spiked chlorfluazuron was adsorbed by the 0.1g of activated carbon,recovery only rechieved 14.2%.When silver nitrate was added to 4g of neutral alumina cloumn,the recovery only achieved 27.0% and could not meet the demand of pesticide residue analysis.Therefore did not add other adsorbable substance to the neutral alumina packed column.When carried out the column purification,washed alumina column with 30mL of petroleum ether,discard eluates.Concentrated residue was introduced into the column with 5mL of petroleum ether /acetone (95/5,v/v),when the concentration residue solution liquid level fell to the upper surface of extreme anhydrous sodium sulfate,10mL of petroleum ether /acetone (95/5,v/v) was added to the column,abandoned former 15mL of eluate,finally used the 65mL of petroleum ether/acetone(95/5,v/v) to elute chlorfluazuron,collect for analysis.Acetone,acetonitrile were respectively used as extract solvent and partition into dichloromethane and petroleum ether,the recoveries all could reach as high as 93.0%.But acetonitrile is expensive and harmful to health,partition is troublesome when petroleum ether was used.Therefore,aetone was selected as extract solvent and partition into dichloromethane.As far as saving time,saving solvent,simplifying operation and enhancing working efficiency concerned,selected two times,100mL as the optimized results of the time and the amount of extraction and partition. When extraction time is 30min,40min and 50min,recoveries could achieve above 93%,also no remarkable difference. Finally,20 minutes was considered optimal for the extraction time because it gave the higher recovery and enhanced the working efficiency.When the sorbent was preserved to the 8th day,the recovery did not markedly reduce,therefore sorbent could preserve 8 days at least.The stability studies of chlorfluazuron indicated that,the degradation rate of the standard working solution preserved for 90 days in 4℃and -20℃were all under 4%, also chlorfluazuron in -20℃was stabler than chlorfluazuron in 4℃.Theoretically,the degradation rate should be higher after 50 days in 4℃,but lower in fact.The possible rearon is that the solvent has volatility,therefore, the standard working solution should preserve in -20℃.This could reduce degradation of chlorfluazuron and also could prevent the solvent from volatilization.With the increase of the storage number of days,recoveris of chlorfluazuron in four kind of matrix test solution and four kind of matrices all displayed reducing tendency gradually in 4℃and -20℃.In stability test of four kind of matrices test solution,except tomato test solution,degradation rates of other three kind of matrices test solution did not degrade faster in 4℃than in -20℃;But in four kind of matrices stability tests, degradation rates all displayed faster in 4℃compared with -20℃.The recovery experiment achieved satisfactory results . When the fortified concentration were 0.1-2.5mg/kg,the average recoveries of chlorfluazuron ranged between 85.8% and 100.6%,the RSD was 2.3-9.3%.This experiment also compared the optimized method with bypast methods.The results indicated that recoveries of the method were higher than the others,also saved the solvent,saved the time and the simplified operation,so this method have the superiority to other two methods.After a series of experiments,determination method of chlorfluazuron residue in the cabbage,Chinese cabbage,the tomato and capsicum was finally established.The method is of accurate identification and quantity,simple operation and economy.