Study On Application Of Dispersive Liquid-liquid Microextraction In The Determination Of Pesticide Residues In Foods

The sample pretreatment is a critical procedure in the analysis of pesticide residues in foods.The conventional pretreatment methods have the disadvantages of complicated steps,consuming time,high cost or poor treatment performance.An ideal method should have the characteristics of low cost,high accuracy,high selectivity,high sensitivity and good repeatability.However,the conventional pretreatment is difficult to meet these requirements.Dispersive liquid-liquid microextraction,a novel sample pretreatment method,has attracted much attention during its development process.Based on the previous research findings,this thesis tries to focus on the analysis of common pesticide residues in foods using three new dispersive liquid-liquid micoextraction methods.The contents were listed as follows:1.A novel method for simultaneous determination of nine organochlorine pesticides in Stauntonia chinensis DC samples has been established by dispersive liquid-liquid microextraction based on solidation of floating organic droplet(DLLME-SFO)coupled with gas chromatography(GC).The samples were extracted with petroleum ether,cleaned up with concentrated sulfuric acid,concentrated by DLLME-SFO and analyzed on the gas chromatography/electron-capture detector(ECD).Pesticides residues were quantitated by external standard method.Under the optimized conditions,the results showed that the working curve of the method provided a good linearity in the range of 1.0~100.0 ?g/L with the correlation coefficient greater than 0.99 for each pesticide.The limit of detection(LOD)for the method was 0.01~0.07 ?g/kg.The spiked recovery experiments were conducted at three concentration levels(1.75,7.00,28.00 ?g/kg),in which the average recoveries ranged from 83.3% to 116.7% and the relative standard deviations(RSDs)were 1.5~14%.The proposed method is efficient and of high sensitivity,which has been successfully applied to the determination for nine organochlorine pesticides in Stauntonia chinensis DC samples.2.A new method for determination of seven kinds of organophosphorus pesticides in fruits has been established by air assisted-dispersive liquid-liquid microextraction(AALLME)coupled with gas chromatography.The samples were extracted with ethyl acetate,concentrated by AALLME and analyzed on the gas chromatography/flame photometric detector(FPD).External standard method was employed to quantitate the pesticides residues in fruits.Under the optimized conditions,the method provided a good linearity in the range of 40.0~4000.0 ?g/L and the correlation coefficient is greater than 0.99 for each pesticide.The LOD for this method was 0.24~1.32 ?g/kg.Three concentration levels(12.0?300.0?1000.0 ?g/kg)were adopted on the spiked recovery experiments,the results showed the rate of recovery was 82.0~114.8% and the RSDs were 1.8~15.2%.The proposed method was found sensitive and accurate for the determination of seven kinds of organophosphorus pesticides in fruits.3.A simple and rapid microextraction technique,namely air-agitated liquid-liquid microextraction based on solidation of floating organic droplet(AALLME-SFO)was developed for the extraction of four pyrethroid pesticides in fruit juice.In this technique,much less volume of a low-density organic solvent was used as extraction solvent in the absence of disperser solvent.The enriched analytes were determined by ECD and quantified by external standard method.Under the optimized experimental conditions,the method provided a low LOD(0.01~0.03 ?g/L)and a good linearity in the range of 5.0~500.0 ?g/L with the correlation coefficient greater than 0.99 for four kinds of pyrethroids.The average spiked recoveries were 82.6~113.6% at three concentration levels(5?100?400 ?g/L)and RSDs were 1.4~14.1%.The proposed method has a superior performance on the determination of four pyrethroid pesticides in juice.To sum up,three novel dispersive liquid-liquid microextraction techniques were developed with the help of ultrasound and air assistance,which not only explore the application of DLLME in solid matrix,but also improve the analytical performance significantly.