Application of Liquid Phase Microextraction Coupled with High Performance Liquid Chromatography in the Analysis of Some Pesticide and Veterinary Drug Residues

Abstract: In the thesis, on the basis of the hollow fiber-based liquid-phase microextraction ( HF-LPME ) and Dispersive liquid–liquid microextraction ( DLLME ) technique in combination with high performance liquid chromatography ( HPLC ), several analytical methods were developed for the determination of some pesticides and veterinary drugs in agricultural and environmental samples. This thesis is mainly concerned with the following aspects:( 1 ) A novel HF-LPME coupled with HPLC was developed for the determination of three macrolide antibiotics in milk. Some important extraction parameters, such as the effect of the pH of the sample solution, extraction time, stirring rate and ion strength were optimized. The new method provided a good average enrichment factor of 34, 52 and 47 for tilmicosin, midecamycin and josamycin, respectively. A good linear relationship existed in the range of 0.05 ~ 5μg/mL of each compound in milk with the correlation coefficients ( r ) of 0.9978, 0.9986 and 0.9989, and the detection limits of 5, 2 and 2 ng/mL ( S/N = 3:1 ) for tilmicosin, midecamycin and josamycin, respectively. The recoveries were between 79.0% and 105.3% with the relative standard deviations ( RSDs ) ranging from 5.3% to 9.4%. The method was shown to be simple, efficient and sensitive, and was suitable for the determination of these compounds in milk.( 2 ) A novel HF-LPME coupled with HPLC was developed for the determination of clenbuterol in pork. Some important extraction parameters, such as the effect of the pH of the sample solution, extraction time, stirring rate and salt concentration were optimized. On the basis of the experiments, the optimal HF-LPME conditions were selected as follows: the pH of sample solution ( donor phase ) at 11 and toluene as extraction solvent. The extractions were conducted for 20 min at a stirring rate of 1000 rpm. After extraction, the extraction solvent was evaporated to dryness under a stream of nitrogen at room temperature. The residue was reconstituted in 15μL acetonitrile, and then a volume of 10μL was injected onto the HPLC system for analysis. The new method provided an enrichment factor of 78 for clenbuterol. The linear relationship existed in the range from 10 to 2000 ng/mL for the compound in pork with the correlation coefficient ( r ) of 0.9995, and the detection limit of 0.8 ng/mL ( S/N = 3:1 ). The recoveries at three concentration levels were 84.9%, 91.4% and 95%, with the RSDs ranging from 4.6% to 6.3%. The method was simple, sensitive, and was easy to use for the determination of clenbuterol in pork.( 3 ) A new HF-LPME method coupled with HPLC-fluorescence detection ( FD ) method was developed for the determination of carbendazim ( MBC ) and thiabendazole ( TBZ ) in apple juice. Some important extraction parameters, such as the pH of the sample solution, extraction time, stirring rate and salt concentration were optimized. As a result, the optimal HF-LPME conditions were selected as follows: the pH of sample solution (donor phase) was 7.5, the pores of the hollow fiber were impregnated by 1-octanol, and 5 mM HCl ( pH=2.5 ) was used as the extraction solvent. The extractions were conducted for 40 min at a stirring rate of 800 rpm. After extraction, 10μL of the extraction solvent was injected into the HPLC system for analysis. The average enrichment factors were 106 and 114 for MBC and TBZ, respectively. The linear relationship existed in the range of 2.5 ~ 500μg/L and 5 ~ 500μg/L for MBC and TBZ in apple juice with the correlation coefficients ( r ) of 0.9995 and 0.9991, respectively. The detection limits were 0. 8μg/L for MBC and 1.5μg/L for TBZ ( S/N = 3:1 ). The recoveries were between 86.3% and 106.0% with the RSDs ranging from 3.3% to 11.5%. The HF-LPME-HPLC method has been successfully applied to the analysis of MBC and TBZ in apple juice, indicating that LPME-HPLC may be a promising combination for the analysis of pesticide residues for some food matrix samples.( 4 ) A novel method for the determination of five carbamate pesticides ( metolcarb, carbofuran, carbaryl, isoprocard and diethofencard ) in water, watermelon and tomato samples was developed by DLLME coupled with HPLC-diode array detector ( HPLC-DAD ). Some experimental parameters that influence the extraction efficiency were studied and optimized to obtain the best extraction results. Under the optimum conditions, the calibration curve was linear in the concentration range from 5 to 1000 ng/mL for all the five carbamate pesticides, with the correlation coefficients ( r ) varying from 0.9982 to 0.9994. Good enrichment factors were achieved ranging from 80 to 177, depending on the compound. The limits of detection ( LODs ) ( S/N = 3 ) were ranged from 0.1 to 1.5 ng/mL. The method has been successfully applied to the analysis of the pesticide residues in environmental water, watermelon and tomato samples. The recoveries ranged from 76.2% to 97.2% with RSDs less than 8.7%, indicating the feasibility of the DLLME method for the determination of the five carbamate pesticides in water, watermelon and tomato samples…
Key words: Hollow fiber-based liquid phase microextraction; dispersive liquid-liquid microextraction; high performance liquid chromatography; pesticide residues; veterinary drug residues

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