| Sample preparation is a critical step in the overall scheme of an analysis. Traditional methods for the sample preparations, including liquid-liquid extraction (LLE), solvent extraction, distillation and absorption, are time-consuming, tedious, and difficult for automation to some extent. Furthermore, large amounts of high purity organic solvents, which are potentially toxic and expensive, are usually consumed. Therefore, a lot of research efforts in separation science and related fields have been focused on the development of new sample preparation techniques, which are less time-consuming, more effective, simple, fast and require smaller amounts of organic solvents.The recent developments of the determination methods for pesticide residues and sample pre-treatment technologies were breifly summarized in the first part.In the thesis, several analytical methods were developed for the determination of some pesticides in agricultural and environmental samples by liquid–liquid microextraction and carbon nanotube reinforced hollow fiber microporous membrane solid phase microextraction (LLE-HF-MMSPE), solidification of floating organic drop liquid phase microextraction (SFO-LLME) and dispersive liquid–liquid microextraction method based on solidification of floating organic drop coupled with gas chromatography (GC).(1) simultaneous liquid–liquid microextraction and carbon nanotube reinforced hollow fiber microporous membrane solid phase microextraction (HF-MMSPE) coupled with gas chromatography (GC) was developed for the determination of amide herbicides (Alachlor, Acetochlor, Metolachlor, Pretilachlo, Butachlor) in water samples. The parameters that affect the extraction efficiencies, such as the type and concentration of carbon nanotube (CNTs), type of membrane solvent and desorption solvent, the type and volume of the extraction solvent in sample solution, extraction time and temperature, stirring rate, and ionic strength were investigated and optimized. Under the optimum conditions, the method showed a good linearity within a range of 0.2~600μg/L with the correlation coefficients (r) varying from 0.9978 to 0.9989. The limits of detection (LODs) were in the range of 0.06~0.2μg/L, the relative standard deviations (RSD) below 7.3%. The recoveries of the target analytes from water samples at spiking levels of 20.0 and 300.0μg/L were ranged from 85.9% to 114.0%. The results demonstrated that the developed method was an efficient pretreatment and enrichment procedure for the determination of amide herbicides in real water.(2) A simple and efficient liquid phase microextraction based on solidification of floating organic drop coupled with gas chromatography-flame photometric detection was developed for the extraction and determination of some triazine herbicides (metribuzin, simetryn, ametryn and prometryn) in soil samples. The type and volume of the extraction solvent, sample solution temperature, salt addition, stirring rate, and the extraction time for the extraction were optimized. Under the optimal conditions, the linear response was observed over the range of 10~2000 mg/kg for metribuzin and 2~500 mg/kg for simetryn, ametryn, and prometryn, respectively, with the correlation coefficients (r) varying from 0.9990 to 0.9992. The limits of detection were in the range between 0.2 and 1.0 mg/kg 20 (S/N=3). The recoveries of the target analytes for the spiked soil samples were ranged from 75.5% to 97.3%, with the relative standard deviation values less than 7.2% (n=5). The enrichment factors were achieved ranging from 122 to 336. The developed method was applied for the preconcentration and determination of the triazine herbicides in real soil samples and a satisfactory result was obtained.(3)A simple dispersive liquid–liquid microextraction based on the solidification of floating organic drop (DLLME-SFO) method coupled with gas chromatography–flame photometric detection (FPD) was developed for the determination of eleven kinds of organophosphorus pesticides in cucumber and green pepper. Compared with dispersive liquid-liquid microextraction (DLLME), DLLME-SFO is simple, precise and reproducible. Moreover, it uses less-toxic extractant solvent with melting point near room temperature, which makes it could be collected easily by solidification in the lower temperature. Some important factors that affect the extraction efficiencies, such as type and volume of the extraction solvent, temperature, salt effect, stirring rate and the extraction time were investigated and optimized. A good linearity (r≥0.9969) and a broad linear range 3~3000μg/kg for cucumber and 1~2000μg/kg for green pepper were obtained. The detection limits were in the range of 1~3.0μg/kg for cucumbe and 0.3~2.0μg/kg for green pepper. The recoveries of the target analytes from cucumber and green pepper samples were ranged from 81.1% to 107.8%. Good enrichment factors were achieved ranging from 135 to 383. The developed method was successfully applied for the preconcentration and determination of the organophosphorus pesticides in cucumber and green pepper, and satisfactory results were obtained. |
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