An ultrasound-assisted dispersive liquid-liquid microextraction method based on solidification of floating organic droplets (UA-DLLME-SFO) followed by gas chromatography-flame ionization detection (GC-FID) was developed for the extraction and determination of pesticides including buprofezin, triazophos, lambda-cyhalothrin, pyridaben, and es-fenvalerate in water samples. The influence of different parameters affecting the performance (the nature of extractant and disperser solvents as well as their volumes, salt addition, extraction and ultrasonication time) was evaluated in detail. Under the optimized conditions (extraction solvent: 8 mu L 1-dodecanol; dispersive solvent: 300 mu L acetonitrile; 1% (w/v) NaCl; ultrasonication time: 3 min), the obtained enrichment factors were between 143 and 813. The linear range was 0.20-200 mu g L-1 with correlation coefficients higher than 0.9976. Based on a signal-to-noise ratio of 3, limits of detection were in the range of 0.11 to 0.48 mu g L-1, depending on the compounds. Relative standard deviations (%) were less than 3.5% (n = 5) for both intra-and inter-day analyses. The proposed UA-DLLME-SFO-GC-FID method was successfully applied for the determination of pesticides in water samples with recoveries varying from 92.2 to 109.4%.

A simple and rapid efficient method was developed for the determination of phthalate esters using dispersive liquid–liquid microextraction followed by gas chromatography with flame ionization detection. A mixture of isopropanol (0.75 mL, dispersant) and carbon tetrachloride (30 µL, extractant) with sodium chloride (1%, w/v) was used for extraction. Under optimum conditions, the method provided linear calibration curves between 0.5 and 200 µg L−1 for dibutyl phthalate, and 1.0 and 200 µg L−1 for butyl benzyl phthalate, diethyl phthalate, and diisooctyl phthalate. The relative standard deviations for intra-day and inter-day analyses were less than 5.8% and 6.9%, respectively, with enrichment factors between 229 and 424. Two wine samples were analyzed with recoveries between 70.1% and 119.3%.

A simple and sensitive method for detecting diprophylline (DPP) was developed based on the fluorescence quenching of glutathione-capped CdTe quantum dots (GSH–CdTe QDs) by using diprophylline in a KH2PO4–Na2HPO4 medium. Parameters affecting the quenching efficiency, including types and pH of buffer solutions as well as temperature, reaction time, adding sequence, and interfering substances, were investigated and optimized. In optimum conditions, the calibration plot of the quenched fluorescence intensity F0/F with a DPP concentration range of 1.67×10–6molL−1 to 1.33×10–5molL−1 was linear. The detection limit (with signal to noise ratio of 3) for DPP was 2.24×10–7molL−1. The proposed method was successfully applied for detecting DPP in human serum. The recovery of the method was in the range of 87.41% to 117.94%. Finally, the possible quenching mechanism of GSH–CdTe QDs and DPP was also discussed.

A review on the progress of application of dispersive liquid-liquid micro-extraction(DLLME)to gas chromatographic determination of residual amounts of pesticides was given in this paper,relating especially to the topics on the principle and procedure of extraction,the influential factors of extraction,including extraction solvent,dispersing agents,extraction time,values of pH and ionic strength(55ref.cited).

In this study, a simple and efficient method has been developed to analyze pesticides in water samples using ultrasonic-assisted dispersive liquid–liquid microextraction (UA-DLLME) combined with gas chromatography-flame ionization detection (GC-FID). Several parameters, including type and volume of extractant and dispersant, extraction time, and amount of salt on extraction performance, were optimized in detail. A mixture of acetonitrile (1.0 mL, dispersant) and carbon tetrachloride (15 μL, extractant) was used for extraction. Under optimal conditions, enrichment factors were obtained between 315 and 1153. The linearity of the method ranged from 1 to 100 μg L−1 with correlation coefficients ≥0.9990. Limits of detection (S/N = 3) ranged between 0.09 and 0.57 μg L−1, depending on the compounds. Relative standard deviations were <8.0 % (n = 5) for both intra- and inter-day analyses. The proposed method was successfully applied for the preconcentration and determination of pesticides in water samples (river water, tap water, and lake water) with recoveries that varied from 90.5 to 107.7 %.

An efficient and durable online capillary immobilized trypsin microreactor was successfully established to study the enzyme kinetics of trypsin and screen its inhibitors from natural extracts through capillary electrophoresis (CE). In this procedure, trypsin was immobilized on the inner wall at the inlet of the capillary treated with 3-aminopropyltrimethoxy silane (3-APTES), producing a trypsin microreactor via cross-linking of glutaraldehyde with 3-APTES and trypsin. The rest of the capillary was selected as a channel for separating the generated product and unreacted substrate of the trypsin enzymatic reaction. The parameters affecting the separation efficiency and activity of immobilized trypsin were evaluated systematically. The optimized conditions were as follows: 50mM Tris–HCl (pH 8.0), 15kV, 37°C, 10mM substrate, incubation for 2min. Under optimal conditions, separation of the product and substrate was achieved through CE within 3.5min. The obtained results of Michaelis constant, inhibition kinetics constant, and half-maximal inhibitory concentration for the immobilized trypsin using benzamidine hydrochloride hydrate as a model inhibitor were 1.56, 1.79 and 3.98mM, respectively. The proposed method was successfully applied for screening of trypsin inhibitors from 19 kinds of natural extracts.

Changes in biomarkers of a duck serum from stressed environments represent a reliable tool in evaluating toxious effect of cropland biogeocerose. A new and alternative enzymatic spectrophotometric indicator, 2,6-dimethylbenzoquinone (2,6-DMBQ) was explored to assess the organophosphate impact on cholinesterase (ChE) from duck serum. The enzymatic activity could be assessed by measuring the absorbance decrease at 257 nm wavelength and the decrease of enzymatic activity is related with the inhibiton of parathion methyl on cholinesterase.