Ultrasound-assisted surfactant-enhanced emulsification microextraction for the determination of carbamate pesticides in water samples by high performance liquid chromatography.

A novel ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME) coupled with high performance liquid chromatography-diode array detection has been developed for the extraction and determination of six carbamate pesticides (metolcarb, carbofuran, carbaryl, pirimicarb, isoprocarb and diethofencarb) in water samples. In the UASEME technique, Tween 20 was used as emulsifier, and chlorobenzene and chloroform were used as dual extraction solvent without using any organic dispersive solvent that is normally required in the previously described common dispersive liquid-liquid microextraction method. Parameters that affect the extraction efficiency, such as the kind and volume of the extraction solvent, the type and concentration of the surfactant, ultrasound emulsification time and salt addition, were investigated and optimized for the method. Under the optimum conditions, the enrichment factors were in the range between 170 and 246. The limits of detection of the method were 0.1-0.3 ng mL(-1) and the limits of quantification were between 0.3 and 0.9 ng mL(-1), depending on the compounds. The linearity of the method was obtained in the range of 0.3-200 ng mL(-1) for metolcarb, carbaryl, pirimicarb, and diethofencarb, 0.6-200 ng mL(-1) for carbofuran, and 0.9-200 ng mL(-1) for isoprocarb, with the correlation coefficients (r) ranging from 0.9982 to 0.9998. The relative standard deviations varied from 3.2 to 4.8% (n=5). The recoveries of the method for the six carbamates from water samples at spiking levels of 1.0, 10.0, 50.0 and 100.0 ng mL(-1) were ranged from 81.0 to 97.5%. The proposed UASEME technique has demonstrated to be simple, practical and environmentally friendly for the determination of carbamates residues in river, reservoir and well water samples.

Wu Q ，Chang Q ，Wu C ，Rao H ，Zeng X ，Wang C ，Wang Z ... -  《-》

Application of ultrasound-assisted surfactant-enhanced emulsification microextraction for the determination of some organophosphorus pesticides in water samples.

An ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME) was developed as a new approach for the extraction of organophosphorus pesticides (OPs) in water samples prior to high-performance liquid chromatography with diode array detection (HPLC-DAD). The use of a surfactant as an emulsifier in the UASEME method could enhance the dispersion of water-immiscible extraction solvent into aqueous phase and is favorable for the mass-transfer of the analytes from aqueous phase to the organic phase. Several variables that affect the extraction efficiency, including the kind and volume of the extraction solvent, the type and concentration of the surfactant, salt addition, ultrasound emulsification time and temperature, were investigated and optimized. Under the optimum experimental conditions, the calibration curve was linear in the concentration range from 1 to 200 ng mL(-1) for the seven OPs (isocarbophos, phosmet, parathion, parathion-methyl, fenitrothion, fonofos and phoxim), with the correlation coefficients (r) varying from 0.9973 to 0.9998. High enrichment factors were achieved ranging from 210 to 242. The established UASEME-HPLC-DAD method has been successfully applied for the determination of the OPs in real water samples. The limits of detection were in the range between 0.1 and 0.3 ng mL(-1). The recoveries of the target analytes over the three spiked concentration levels of the compounds (10, 50, and 100 ng mL(-1), respectively) in rain, reservoir and well water samples were between 83% and 106% with the relative standard deviations varying from 3.3% to 5.6%.

Wu C ，Liu N ，Wu Q ，Wang C ，Wang Z ... -  《-》

Application of dispersive liquid-liquid microextraction combined with high-performance liquid chromatography to the determination of carbamate pesticides in water samples.

Wu Q ，Zhou X ，Li Y ，Zang X ，Wang C ，Wang Z ... -  《-》

Dispersive liquid-liquid microextraction coupled with high-performance liquid chromatography-diode array detection for the determination of N-methyl carbamate pesticides in vegetables.

This paper described a simple, rapid and efficient method for the determination of N-methyl carbamate pesticides in tomato, cucumber, carrot and lettuce samples by dispersive liquid-liquid microextraction coupled with HPLC-diode array detection. Some experimental parameters that influenced the extraction efficiency, such as types and volumes of extraction and disperser solvents, extraction time and salt effect were examined and optimized. Under optimum conditions, the LOD of the method were 0.5-3.0 μg/kg depending on the compounds and the kind of vegetables. The linearities of the method were obtained in the range of 10.0-300 μg/kg for aldicarb, MTMC, carbofuran and carbaryl, and 20.0-600 μg/kg for isoprocarb, with the correlation coefficients ranging from 0.9921 to 0.9993. The RSD varied from 2.9 to 7.5% (n=5). The recoveries of the method for the five carbamates from vegetable samples at two different spiking levels were ranged from 77.8 to 98.2%. Results showed that the method we proposed can meet the requirements for the determination of N-methyl carbamate in vegetable samples and was finally applied to the analysis of target pesticides in vegetable samples taken from local markets.

Lin X ，Chen X ，Huo X ，Yu Z ，Bi K ，Li Q ... -  《-》

Preparation of a graphene-based magnetic nanocomposite for the extraction of carbamate pesticides from environmental water samples.

A graphene-based magnetic nanocomposite was synthesized and used for the first time as an effective adsorbent for the preconcentration of the five carbamate pesticides (metolcarb, carbofuran, pirimicarb, isoprocarb and diethofencarb) in environmental water samples prior to high performance liquid chromatography-diode array detection. The properties of the magnetic nanocomposite were characterized by scanning electron microscopy and X-ray diffraction. This novel graphene-based magnetic nanocomposite showed great adsorptive ability towards the analytes. The method, which takes the advantages of both nanoparticle adsorption and magnetic phase separation from the sample solution, could avoid some of the time-consuming experimental procedures related to the traditional solid phase extraction. Various experimental parameters that could affect the extraction efficiencies have been investigated. Under the optimum conditions, the enrichment factors of the method for the analytes were in the range from 474 to 868. A linear response was achieved in the concentration range of 0.1-50 ng mL(-1). The limits of detection of the method at a signal to noise ratio of 3 for the pesticides were 0.02-0.04 ng mL(-1). Compared with the dispersive liquid-liquid microextraction and the ultrasound-assisted surfactant-enhanced emulsification microextraction, much higher enrichment factors and sensitivities were achieved with the developed method. The method has been successfully applied for the determination of the carbamate pesticides in environmental water samples.

Wu Q ，Zhao G ，Feng C ，Wang C ，Wang Z ... -  《-》