Novel ultrasound-assisted mixed anionic-cationic surfactant-enhanced emulsification microextraction combined with HPLC for the determination of carbamate pesticides

A new approach based on ultrasound-assisted surfactant-enhanced emulsification microextraction using mixed anionic-cationic surfactants as emulsifiers was developed for the preconcentration of carbamate pesticides prior to HPLC analysis. Binary mixtures of anionic-cationic surfactants formed by different cationic surfactants and anionic sodium dodecyl sulfate were examined. A mixture of SDS and cetyltrimethyl ammonium bromide could enhance the extraction efficiency of carbamates. Chlorobenzene and chloroform were used as a dual extraction solvent. Other experimental parameters affected the extraction efficiency, including the composition of emulsifier and extraction solvent, effects of salt addition, ultrasonic extraction time and centrifugation time, were also optimized. Under optimum conditions, enrichment factors of between 100 and 200 fold were obtained, leading to lower limits of detection in the range of 0.1-5.0 mu g L-1, depending on the analytes. The calibration range of the method was linear over the wide range of 2-5000 mu g L-1, with correlation coefficients of 0.9844-0.9936. This newly established procedure was successfully applied in the analysis of carbamate residues in water and fruit juice samples. The recoveries of real samples at spiked levels of 250, 500 and 1000 mu g L-1 carbamates ranged from 81 to 112%.