Micro-extraction, pre-concentration, and microfluidic-based separation of organophosphate insecticides followed by the miniaturized electrochemical detection system

Abstract

Introduction: A new analytical method based on the coupling of microextraction and microfluidics was developed and investigated for the pre-concentration, separation, and electrochemical detection of fenitrothion (FT) and parathion (PA) at the sub-ppm concentrations. Method: In the first step, the microchip capillary electrophoresis technique was used to serve as a separation and detection system. Analytes were injected into the 40 mm long microchannel with 10 mm sidearms. Then, they were separated by applying a direct electrical field (+1800V) between buffer and detection reservoirs. 2-(n-morpholino)ethanesulfonic acid (MES) buffer (20 mM, pH 5) was used as the running buffer. The electrochemical detection was performed using three Pt microelectrodes with the width of working, counter, and reference electrodes (50, 250, and 250 µm, respectively) in the out channel approach. Results: The system was devised to have the optimum detection potential equal to -1.2 V vs. Pseudo Ref. electrode. The dimensions of the SU-8 channel have 20 µm depth and 50 µm width. In the second step, an air-assisted liquid-liquid microextraction technique was used for the extraction and preconcentration of analytes from human blood plasma. Then, 1, 2 di-bromoethan was used as extractant solvent, the analytes were preconcentrated, and the sedimented solvent (50 µL) was evaporated in a 60 ˚C water bath followed by substitution of running buffer containing 10% ethanol. The optimum extraction cycles were found 8 with adding 1% NaCl to the aqueous phase. Analyzing time of the mentioned analytes was less than 100s, and the precision range was 3.3 – 8.2 with the linear range of 0.8 – 100 ppm and 1.2 - 100 ppm for FT and PA, respectively. The extraction recoveries were about 91% and 87% for FT and PA, respectively. The detection limits for FT and PA were 240 and 360 ppb, respectively. Finally, the reliability of the method was investigated by GC-FID. Conclusion: The proposed method and device were validated and can be used as in situ and portable detection system for detecting fenitrothion and parathion insecticides.