Capillary electrochromatography coupled with dispersive liquid-liquid microextraction for the analysis of benzimidazole residues in water samples.

A novel method for the analysis of benzimidazole residues in water samples by capillary electrochromatography-UV detection (290nm), using laboratory-made packed columns is presented. Capillaries (25cm packed length×75µm inner diameter, 34cm total length, 25.5cm effective capillary length) were packed with C18 particles (5µm, non-encapped) following a high pressure packing procedure and using a compact steel unit designed for packing capillary columns. Acetone was employed as solvent to carry the particles through the capillary and pack it under a pressure of 42MPa. Outlet and inlet frits were made by sintering the particles of the stationary phase by heating the packed material with a nichrome ribbon connected to a 7V AC power supply. With the aim of achieving a good analytical performance, the variables that affected the separation were studied, using a mobile phase composition of 60:40 (v/v) acetonitrile/water containing ammonium acetate (1mM, pH 6.5), a separation voltage of 25kV and a temperature of 25°C. In addition, a combined hydrodynamic-electrokinetic injection mode was considered and samples were injected for 75s under a voltage of 12.5kV and a pressure of 11.5bar. Finally, the determination of benzimidazoles in water samples was accomplished by capillary electrochromatography using dispersive liquid-liquid microextraction as sample treatment. Variables affecting the extraction efficiency were optimized, using chloroform and ethanol as extraction and disperser solvents, respectively. This method was applied to different water samples, obtaining satisfactory results in terms of linearity (R2≥0.990), repeatability (RSD≤1.2%), reproducibility (RSD≤2.2%) and trueness (R≥87.7%). Detection and quantification limits were lower than 2.8µgL-1 and 9.3µgL-1, respectively.