Determination of 5-nitroimidazoles and metabolites in environmental samples by micellar electrokinetic chromatography

A method based on micellar electrokinetic chromatography (MEKC) with UV detection has been developed for the determination of nine 5-nitroimidazoles (5-NDZs), including metabolites in river water samples. Due to the relative insensitivity of UV detection in MEKC, a solid-phase extraction (SPE) method has been proposed that preconcentrates water samples fiftyfold and cleans them up off-line. An on-line preconcentration approach based on sweeping and the use of an extended light path fused-silica capillary (64.5 cm x 50 mu m i.d., 56 cm effective length) was also found to improve the sensitivity of the method. Separation was carried out in < 21 min using 20 mM phosphate buffer (pH 6.5) and 150 mM SDS as the background electrolyte (BGE). The temperature of the capillary was kept constant at 20A degrees C, a voltage of 25 kV was applied (normal mode), and a detected wavelength of 320 nm was utilized. Hydrodynamic injection (50 mbar for 15 s) of the samples, which were dissolved in 20 mM phosphate (pH 6.5), was employed. The limits of detection were lower than 1.1 mu g L-1. Recoveries of > 80% from spiked river water samples were obtained for most of the analytes at three different concentration levels with acceptable precision. This method could provide an efficient and economical alternative to the use of chromatographic methods to monitor nitroimidazole residues, thus supplementing the relatively few methods available for the analysis of these compounds in environmental samples.