Desarrollo de un método de cromatografía capilar electrocinética micelar para la determinación de 5-nitroimidazoles en aguas de río

Abstract

5-nitroimidazoles (5-NDZs) represent a group of antibiotics with antiprotozoal and antibacterial properties. Some of them, as metronidazole, tinidazole and ornidazole, are used in human medicine, although they have had veterinary applications too. Since 90’s, the use of 5-NDZs in food-producing animals is forbidden by the European Union because these compounds and their metabolites possess genotoxic, carcinogenic and mutagenic properties. In this sense, Commission Regulation N. 37/2010 establishes that no residue of any 5-NDZs can be found in animals products intended for human consumption. However, they are still used as veterinary antibiotics according to the food alerts published in the Rapid Alert System for Food and Feed (RASFF) portal. Besides, 5-NDZs and their metabolites are very soluble in water and their biodegradability is low, so their presence in fish-farm water and meat industry effluents can produce their bioaccumulation. Considering that the capacity of current water treatment systems to remove antibiotics is low, 5-NDZs can be an environmental problem too. In this work we propose Micellar Electrokinetic Chromatography (MEKC) for the simultaneous determination of residues of 5-NDZs and their degradation products: metronidazole, metronidazole-OH, dimetridazole, dimetridazole-OH, ipronidazole, ipronidazol-OH, ternidazole, secnidazole, ronidazole and ornidazole. The separation takes place in around 20 min. The optimum conditions for an effective separation have been established: phosphate 20 mM, pH 6.5 with sodium dodecyl sulphate (SDS) 150 mM as electrophoretic buffer; applying a voltage of 25 kV at 20ºC. The sample, dissolved in phosphate buffer 20 mM pH 6.5, is introduced by hydrodynamic injection (50 mbar, 15 s) The compounds were monitored at 320 nm. An extended light path fused-silica capillary (64.5 cm × 50 μm I.D., 56 cm effective length) was used. Due to the lack of sensitivity inherent to capillary electrophoresis with UV–detection, a simple solid-phase extraction (SPE) method has been applied for off-line preconcentration and cleanup of water samples using Oasis HLB cartridges, achieving a preconcentration factor of 50. The performance characteristics of the method have been established, obtaining detection limits in the low ng/mL, which makes this method very useful for monitoring of these residues in different water samples, with recoveries over 90%, and satisfactory precision.