High-performance liquid chromatography (HPLC) and micellar electrokinetic capillary chromatography (MECC) methods for the determination of different pesticides mixtures have been developed. These mixtures include triazine, phenylurea, phenoxyalkyl acid, carbamate and organophosphorous pesticides that have been selected because their use in different combinations in commercial formulations. The best results have been obtained by using mobile phase gradients in HPLC and by working with n-alcohols as mobile phase modifiers in MECC. When the quality parameters of both methods have been compared, it was observed that they are not sensitive enough for environmental analysis. In this sense two different concentration methodologies, off-line solid extraction by using Carbopack columns and a special injection MECC method, have been studied to enhance sensitivity. Off-line solid extraction can be used for both HPLC and MECC methodologies and permits to detect low ppb levels of individual pesticides. Special injection methods applied to the MECC system provides a 200-fold sensitivity improvement for the ionic pesticides.

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