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A CZE method with UV-Vis detection has been established and validated for the determination of nine sulfonamides: sulfapyridine, sulfamethazine, sulfamerazine, sulfamether, sulfadiazine, sulfadimethoxine, sulfamethoxazole, sulfachlorpyridazine, and sulfamethizole. Optimum separation was obtained on a 64.5 cm x 75 microm bubble cell capillary using a buffer containing 45 mM sodium phosphate and 10% methanol at pH 7.3, with temperature and voltage of 27 degrees C and 25 kV, respectively. p-Aminobenzoic acid was used as an internal standard . Taking into account the lack of sensitivity of the UV-Vis detection, the application of an on-line preconcentration methodology, such as large-volume sample stacking with polarity switching has been proposed. This procedure combined with a solvent extraction/SPE method applied for off-line preconcentration and cleanup provides a significant improvement in the LODs, ranging from 2.59 to 22.95 mug/L for the studied compounds; the quantification of these residues being possible below the levels established by EU legislation in animal food products, such as meat. Satisfactory recoveries were also obtained in the analysis of these compounds in ground water.

This paper presents two methods based on CZE-MS detection and CZE-MS/MS detection developed for the multiresidue determination of ten sulfonamides (sulfapyridine, sulfadoxin, sulfamethazine, sulfadimethoxine, sulfameter, sulfamerazine, sulfachlorpyridazine, sulfadiazine, sulfamethoxazole, and sulfamethizole) and a potentiator, trimethoprim (TMP), whose contents are regulated by the EU Council Regulation no. 2377/90 in animal edible tissues. Experimental designs were employed to optimize the electrospray conditions. MS/MS experiments using an IT as analyzer operating in multiple reaction monitoring (MRM) mode were carried out to achieve the minimum number of points according to the 2002/657/EC European Decision for unambiguous identification. The proposed procedures have been compared in terms of the performance characteristics and trueness. The limits of detection and quantification were in all cases lower than the maximum residue limits legislated for these compounds and the recoveries were satisfactory, being possible the application for their monitoring in foodstuff of animal origin and in environmental samples, allowing the determination of sulfonamides and TMP residues in meat and in superficial water in the low microg/L range.

). Separations were performed in an uncoated fused-silica capillary (70 cm  75 mm id, 55 cm effective length), using 20 mM borate buffer with 30 mM SDS (pH 8.5) and 7% ACN. In order to increase sensitivity, an on-line preconcentration procedure was applied, based on sweeping, using the same separation buffer without SDS as solvent of the sample. The precision of the method was evaluated in terms of repeatability and intermediate precision and the results were acceptable in all cases (RSDo12%). With the on-line preconcentration LODs (obtained as 3  S/N) were as low as 0.11, 0.52, 0.04 and 0.10 mg/L for G 2 , G 1 , B 2 and B 1 , respectively. Recovery studies were developed with extracts of rice samples spiked with aflatoxins, being in the range between 93.0 and 105.4%. The method has also been applied to the determination of aflatoxins in rice samples, and the results compared with those obtained by a standard method, being in good agreement.

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