An enzyme-linked immunosorbent assay (ELISA) to screen sulfadiazine and sulfamethazine residues in feeds has been developed and validated according to Commission Decision 2002/657/EC criteria. Sulfonamides are easily extracted with a 95:5 acetonitrile/water mixture, obtaining recoveries between 80 and 100%. Accuracy, precision, selectivity, robustness, limit of detection (LOD), and detection capability (CCbeta) of the assay have been assessed during the validation process. LOD values in pig feed samples were 0.2 microg/g for sulfadiazine and 0.04 microg/g for sulfamethazine without any sample treatment other than extraction, dilution with the assay buffer, and filtering of the resulting solution. Furthermore, a new strategy for the determination of CCbeta in an ELISA screening method is proposed; this gave CCbeta values of 0.8 microg/g for sulfadiazine and 0.1 microg/g for sulfamethazine. Besides sulfadiazine and sulfamethazine, other sulfonamides can be detected with this immunoassay; this has been verified calculating their LOD values and cross-reactivities. Finally, real feed samples were analyzed with the ELISA methodology and a previously developed liquid chromatography (LC) method, and results confirmed the utility of this new immunoassay for screening purposes.
International audienceA feasibility study of the preparation of quality control materials for the analysis of medicated feeds has been carried out. Two analytical methodologies for the analysis of sulfonamides in feeds have been developed, validated and applied to the homogeneity and stability studies. Pig feeds spiked with sulfadiazine and sulfadimidine have been prepared. The drugs were spiked at 500 µg g-1, representing what can be expected in a commercial medicated feed, and at 2 and 5 µg g-1 which roughly correspond to drug-free feeds cross-contaminated during the fabrication process. The homogeneity of both the bulk and the bottled materials was verified. A stability study of the materials containing 2 and 5 µg g-1 of sulfonamides has been carried out over an eighteen-month period at room temperature, at 4˚C and at -20˚C. The determination of sulfadiazine and sulfadimidine in samples coming from these homogeneity and stability studies of the quality control materials was carried out by liquid chromatography with either UV or fluorimetric detection, depending on the concentration of the analytes in the samples
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