Biosensor assay of sulfadiazine and sulfamethazine residues in pork

Biosensor-based immunochemical screening assays for the detection of sulfad iazine (SDZ) and sulfamethazine (SMT) in muscle extract from pigs were deve loped. Samples were extracted with aqueous buffer and then centrifuged. Thi s simple and straightforward preparation allowed up to 40 samples to be pro cessed and analysed in 1 d. The limits of detection for the assays were fou nd to be 5.6 ng g(-1) for SDZ and 7.4 ng g(-1) for SMT. These figures were well below the European and US legal limits for sulfonamides (100 ng g(-1)) . The precision (RSD) between runs was < 8% and the recovery was between 91 and 98%. The validation proved the assays to be accurate and the analysis of routine field samples showed good correlation with an established TLC sc reening procedure. No false negative or positive results were obtained with blank and spiked samples. The influence of cross-reacting metabolites on i mmunoassays was demonstrated by testing incurred tissue samples, collected from sulfonamide treated pigs after only a short withdrawal period. The qua ntitative results obtained by biosensor analysis were a combination of pare nt sulfonamide plus N-4-acetyl metabolite while the HPLC method used for co nfirmatory analysis detected only the parent sulfonamide. This gave rise to some false positive results and highlighted the need to use real samples i n evaluating any assay thoroughly. False negative results were not obtained .