Extraction procedure for sulfachloropyridazine in porcine tissues and detection in a sulfonamide-specific enzyme-linked immunosorbent assay (ELISA) Original Research Article

Sulfonamide-specific polyclonal rabbit antibodies were obtained after immunization with a sulfathiazole derivative (N1-[4-(carboxymethyl)-2-thiazolyl]sulfanilamide = TS) coupled to keyhole lympet hemocyanin. Using these antibodies, two sulfonamide-specific enzyme-linked immunosorbent assays (ELISAs) were developed differing in coating antigen: TS-ovalbumin (TS-ova) and PS-ovalbumin (PS-ova, PS = N1-[4-methyl-5-[2-4-carboxyethyl-1-hydroxyphenyl]-azo-2-pyridyl]sulfanilamide). The detection of sulfamethazine, sulfamerazine, sulfadimethoxine, sulfadiazine, sulfathiazole, sulfapyridine, sulfachloropyridazine and sulfisoxazole in buffer was studied. Higher antibody titers were obtained in the ELISA coated with TS-ova (TS-ciELISA) as compared to the ELISA coated with PS-ova (PS-ciELISA), but the detection of sulfonamides was more sensitive in the PS-ciELISA, allowing the detection of all tested sulfonamides at the maximum residue level (MRL) value (100 ng ml−1). In a subsequent step, an extraction procedure was developed for the detection of sulfonamides in muscles, kidney, liver and fat by both ELISAs using sulfachloropyridazine as a model. As extraction buffer a carbonate/hydrogen carbonate buffer (pH 10) was chosen in which sulfonamides are highly soluble. Differences in homogenizing techniques (high-speed mixer (Ultraturax) versus vortex) and the effect of kaolin (hydrated aluminum silicate) treatment, to diminish the background signal in the ELISA, were evaluated. The best extraction procedure was the one using a vortex mixer as homogenizer and no kaolin treatment. Sulfachloropyridazine was easily detected at the MRL in all tissues.