Application of a multi-sulfonamide biosensor immunoassay for the detection of sulfadiazine and sulfamethoxazole residues in broiler serum and its use as a predictor of the levels in edible tissue

A multi-sulfonamide biosensor immunoassay (BIA), based on a previously developed mutant antibody (A.3.5) in an optical biosensor (Biacore 3000), was applied to analyse the serum and plasma samples obtained from the broilers treated with sulfamethoxazole and sulfadiazine. The assay was fast (5 min per sample), the sample preparation easy (dilution in antibody containing buffer only) and an equal sensitivity for the two sulfonamides was obtained with limits of detection (LOD) in serum and plasma below 10 ng ml−1. The concentrations found with the BIA in serum and plasma of the treated broilers were comparable and higher than the concentrations found in the tissue by LC-MS/MS. The average serum/tissue ratios for sulfamethoxazole were 6.2 (leg meat), 2.5 (liver) and 1.3 (skin + fat) and for sulfadiazine 8.7 (leg meat), 3.1 (liver) and 2.2 (skin + fat). To predict the concentrations of the two sulfonamides below the maximum residue limit (MRL) of 100 ng g−1 in the tissue with the highest level (skin + fat), the proposed action level of the multi-sulfonamide BIA in serum is 130 ng ml−1. A later developed mutant antibody (M.3.4), with a better sensitivity towards more sulfonamides, was applied during a survey. Serum samples (n = 300) of broilers from 30 different flocks were found negative. Concentrations between <5 and 152 ng ml−1 (sulfamethoxazole equivalents) were found in the serum samples of one flock (n = 160) with an average of 25 ± 21 ng ml−1. The sulfonamide identified by LC-MS/MS in these samples was sulfamethoxazole.