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Immunoassays based on the current available antibodies for large multi-sulfonamide screening programs have suffered from high selectivity for individual sulfonamides and a wide range of selectivities for different sulfonamides. In this study, five synthesized haptens, HS, BS, CS, SA10, and TS and two sulfonamides, SG and SMX were used as haptens, which may or may not contain a ring structure at the N1 position of the sulfonamides, were selected to evaluate the effectiveness for producing group-specific monoclonal antibodies (MAbs). Mice immunized with three different two-ring haptens were used for hybridoma production, which resulted in three unique MAbs recognizing 10, 13, and 15 sulfonamides showing 50 % inhibition (IC) at concentrations below 100 ng mL. MAb 4D11 derived from one novel immunizing hapten could recognize 12 sulfonamides with IC values ranging from 1.2 to 12.4 ng mL, almost within 1 order of magnitude. These produced MAbs show lower IC values in addition to significantly improved group specificity compared with previously generated MAbs. This study clearly indicates that the careful selection of the immunizing hapten has an important effect on the specificity of the generated antibodies. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Methyl-3-quinoxaline-2-carboxylic acid (MQCA) is a possible residue marker for three quinoxaline veterinary medicines (olaquindox, mequindox, and quinocetone). The wide application of mequindox/quinocetone or the illegal use of olaquindox leads to MQCA residue in animal's original food, thereby threatening the safety of human food. The indirect competitive enzyme-linked immunosorbent assay (IC-ELISA) with a specific coating antigen and monoclonal antibody (MAB) was established and optimized for detecting MQCA in swine liver. Samples were acidified with 2 mol l hydrochloric acid, extracted with ethyl acetate-hexane-isopropanol (8 + 1 + 1, v/ v/ v) and then detected by IC-ELISA. The logarithm correlation of standards to OD values ranged from 0.2 to 200 μg l, with IC of 6.46 μg l. Negligible cross-reactivity happened to five quinoxaline antibiotics (olaquindox, mequindox, quinocetone, carbadox, and cyadox) and the metabolite of carbadox and cyadox (quinoxaline-2-carboxylic acid). When spiked with 1 to 100 μg kg of MQCA, the recoveries ranged from 85.44 to 100.02 %, with the intra-assay coefficient of variation (CV) of 6.64-10.57 % and inter-assay CV of 7.29-10.88 %. The limit of detection for MQCA was 1.0 μg kg in swine liver. Furthermore, incurred samples were detected by the IC-ELISA and then conformed by a reported LC/MS/MS method, it shown that there was good correlation between the two methods. All these results indicated that the IC-ELISA method is appropriate for surveillance MQCA residue in animal tissues. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]