Rapid Screening of Quinoxaline Antimicrobial Growth Promoters and Their Metabolites in Swine Liver by Indirect Competitive Enzyme-Linked Immunosorbent Assay

Quinoxaline feed additives are antimicrobial growth promoters (AGPs); use three of them is permitted, and two of them are illegally used. It results in residue of quinoxaline AGPs and their metabolites in edible animal tissues, which are potentially harmful to human health. In order to effectively monitor the multiple residues of them in swine liver, an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) was developed based on polyclone antibody preparation. Protein conjugates were synthesized and immune to New Zealand white rabbit according to designed schemes. The effective antiserum with 50 % inhibiting concentration (IC₅₀) value of 1.34 μg?L^?1 was obtained. A new synthesized quinoxaline with similar chemical structure to olaquindox but longer spacer arm was used as coating antigen. Cross-reactivity of other four quinoxaline AGPs and their eight metabolites was tested; seven of them have cross-reactivity over 10 %, with IC₅₀ of 0.10–2.50 μg?L^?1. At the spike level of 1 to 100 μg?kg^?1 in swine liver, the recoveries of all compounds ranged from 80.14 % to 96.90 %, with the inter-day variation coefficient (CV) of 5.67–13.82 % and the intra-assay CV of 6.22–14.19 %. The limit of detection ranged from 0.03?±?0.002 to 0.79?±?0.05 μg?L^?1. Positive samples were determined by the ic-ELISA method and successfully confirmed by liquid chromatography-tandem mass spectrometry. The proposed ELISA is feasible for screening quinoxaline AGPs and their metabolites in swine liver.