Development of rapid immunoassays for the detection of ractopamine in swine urine

The monoclonal antibodies (mAbs) against ractopamine (Rac) were prepared and their properties identified by indirect competitive enzyme-linked immunoabsorbant assay (ELISA). The IC50 of mAbs was 2.7 ng ml−1 towards Rac or 9.3 ng ml−1 towards Rac-glucuronides and no cross-reactivity (CR) towards other competitors except dobutamine (CR: 3.76%). Based on the mAbs, the Rac-kit (kit) and Rac-strip (strip) were developed to detect Rac residues in swine urine. The strip and kit assay could be performed within 5–10 min and 2 h, respectively, allowing the analysis of urine samples without the need for sample clean-up. The detection limits were 1 ng ml−1 for kit and 3 ng ml−1 with the unaided eye, and 0.2 ng ml−1 with the Strip Reader for strip. The correlation coefficients (R 2) were 0.988 for kit in the range 0–128.0 ng ml−1, and 0.987 for strip in the range 0–10.8 ng ml−1. Comparing the gas chromatography-mass spectrometry (GC-MS) with the kit or strip in swine urine spiked with Rac standards, the differences ra...