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

Abstract

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 ranged from 1.4% to 4.5% for kit and 1.0% to 4.7% for strip. However, the differences were greater than 54% for the kit and 55% for the strip test for the analysis of urine from swine treated with Rac. The results obtained from GC-MS using hydrolysed urine samples were generally in good agreement with those obtained from strip or kit using non-hydrolysed urine samples.

Keywords:

• immunoassays
• animal products
• veterinary drug residues
• ractopamine
• rapid
• detection

Acknowledgements

This study was supported by the National Technology Support Program of China (Grant Number 2006BAK02A21) and the National High Technology Research and Development Program of China (Grant Number 2001AA249031).