Comparison of immunoassay and LC-tandem mass spectrometry analyses of ractopamine in hog oral fluid

Abstract

The accurate detection of ractopamine in food animals is crucial for marketing since some entities require animals or animal carcasses to be free of ractopamine residues. Field-based ractopamine screening tests that are rapid, sensitive, and capable of high-throughput are highly desirable to ensure that inadvertent exposure to ractopamine did not occur in animals marketed as animals that have not been fed ractopamine. An immunochemically based lateral flow assay was used to analyze oral fluids from hogs never exposed to ractopamine and from hogs that were presumed positives and results were confirmed using an enhanced sensitivity LC-MSMS method. We found that an immunochemically based lateral flow system having a working range of 2.5 to 15 ng mL⁻¹ worked well as a screening assay with 1.7% false positive results in freshly collected hog oral fluids. Using ractopamine glucuronide standards and LC-MSMS, we determined that the false positive results were not due to the presence of ractopamine glucuronide metabolites in oral fluids.

Keywords:

• Analytical method
• screening
• ractopamine
• ractopamine glucuronide
• oral fluid

Acknowledgements

We want to thank Robert Elder at Seaboard Foods for providing the previously screened hog oral fluid containing incurred residues. The authors wish to thank Ryan Sullivan and Robert Salter from Charm Sciences for helpful discussions. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer. This study was supported by USDA ARS Project no. 3060-32420-003-000-D.

Disclosure statement

No potential conflict of interest was reported by the authors.