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

Authors: Shelver, Weilin; McGarvey, Amy; Holthusen, Jason; YOUNG, JENNIFER - North Dakota State University; BYRD, CHRISTOPHER - North Dakota State University; Smith, David

Submitted to: Food Additives & Contaminants. Part A: Chemistry, Analysis, Control, Exposure & Risk Assessment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2023
Publication Date: 1/8/2024
Citation: Shelver, W.L., Mcgarvey, A.M., Holthusen, J.E., Young, J.M., Byrd, C.J., Smith, D.J. 2024. Comparison of immunoassay and LC-tandem mass spectrometry analyses of ractopamine in hog oral fluid. Food additives & contaminants. Part A: Chemistry, analysis, control, exposure & risk assessment. 41:162-174. https://doi.org/10.1080/19440049.2023.2300738.
DOI: https://doi.org/10.1080/19440049.2023.2300738

Interpretive Summary: Ractopamine is a feed additive used to promote animal growth which is approved for use in hogs, cattle, and turkeys in the US and several other countries. Many US trade partners, animal sports organizations, and some animal shows, however, prohibit ractopamine use and require that animals or animal carcasses be ractopamine-free. Animals that contain ractopamine residues may be disqualified from import/export and/or competition. Therefore, rapid screening assays that detect ractopamine in live animals have been widely adopted, especially by pork producers who export to countries where ractopamine is banned. The performance of a rapid (8 minutes) lateral flow test for detecting ractopamine in hog oral fluids (saliva) was compared with results obtained after mass spectrometric measurements of the same samples. The lateral flow test was useful for detecting ractopamine in oral fluids, but it performed better with freshly collected oral fluid samples compared to samples stored frozen for a prolonged time.

Technical Abstract: Accurate detection of ractopamine in food animals is crucial for marketing since some entities require animals or animal carcasses to be ractopamine-free. 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 ‘ractopamine-free’. We used an immunochemically based lateral flow assay to analyze oral fluids from hogs never exposed to ractopamine and from hogs that were presumed positives and confirmed the results 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 MS-MS/MS, we determined that the false positive results were not due to the presence of ractopamine glucuronide metabolites in oral fluids.