Submitted to: Rapid Communications in Mass Spectrometry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/7/2002
Publication Date: 5/28/2002
Citation: Churchwell, M.I., Holder, C.L., Little, D., Preece, S., Smith, D.J., Doerge, D.R. 2002. Liquid chromatography/electrospray tandem mass spectrometric analysis of incurred ractopamine residues in livestock. Rapid Communications in Mass Spectrometry 16:1261-1265. Interpretive Summary: Ractopamine HCl is feed additive recently approved by the US FDA to increase carcass leanness in finishing swine. Ractopamine use has not been approved in cattle, sheep, or other food animals in the United States, nor has it been approved for use in any food animals in Europe. Therefore a sensitive assay was needed that would provide unambiguous evidence of exposure to ractopamine in non-target animals. A liquid chromatographic method was developed utilizing electrospray mass spectrometry as the detector that detected ractopamine in a specific and highly sensitive manner in livers of cattle, sheep, turkeys, and ducks. The method was capable of detecting residues in livers and ocular tissues of cattle and sheep as long as seven days after the last exposure to ractopamine. Data derived from this study demonstrate that animal exposure to ractopamine remains detectable as long as seven days after the last exposure. The analytical method will be applicable for regulatory residue surveillance programs.
Technical Abstract: Ractopamine HCl is a beta-adrenergic agonist recently approved by the U.S. Food and Drug Administration for use in finishing swine, but is not approved by European regulatory agencies. The objective of this study was to develop and validate mass spectrometric methods for the detection and confirmation of ractopamine residues in livestock marker tissues. Incurred tissues in cattle, sheep, turkeys, and ducks were generated during 7-day ractopamine feeding (20 ppm in diets) periods. Ractopamine residues in liver and pigmented retinal epithelium were determined in animals slaughtered with withdrawal periods of 0, 3, and 7 days. Ractopamine was measured using LC and electrospray with MS/MS detection in the MRM mode. Total ractopamine residues (parent ractopamine + hydrolyzed conjugates) in liver were detected from all species on withdrawal day 0 (2-97 ppb) and were greatly diminished in all species by withdrawal day 7 (<1 ppb). Bovine and ovine retina, a potential reservoir for beta-agonists, had lower levels of ractopamine (0.5-3 ppb) than liver; ocular residues increased with withdrawal time, suggesting redistribution into this tissue. Incurred ractopamine residues were confirmed by the precise and accurate agreement of MRM intensity ratios of diagnostic fragment ions (m/z 284, 164, and 121) from the protonated molecule which were consistent with those produced by an authentic ractopamine standard. The limits of confirmation in liver and retina were below 1 ppb. These results demonstrate the utility of mass spectrometric methods in the measurement and confirmation of ractopamine residues for regulatory surveillance programs.