Submitted to: Rapid Communications in Mass Spectrometry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2015
Publication Date: 5/15/2015
Citation: Nunez, A., Lehotay, S.J., Geis-Asteggiente, L. 2015. Structural characterization of product ions by electrospray ionization and quadrupole time-of-flight mass spectrometry to support regulatory analysis of veterinary drug residues in foods Part 2: Benzimidazoles nitromidaz...... Rapid Communications in Mass Spectrometry. 29(9):719-729.
Interpretive Summary: In the USA, the USDA Food Safety and Inspection Service (FSIS) is responsible for surveillance and enforcement monitoring of veterinary drug residues in meat and poultry products. Accordingly, methods for detection and quantification of regulated veterinary drug are of importance. A common method is the use of high-performance liquid chromatography coupled with mass spectrometry. In this approach, specific ions produced by the mass spectrometer are selected for analysis; however, the chemical structure of the chosen ions is seldom reported in the scientific literature. In this study, the chemical structure elucidation is reported for three ions each of 27 veterinary drugs of concern. This is part of the ongoing project in support of FSIS to complete 130 priority veterinary drugs for monitoring in the FSIS National Residue Program. The use of state of the art technology has allowed the precise determination of molecular formulas and chemical structures, which helps to avoid false positive results in regulatory applications not just in the US, but in worldwide programs related to food trade.
Technical Abstract: RATIONALE: Analysis for identification and quantification of regulated veterinary drug residues in foods are usually achieved by liquid chromatography coupled to tandem mass spectrometry. The instrument method requires the selection of characteristic ions, but structure elucidation is seldom performed to help ensure accuracy. This study is a continuation of previous work to characterize selected product ions in support of regulatory monitoring programs. METHOD: The tandem mass spectra of 27 veterinary drugs from a previously published LC-MS/MS method were analyzed with a high-resolution quadrupole time-of-flight mass spectrometer (Q-TOF) using electrospray ionization (ESI) in positive mode. The TOF analyzer was calibrated to achieve a mass accuracy error less than 5 ppm for the MS and MS/MS mode, and samples were infused for data acquisition. RESULTS: The high mass accuracy achieved in Q-TOF allowed elucidation of the molecular formulae of the product ions previously selected for qualitative identification. Rational interpretation of results was made and compared to the published literature, and the structure for the MS/MS fragments of four classes of regulated drugs (mectins, benzimidazoles, nitroimidazoles, and phenothiazines), totaling 27 compounds, were examined leading to report of new structures or confirmation of published structures using low resolution MS. CONCLUSIONS: Structural characterization of the product ions selected for identification and quantification of veterinary drug residues is important information for regulatory monitoring programs in defense of regulatory enforcement actions. This study has allowed structure elucidation of 81 MS/MS product ions previously selected for LC-MS/MS analysis of 27 drug analytes.