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Title: ESI-Q-TOF structural characterization of prominent MS/MS product ions of veterinary drugs for improved regulatory monitoring

item Nunez, Alberto
item Lehotay, Steven
item GEIS-ASTEGGIENTE, LUCIA - University Of Maryland

Submitted to: Proceedings of the ASMS Conference on Mass Spectrometry and Allied Topics
Publication Type: Proceedings
Publication Acceptance Date: 6/6/2014
Publication Date: 5/31/2015
Citation: Nunez, A., Lehotay, S.J., Geis-Asteggiente, L. 2015. ESI-Q-TOF structural characterization of prominent MS/MS product ions of veterinary drugs for improved regulatory monitoring. Proceedings of the ASMS Conference on Mass Spectrometry and Allied Topics.

Interpretive Summary:

Technical Abstract: Introduction The misuse of veterinary drugs in animal production could result in a negative impact on food safety, drug resistance, and in the environment. Consequently, countries around the world have regulated their use, which requires effective methods for the qualitative and quantitative residue analysis. LC-MS/MS methods based on the selection of characteristic ions are very effective, but analysts nearly always simply choose the most intense ions without knowing the structures or mechanism of formation. The quadrupole analyzers used do not have the needed accuracy for structural identification. In this study, a Q-TOF instrument was calibrated to produce an error less than 5 ppm to characterize product ions of priority drugs. Methods A Waters Synapt G1 Q-TOF mass spectrometer operating in the W mode was used to measure the MS and corresponding MS/MS product ions. The instrument was calibrated using the exact mass of the ion products of [Glu-1]-fibrinopeptides. Samples dissolved in acetonitrile:water or methanol:water (50:50, 0.1 percent formic acid) were infused into the mass spectrometer for analysis. The MS/MS spectra of the selected analytes were obtained with collision energies adjusted to produces a precursor ion peak ([M+H]+ or the [M+Na]+) that allowed the calibration of the mass spectrum with error less than 5 ppm. For drugs with preference for the Na+ adduct, a solution of ammonium formate in methanol:water (50:50) was used to obtain the product ions from the [M+NH4]+ precursor adduct. Preliminary results The Food Safety and Inspection Service (FSIS) is the public health agency of the US Department of Agriculture (USDA) responsible for surveillance and enforcement monitoring of veterinary drug residues in meat and poultry products (among other food safety responsibilities). Previously, we transferred to FSIS a method utilizing UHPLC-MS/MS to rapidly screen, identify, and quantify more than 100 priority veterinary drugs in animal tissues. The method is based in the selection of 3 MS/MS ion products of each drug analyzed that must occur at the same, proper retention time and peak shapes as the reference standard to avoid false positives. An additional requirement is that the ion transitions chosen make sense structurally, and ideally, the fragments would be reasonably unique to the analyte. However, the low mass resolution of quadrupole MS/MS instruments makes it difficult to obtain adequate high mass accuracy to determine the molecular formula of the MS/MS ions and consequently their structures. The elucidation of the fragments corresponding to three groups of dugs, mectins (anthelmintics), phenothiazines (tranquilizers), and 5-nitroimidazoles (antibiotics and coccidiostats) were analyzed using a Q-TOF mass spectrometer. The proposed fragmentation patterns were based on molecular formulas obtained from ions with less than or equal to 5 ppm mass accuracy. The scientific and regulatory support goals of the study were met, and problems in the FSIS method with adduct ion formation of mectins were explained. Novel aspect Structural characterization of MS/MS product ions for improved identification of regulated veterinary drugs based on high accuracy Q-TOF mass spectrometry.