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Submitted to: Journal of Rapid Communications in Mass Spectroscopy
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/10/2016 Publication Date: 2/29/2016 Citation: Nunez, A., Lehotay, S.J., Lightfield, A.R. 2016. Structural characterization of product ions of regulated veterinary drugs by electrospray ionization and quadrupole time-of-flight mass spectrometry (part 3) Anthelmintics, thyreostats, and flukicides. Journal of Rapid Communications in Mass Spectroscopy. 30:813-822. Interpretive Summary: Veterinary drugs are frequently used in animal production and the U.S. strictly regulates their applications and withdrawal times to ensure compliance with good veterinary practices and improved food safety. The USDA Food Safety and Inspection Service (FSIS) is responsible for surveillance and enforcement of monitoring of veterinary drug residues in meat and poultry products. One of the methods used by FSIS is based on the monitoring of drug residues by the use of selected ion fragments produced by mass spectrometry in association with high-pressure liquid chromatography. These ion are selected based their intensity for use in identification and quantification. However, it is important to understand the fragmentation path for the ion selected. The work in this study is the continuation of our effort to elucidate the structure of the selected ion fragments by using advance high resolution mass spectrometry instrumentation. Additional 24 veterinary drugs were examined and the ion formulas with the corresponding structure were elucidated with this technology. This works serves to reduce chances for false positives and negatives in the monitoring program, and provides justification and defense in regulatory enforcement actions. Technical Abstract: RATIONALE: Previously we have reported a liquid chromatography tandem mass spectrometry method for the identification and quantification of regulated veterinary drugs. The methods used three selected transition ions but most of these ions lacked structural characterization. The work presented here is a continuation of two previous publications and is proposing the structure of the selected transition ions of 24 additional veterinary drugs based on the spectra data from a Q-TOF instrument. METHOD: The MS/MS of 24 additional veterinary drugs from a previously published LC-MS/MS method were analyzed by infusion into a high-resolution quadrupole time-of-flight mass spectrometer (Q-TOF) using electrospray ionization (ESI) in positive or negative mode. The TOF analyzer was calibrated to achieve low error mass accuracy for the MS and MS/MS mode. Also, the MS2 and MS3 were obtained by using a Q-Trap mass spectrometer to further determine the possible pathway of ion formation. RESULTS: The low error mass spectrometry analysis allowed the elucidation of the ion formulae of selected transition ions for qualitative identification. The rational interpretation of data and published literature led to the proposed structure of the MS/MS product ions of 24 compounds covering three classes of regulated veterinary drugs (anthelmintics, thyreostats, and flukicides). In addition, the use of MS2 and MS3 experiments led to the establishment of fragmentation patterns. CONCLUSIONS: The identification and quantification of veterinary drug residues is essential information for regulatory monitoring programs in defense of regulatory enforcement actions. This study adds the structure elucidation of 72 MS/MS product ions previously selected for LC-MS/MS analysis of 130 drug analytes. |
