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Rationale: The retrospectivity (the ability to retrospect to a previously unknown compound in raw data) is very meaningful for food safety and risk assessment when facing new emerging drugs. Accurate mass and retention time based screening may lead to false positive and false negative results so a new retrospective, reliable platform is desirable. Methods: Different concentration levels of standards with and without matrix were analyzed using ion mobility (IM)‐quadrupole‐time‐of‐flight (QTOF) mass spectrometry to collect retrospective accurate mass, retention time, drift time and tandem mass spectrometry (MS/MS) evidence for identification in a single experiment. The isomer separation ability of IM and the four‐dimensional (4D) feature abundance quantification abilities were evaluated for veterinary drugs for the first time. Results: The sensitivity of the IM‐QTOF workflow was obviously higher than that of the traditional database searching algorithm [find by formula (FbF) function] for QTOF. In addition, the IM‐QTOF workflow contained most of the results from FbF and removed the false positive results. Some isomers were separated by IM and the 4D feature abundance quantitation removed interferences with similar accurate masses and showed good linearity. Conclusions: A new retrospective, multi‐evidence platform was built for veterinary drug screening in a single experiment. The sensitivity was significantly improved and the data can be used for quantification. The platform showed its potential to be used for food safety and risk assessment. [ABSTRACT FROM AUTHOR]

RATIONALE: Previously, we have reported a liquid chromatography/tandem mass spectrometry method for the identification and quantification of regulated veterinary drugs in food animals. The method uses three selected transition ions per analyte but structural characterization is also needed. This work is a continuation of two previous publications in which we propose structures of the selected transition ions of 130 veterinary drugs altogether. METHODS: In this work, 24 additional veterinary drugs were analyzed by infusion into a high-resolution quadrupole time-of-flight (QTOF) mass spectrometer using electrospray ionization (ESI) in positive or negative mode. The TOF analyzer was calibrated to achieve low error mass accuracy in the MS and MS/MS modes. Also, the MS² and MS³ spectra were obtained by using a Q-Trap mass spectrometer to further determine the possible pathways 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 including a review of the published literature led to the proposed structures of the MS/MS product ions of 24 compounds covering two classes of regulated veterinary drugs (anthelmintics and thyreostats). 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 helpful information for regulatory monitoring programs in defense of regulatory enforcement actions. Published in 2016. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]