title: Structural characterization of product ions of regulated veterinary drugs by electrospray ionization and quadrupole time-of-flight mass spectrometry. Part 3: Anthelmintics and thyreostats.
abstract: BACKGROUND
  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 MS(2) and MS(3) 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 MS(2) and MS(3) 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.
authors.affiliation: US Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA, 19038, USA.
authors.forename: Alberto
authors.initials: A
authors.lastname: Nuñez
authors.affiliation: US Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA, 19038, USA.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Lehotay
authors.affiliation: US Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA, 19038, USA.
authors.forename: Alan R
authors.initials: AR
authors.lastname: Lightfield
mesh_terms: D000871:Anthelmintics / Q000032:analysis* / Q000737:chemistry; D007477:Ions / Q000032:analysis / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D019155:Veterinary Drugs / Q000032:analysis* / Q000737:chemistry
chemical_list: D000871:Anthelmintics; D007477:Ions; D019155:Veterinary Drugs