A GC-MS Method for the Determination of Isoxsuprine in Biological Fluids of the Horse Utilizing Electron Impact Ionization

J. M. Bosken, A. F. Lehner, C. G. Hughes, W. E. Woods, F. C. Camargo, J. D. Harkins, J. Boyles, T. Tobin

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Isoxsuprine is used to treat navicular disease and other lower-limb problems in the horse. Isoxsuprine is regulated as a class 4 compound by the Association of Racing Commissioners, International (ARCI) and, thus, requires regulatory monitoring. A gas chromatography-mass spectrometry method utilizing electron impact ionization was developed and validated for the quantitation of isoxsuprine in equine plasma or equine urine. The method utilized robotic solid-phase extraction and tri-methyl silyl ether products of derivatization. Products were bis-trimethylsilyl (TMS) isoxsuprine and tris-TMS ritodrine, which released intense quantifier ions m/z 178 for isoxsuprine and m/z 236 for ritodrine that were products of C-C cleavage. To our knowledge, this procedure is faster and more sensitive than other methods in the literature. Concentrations in urine and plasma of isoxsuprine were determined from a calibrator curve that was generated along with unknowns. Ritodrine was used as an internal standard and was, therefore, present in all samples, standards, and blanks. Validation data was also collected. The limit of detection of isoxsuprine in plasma was determined to be 2 ng/mL, the limit of quantitation of isoxsuprine in plasma was determined to be < 5 ng/mL. The mean coefficient of determination for the calibrator curves for plasma was 0.9925 ± 0.0052 and for calibrator curves for urine 0.9904± 0.0075. The recovery efficiencies at concentrations of 50, 200, and 300 ng/mL were 76%, 73%, and 76%, respectively, in plasma and 92%, 89%, and 91% in urine.

Original languageEnglish
Pages (from-to)27-34
Number of pages8
JournalJournal of Analytical Toxicology
Issue number1
StatePublished - 2004

Bibliographical note

Funding Information:
* Publication # 263 from the Equine Pharmacologya nd ExperimentalT herapeuticsP rograma t the Maxwell H. Gluck Equine ResearchC entera nd the Departmento f VeterinaryS cience, University of Kentucky. Published as KentuckyA gricultural ExperimentS tation Article #02-14-184 with the approval of the Deana nd Director, College of Agriculture and KentuckyA gricultural ExperimentS tation. Supported by grants from The Kentucky Equine Drug Council and The Kentucky Racing Commission, Lexington,K Y and by researchs upport from the National, Canadian, Kentucky, Charles Town,O hio, Arkansas,M ichigan, Pennsylvania,O ntario, Alabama, Florida, and NebraskaH orsemen'sB enevolenta nd ProtectiveA ssociationsa nd Mrs. John Hay Whitney. Author to whom correspondences hould be addressed.E -mail:j reboskO@ulo/.edu.

ASJC Scopus subject areas

  • Analytical Chemistry
  • Environmental Chemistry
  • Toxicology
  • Health, Toxicology and Mutagenesis
  • Chemical Health and Safety


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