title: Sensitive determination of oxybutynin and desethyloxybutynin in dog plasma by LC-ESI/MS/MS.
abstract: A sensitive and selective liquid chromatographic method coupled with tandem mass spectrometry (LC-MS/MS) was developed for the quantification of oxybutynin and desethyloxybutynin in dog plasma. Diazepam was used as internal standard, with plasma sample extracted using n-hexane and back-extracted using hydrochloric acid. A centrifuged lower layer (aqueous layer) was injected into a C(18) XTerra MS column (2.1 x 30 mm(2)) with 3.5 microm particle size. The analytical column lasted for at least 500 injections. The mobile phase was composed of 90% methanol, with flow rate at 200 microl/min. The mass spectrometer was operated in positive ion mode using electrospray ionization. Nitrogen was used as the nebulizer gas and argon was used as the collision gas. Using MS/MS with multiple reaction monitoring (MRM) mode, oxybutynin and desethyloxybutynin were detected without severe interferences from plasma matrix. Oxybutynin produced a protonated precursor ion ([M+H](+)) at m/z 358 and a corresponding product ion at m/z 142. Desethyloxybutynin produced a protonated precursor ion ([M+H](+)) at m/z 330 and a corresponding product ion at m/z 96. And internal standard (diazepam) produced a protonated precursor ion ([M+H](+)) at m/z 285 and a corresponding product ion at m/z 193. Detection of oxybutynin and desethyloxybutynin in dog plasma were accurate and precise, with detection limit at 0.1 ng/ml. This method has been successfully applied to a study of oxybutynin and desethyloxybutynin in dog plasma.
authors.affiliation: Department of Pharmacokinetics, Seoul Medical Science Institute, Seoul Clinical Laboratories, 7-14 Dongbinggo-dong, Yongsan-gu, Seoul 140-809, South Korea. novakims@yahoo.com
authors.forename: Hohyun
authors.initials: H
authors.lastname: Kim
authors.forename: Sang Beom
authors.initials: SB
authors.lastname: Han
mesh_terms: D000818:Animals; D018680:Cholinergic Antagonists / Q000097:blood* / Q000493:pharmacokinetics; D002853:Chromatography, Liquid / Q000379:methods*; D004285:Dogs; D008333:Mandelic Acids / Q000097:blood* / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D018680:Cholinergic Antagonists; D008333:Mandelic Acids; C032681:desethyloxybutynin; C005419:oxybutynin