DETERMINATION OF NORDIHYDROCAPSAICIN IN RABBIT PLASMA BY LIQUID CHROMATOGRAPHY-ELECTROSPRAY MASS SPECTROMETRY

A simple and selective liquid chromatography mass spectrometry (LC-MS) method for determination of nordihydrocapsaicin in rabbit plasma was developed and validated over the concentration range of 10-2000 ng/mL. After addition of midazolam as internal standard (IS), protein precipitation with acetonitrile was used as sample preparation. Chromatographic separation was achieved on a Zorbax SB-C18 (2.1mm x 150 mm, 5.0 mu m) column with acetonitrile-0.1% formic acid as mobile phase with gradient elution. Electrospray ionization (ESI) source was applied and operated in positive ion mode; selective ion monitoring (SIM) mode was used for quantification using target fragment ions m/z 294 for nordihydrocapsaicin and m/z 326 for the IS. Lower limit of quantification (LLOQ) for nordihydrocapsaicin was 10 ng/mL. Mean recovery of nordihydrocapsaicin from plasma was in the range 92.0-96.6%. Relative standard deviation (RSD) of intra-day and inter-day precision were both less than 9%. The LC-MS method successfully applied to a pharmacokinetic study of nordihydrocapsaicin after intravenous administration of single dosage 5mg/kg to rabbits.