RAPID LIQUID-CHROMATOGRAPHIC MASS-SPECTROMETRIC ASSAY FOR OXYMETAZOLINE IN WHOLE RAT-BLOOD

A rapid HPLC-electrospray mass spectrometric assay for the quantitatio n of oxymetazoline in whole rat blood has been developed. Sample prepa ration was a single liquid-liquid extraction after addition of a deute rated internal standard (IS) and pH adjustment. An aliquot of reconsti tuted extract was injected onto a narrow-bore octadecyl reversed-phase column at a flow-rate of 400 mu l/min. Using a 20:1 post-column split , 5% of the eluent was introduced into the mass spectrometer interface . Elution of the analyte and IS occurred in less than 2 min. This rapi d separation was made possible because of the sample cleanup and the s electivity of the mass spectrometric detection. The [M + H](+) ions fo r oxymetazoline (m/z 261) and [H-2(9)]oxymetazoline (mit 270) were det ected using selected ion monitoring. The linear range of the assay was 0.67-167 ng/g of blood and the limit of quantitation with a 0.30-g sa mple was 1.0 ng/g. The assay permitted the analysis of nine samples pe r hour with the requisite sensitivity and selectivity and was used to determine the blood pharmacokinetics of oxymetazoline in rats dosed vi a intravenous and intranasal routes.