A liquid chromatography–mass spectrometry assay method for simultaneous determination of amiodarone and desethylamiodarone in rat specimens

A liquid chromatographic‐mass spectrometry (LC/MS) assay method was developed for the determination of amiodarone and desethylamiodarone in rat specimens. Analytes were extracted using liquid–liquid extraction in hexane. The LC/MS system consisted of a Waters Micromass ZQ™ 4000 spectrometer with an autosampler and pump. A C 18 3.5 µm (2.1 × 50 mm) column heated to 45°C was used for separation. The mobile phase consisted of methanol and 0.2% aqueous formic acid pumped at 0.2 mL/min as a linear gradient. Components eluted within 12 min. The concentrations of ethopropazine (internal standard), desethylamiodarone and amiodarone were monitored for m / z of 313.10, combination of 546.9 and 617.73, and 645.83, respectively. In plasma (0.1 mL), linearity was achieved between the peak area ratios and concentrations over the range of 2.5–1000 ng/mL for both amiodarone and desethylamiodarone ( r 2 > 0.999). The intraday and interday CV were equal or less than 18%, and mean error was <12%. Similarly, in homogenates containing 0.1 g of rat tissue, linearity was observed in standards ranging from 5 to 5000 ng/g. The method was successfully used to measure tissue and plasma concentrations of drug. The validated lower limit of quantitation was 2.5 ng/mL for drug and metabolite, based on 0.1 mL of plasma. Copyright © 2007 John Wiley & Sons, Ltd.