Determination of β-artemether and its main metabolite dihydroartemisinin in plasma employing liquid-phase microextraction prior to liquid chromatographic–tandem mass spectrometric analysis

A method for the determination of artemether (ART) and its main metabolite dihydroartemisinin (DHA) in plasma employing liquid-phase microextraction (LPME) for sample preparation prior to liquid chromatography–tandem mass spectrometry (LC–MS–MS) was developed. The analytes were extracted from 1 mL of plasma utilizing a two-phase LPME procedure with artemisinin as internal standard. Using the optimized LPME conditions, mean absolute recovery rates of 25 and 32% for DHA and ART, respectively, were achieved using toluene–n-octanol (1:1, v/v) as organic phase with an extraction time of 30 min. After extraction, the analytes were resolved within 5 min using a mobile phase consisting of methanol–ammonium acetate (10 mmol L−1, pH 5.0, 80:20, v/v) on a laboratory-made column based on poly(methyltetradecylsiloxane) attached to a zirconized-silica support. MS–MS detection was employed using an electrospray interface in the positive ion mode. The method developed was linear over the range of 5–1000 ng mL−1 for both analytes. Precision and accuracy were within acceptable levels of confidence (<15%). The assay was applied to the determination of these analytes in plasma from rats treated with ART. The two-phase LPME procedure is affordable and the solvent consumption was very low compared to the traditional methods of sample preparation.