Quantitation of iptakalim in human plasma by high-performance liquid chromatography–tandem mass spectrometry

This paper describes a rapid and sensitive analytical method for the quantitation of iptakalim, a novel antihypertensive drug, in human plasma. The method is based on liquid chromatography–tandem mass spectrometry (LC–MS/MS) using sildenafil as internal standard. Sample preparation involved liquid–liquid extraction with dichloromethane–diethyl ether (2:3, v/v) in a basic environment. Chromatography was carried out on an amino column with a mobile phase consisting of acetonitrile–water (55:45, v/v, water containing 0.5% formic acid). Detection employed electrospray ionization (ESI) tandem mass spectrometry in the multiple-reaction-monitoring (MRM) mode. The assay was linear in the concentration range of 0.5–100 ng/ml with a lower limit of quantitation (LLOQ) of 0.5 ng/ml. Intra- and inter-day precision (R.S.D.) were <4.5% and <12.0%, respectively and the accuracy (R.E.) was in the range ±5%. The method was successfully applied to a single oral dose pharmacokinetic study in human volunteers.