Determination of benidipine hydrochloride in human plasma by capillary column gas chromatography—negative ion chemical ionization mass spectrometry

Abstract

A highly sensitive and specific determination method of a new calcium antagonist, benidipine hydrochloride, in human plasma has been developed using capillary column gas chromatography with negative ion chemical ionization mass spectrometry. A deuterated analogue of benidipine hydrochloride was used as an internal standard. Benidipine hydrochloride was extracted from plasma with diethyl ether under basic conditions, back-extracted with 0.5 M sulphuric acid, and reextracted with diethyl ether under basic conditions. For gas chromatography, a solventless injection port was used, and the whole extract was injected. Fragment ions at m/z 488 (benidipine) and m/z 493 (internal standard) were used as monitoring ions for selected-ion monitoring. The detection limit was 0.02 ng/ml with 0.5 ml of plasma. The coefficient of variation of intra-day assay was 17.4% and 12.1% at the 0.02 and 0.1 ng/ml levels, respectively. This method has made it possible to detect the plasma level of unchanged drug up to 12 h after an 8-mg oral dose of benidipine hydrochloride to humans.