Investigation of lacidipine, a new 1,4-dihydropyridine antihypertensive agent and three chemically related compounds by means of chemical ionization, mass spectrometry and collision-induced dissociation

Abstract

Chemical ionization of two 1,4-dihydropyridines, lacidipine and its Z-isomer, and their corresponding pyridines in three different reagent gases and the collision-induced dissociation (CID) of their respective mass-selected protonated molecular ions in the collision energy range 10–200 eV were performed on a multiple quadrupole instrument. The weakness of the Breasted acid NH4+ as a protonating agent is clearly manifested in one of the ammonia positive-ion chemical ionization (CI+) mass spectra which displays the addition ion, [M + NH4]+, as the favoured reaction channel. The stereochemistry of the precursor molecules, the exothermicity of the protonation process and the threshold of certain dissociation channels as a function of the collision energy are among the arguments invoked to explain some of the observed differences between the CI+ mass spectra and the CID data of the different isomers investigated. In an attempt to present a more comprehensive study, some high-performance liquid chromatographic retention times and resolutions are also given.