Desorption chemical ionization, thermospray, and fast atom bombardment mass spectrometry of dihydropyridine in equilibrium with pyridinium salt-type redox systems.

Trigonellyl-substituted (pyridinium salt type) compounds decompose during sample introduction using desorption chemical ionization (DCI) and thermospray (TSP) ionization. Thermal dequaternization is the main degradation process in DCI, while hydrolytically sensitive bonds are subject to cleavage in the TSP source, and dequaternization and reduction to the dihydropyridine analogues are also observed. Fast atom bombardment (FAB) is the suggested method of ionization because of its ability to provide an intense intact cation. The neutral dihydropyridine analogues can be effectively ionized by DCI and TSP. These methods are recommended, because bombardment-induced oxidation produces artifacts and shows a matrix effect in positive FAB.