Optimized stationary phases for the high-performance liquid chromatography-electrospray ionization mass spectrometric analysis of basic pharmaceuticals

Stationary phases were investigated for HPLC coupled with electrospray ionization mass spectrometry (ESI-MS) for the analysis of basic drugs. Tricyclic antidepressants (TCAs) and beta-blockers were used as model solutes. The functional groups, pentafluorophenyl (PFP), OH, CN or CH3 were attached to the silica via a propyl chain. The effects of these stationary phases as well as C-8 and C-18 phases on retention and peak shape of the basic drugs were studied. The CN and PFP phases adequately retained (t(R) of 2 to 6 min) the basic drugs when the mobile phase was composed of 90% acetonitrile, whereas with the C-4, C-8 and C-18 phases, less than 40% acetonitrile had to be used to provide adequate retention of the basic drugs. Because acetonitrile provides better desolvation in ESI than an aqueous solvent, it produces an increased MS signal. As an example of the HPLC-ESI-MS analysis of the beta-blocker, pindolol, on a CN phase, the use of 90% acetonitrile in the mobile phase increased the ESI-RIS signal by 790% when compared to a C-18 phase which could use only 5% acetonitrile in the mobile phase for retention of the solute. In addition, the CN and PFP phases provided better peak shape than the OH phase and the hydrophobic phases (C-4, C-8 and C-18) and ion-pairing or ion-suppressing agents were not required. The retention behavior of the TCAs and beta-blockers on each of the phases is described. (C) 2000 Elsevier Science B.V. All rights reserved.