Abstract
To produce a large mass spectral signal in the analysis of basic drugs by high performance liquid chromatography/electrospray ionization mass spectrometry (HPLC/ESI-MS), a high percentage of organic solvent is needed in the mobile phase. With the commonly used reversed phase columns (C18, C8 and C4) high concentrations of organic solvents cannot be used; therefore other stationary phases were investigated. The stationary phases investigated had phenyl ring structures; phenyl (Ph) and pentafluorophenyl (PFP) which were bonded directly to the silica backbone and other phases, pentafluorophenylpropyl (PFPP), phenylpropyl (PhP) and tolylpropyl (TP), which were attached to the silica via a propyl chain. The effects of these stationary phases on retention, peak shape and size of the signal in the mass spectrometric analysis of a selected group of basic drugs, tricyclic antidepressants (TCAs) and beta-blockers, were evaluated and compared with those obtained on a C18 column. The PFPP column was found to give the best results. The basic drugs were adequately retained with retention times greater than 2 minutes when the PFPP column was used with mobile phases of high concentrations of organic solvents. Thus the endogenous interferences could be eliminated and the analysis time was still rapid enough to have a high throughput. Most importantly, a mobile phase of 90% acetonitrile could be used which allowed easy desolvation in the ESI interface and provided good peak shapes. In addition, ion-pairing reagents and ion-suppressing agents which suppress the signal in ESI-MS were not required. The best results were obtained using a 1 cm column and a flow rate of 0.9 mL/min. With the PFPP stationary phase and a mobile phase of 90% acetonitrile, the HPLC/ESI mass spectral signal of the beta-blocker, oxprenolol, was increased by a factor of 16 compared with the C18 phase with only 12% acetonitrile in the mobile phase. Copyright 1999 John Wiley & Sons, Ltd.
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