SI-29 NMR MODEL DISSOLUTION STUDY OF THE DEGRADATION OF REVERSED PHASES FOR HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

In order to simulate aging under chromatographic conditions, mono-, di -, and trifunctional octyl and octadecyl derivatized reversed-phase hi gh-performance liquid chromatography silicas were exposed to the very aggressive mobile phase-like medium of 6 M NaOH in MeOH/H2O (50/50 v/v ). Si-29 NMR was used to study the dissolution characteristics of thes e phases by monitoring the concentrations of the dissolving silane and silica structures. Dissolution products of alkylchlorosilanes were us ed as model compounds for assignment purposes. Octadecyl phases appear ed to degrade by dissolution of the silica substrate; octadecylsilane structures were shown to be insoluble under the experimental condition s. Monofunctional octyl phases were shown to deteriorate through initi al dissolution of monomeric ligand silane particles, whereas for difun ctional octyl phases, the silica backbone appeared to dissolve with th e silane ligands still attached. The latter mechanism was also observe d for the trifunctional octyl phases, but these phases resemble octade cyl phases, probably because the free ligand silane particles are almo st insoluble and the major cause of phase degradation is dissolution o f the silica substrate.