Stability of Silica-Based, Monofunctional C18 Bonded-Phase Column Packing for HPLC at High pH

Previous studies have shown that nonendcapped, monofunctional bonded-phase column packings made from silica supports prepared by the sol-gel method have surprising stability at up to pH 10 in certain mobile phases. Even when purged with NaOH at pH 12, these columns demonstrate properties that suggest that useful chromatographic separations might be feasible under such conditions. Separations at high pH (pH 10 or greater) are attractive for separating certain basic compounds. Such solutes would be in the free-base form, which would minimize potential deleterious interaction with unreacted silanol groups on the silica support. Results from this study indicate that use of lithium-based buffers may reduce the dissolution of silica supports and thus enhance column stability at high pH. Experiments also suggest that pH 12 separations with sol-gel silica supports are feasible, although such high pH operation limits column lifetime.