Improved silica-based column packings for high-performance liquid chromatography

Abstract

Undescribed adsorption of basic compounds and the low hydrolytic stability of alkyl bonded-phase ligands can be strongly affected by the existence of highly-acidic, essentially non-hydrogen bonded (or isolated) SiOH groups on silica packings. We have previously proposed that the support for stable silica reversed-phase packings with low adsorptivity for basic compounds should contain the highest, and not the lowest, number of homogeneously distributed, associated SiOH groups. To obtain such desirable supports we fully hydroxylate calcined silica by special techniques involving the dissolution and redeposition of silici acid. This rehydroxylation process results in no substantial change in the surface area or pore size of the silica support. Subsequently, the properties of these silicas were investigated by chemical, spectroscopic and chromatographic techniques. Fully hydroxylated silicas exhibit: (1) a larger number of associated silanols; (2) higher pH values; (3) markedly lowered adsorptivity for basic compounds; (4) significantly improved hydrolytic stability of bonded-phase ligands; and (5) increased mechanical stability. Large pore-size, reversed-phase packings made from this kind of support produced much better separations of basic peptides and proteins than conventional column packings.