Reversed-phase liquid chromatography with microspherical octadecyl-zirconia bonded stationary phases

Microspherical zirconia particles were synthesized and surface modified with octadecylsilane compounds for reversed-phase high-performance liquid chromatography. Monomeric and "polymeric" octadecyl-zirconia bonded stationary phases were obtained by reacting the support with octadecyldimethylchlorosilane or octadecyltrichlorosilane, respectively. The surface coverage of the zirconia-based stationary phases with octadecyl functions was approximately the same as that of octadecyl-silica sorbents. These phases were evaluated in terms of reversed-phase chromatographic properties with non-polar, slightly polar and ionic species over a wide range of mobile phase composition and pH. Monomeric octadecyl-zirconia with end-capping exhibited some metallic interactions with both basic and acidic solutes, but these interactions were greatly reduced in the presence of competing agents (e.g., tartrate ions) in the mobile phase. The "polymeric" octadecyl-zirconia sorbents exhibited higher retention than the monomeric ones with the various solutes investigated, and their residual absorptivities toward acidic solutes were much lower. The retention of non-polar and slightly polar aromatic compounds was quasi-homoenergetic on both types of octadecyl-zirconia stationary phases. Stability studies conducted at extreme pH conditions (pH 2.0 and pH 12.0), have shown that "polymeric" octadecyl-zirconia sorbents are more stable than their monomeric counterparts. These stationary phases were quite useful in the separation of polycyclic aromatic hydrocarbons, alkylbenzene and phenyl alkylalcohol homologous series, oligosaccharides, dansyl-amino acids, peptides and proteins.