High pH mobile phase effects on silica-based reversed-phase high-performance liquid chromatographic columns

Aqueous mobile phases above pH 8 often cause premature column failure, limiting the utility of silica-based columns for applications requiring high pH. Previous studies suggest that covalently bound silane ligands are hydrolyzed and removed by high-pH mobile phases. However, we found that the siloxane bonds for certain monomeric silanes are hydrolyzed very slowly from silica supports at pH 9–10. Therefore, bonded-phase packing degradation at high pH is a result mainly of silica support dissolution. The rate of column degradation for C18 columns is influenced not only by the type and purity of silica support, but also by the nature of the silane stationary phase. We found different rates of degradation for several commercial C18 columns. The relative rates of silica dissolution for these packings were determined by chemically measuring the silicate formed during column purging at high pH. The type and concentration of mobile phase organic modifier also significantly influences column degradation at high pH. Certain silica-based C18 packings can be used for long periods at pH 9 without significant changes in chromatographic properties. Results of this study better define the practical utility and limitations of silica-based columns in high pH environments.