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 requiri ng high PH. Previous studies suggest that covalently bound silane liga nds are hydrolyzed and removed by high-pH mobile phases. However, we f ound that the siloxane bonds for certain monomeric silanes are hydroly zed very slowly from silica supports at pH 9-10. Therefore, bonded-pha se packing degradation at high pH is a result mainly of silica support dissolution. The rate of column degradation for C-18 columns is influ enced not only by the type and purity of silica support, but also by t he nature of the silane stationary phase. We found different rates of degradation for several commercial C-18 columns. The relative rates of silica dissolution for these packings were determined by chemically m easuring the silicate formed during column purging at high pH. The typ e and concentration of mobile phase organic modifier also significantl y influences column degradation at high pH. Certain silica-based C-18 packings can be used for long periods at pH 9 without significant chan ges in chromatographic properties. Results of this study better define the practical utility and limitations of silica-based columns in high pH environments.