CHROMATOGRAPHIC ACTIVITY OF RESIDUAL SILANOLS OF ALKYLSILANE DERIVATIZED SILICA SURFACES

Residual silanols on n-octadecylsilane derivatized silica surfaces hav e a pronounced effect on the chromatographic performance of reversed-p hase high-performance liquid chromatography (RP-HPLC) materials. The p resent study describes how the results of solid-state NMR investigatio ns on two commercially available reversed-phases for HPLC are verified chromatographically. One phase is a dimethyl-n-octadecylsilane deriva tized silica substrate (Rx-C-18), while the other is the same substrat e derivatized with di-isobutyl-n-octadecylsilane (''stable bond'', SB- C-18). Four column tests, taken from the literature, are performed in order to assess silanol activity and column hydrophobicity. It is conc luded that on the SB-C-18 phase, more residual silanols are analyte ac cessible and that the isobutyl groups contribute significantly to hydr ophobicity. Generally, the results of the solid-state NMR method for d etermining shielded and accessible residual surface silanols on RP-HPL C stationary phases could be confirmed.