CHARACTERIZATION OF C-18-BONDED SILICAS FOR SOLID-PHASE EXTRACTION BYSOLID-STATE NMR-SPECTROSCOPY

Si-29 and C-13 cross-polarisation magic-angle-spinning (CP-MAS) NMR sp ectroscopy have been used to characterise a total of seven C-18-bonded silicas used for solid-phase extraction. Wide variations were observe d in the extraction properties of these silicas for basic analytes suc h as the drug propranolol. These differences depended upon the degree of carbon loading of the phases and whether or not endcapping had been performed. The different properties of the phases appear to correlate well with the differences observed using CP-MAS NMR. This demonstrate s the utility of such techniques as a means of further understanding t he underlying mechanisms responsible for the observed extraction prope rties of the phases.