Characterization of C-18-bonded liquid chromatographic stationary phases by Raman spectroscopy: the effect of mobile phase composition

Raman spectroscopy is used to examine the effect of mobile phase compositio n on the orientation of octadecyl-bonded silica-based reversed-phase liquid chromatographic (RPLC) stationary phase ligands. The effect of Ligand bond ing density is also investigated. The present experimental set-up utilizes a direct, noninvasive, on-column approach to examine the solvent dependent conformational behavior of the bonded Ligands under flow-rate and back pres sure conditions similar to those used during conventional RPLC measurements . Neat, single-component, mobile phase solvents including water, acetonitri le, methanol and chloroform are used to investigate the hypothesized collap sing and extension of stationary phase ligands with changes in mobile phase composition. No evidence of phase collapse was observed upon changing the mobile phase composition from an organic to an aqueous content. Also, Raman spectroscopic measurements allowed the differentiation between associated and free acetonitrile solvent. (C) 2000 Elsevier Science BN. All rights res erved.