Interactions among the stationary phase, the mobile phase, and the solute in liquid chromatographic systems

Interactions among the stationary phase, the eluent, and the solute in liquid chromatography were studied. A strong dependence of the stationary phase properties on the eluent composition may arise from their interactions.; The solvatochromic comparison method, which gives estimates for the dipolarity-polarizability {dollar}(pisp{lcub}*{rcub}),{dollar} the hydrogen-bonding acidity {dollar}(alpha),{dollar} and the hydrogen-bonding basicity ({dollar}beta){dollar} of a solvent, was used to study the properties of silica in n-hexane-chloroform or n-hexane-ethyl ether mixtures. A high {dollar}pisp{lcub}*{rcub}{dollar} and {dollar}alpha,{dollar} and a low {dollar}beta{dollar} were obtained for silica in n-hexane. The {dollar}pisp{lcub}*{rcub}{dollar} and {dollar}alpha{dollar} values for silica were not affected by the addition of chloroform into n-hexane. The {dollar}beta{dollar} value for silica decreased with increasing amounts of chloroform. The {dollar}pisp{lcub}*{rcub}{dollar} value for silica decreased with increasing contents of ethyl ether. The decrease in {dollar}pisp{lcub}*{rcub}{dollar} and {dollar}beta{dollar} values may result from the competition between the polar solvent and the solvatochromic dyes for the strong adsorption sites on silica.; UV-Vis spectra of N,N-dimethyl-4-nitroaniline in n-hexane-ethyl ether mixtures were used to elucidate solute-solvent interactions. Target factor analysis indicated that solute-solvent interactions in a binary solvent can only be reproduced using three or four, instead of two, significant factors, which is probably caused by the existence of various microenvironments in n-hexane-ethyl ether mixtures.; Optical transmittance was established to study the wetting of alkyl bonded silicas in organic-water mixtures. When the organic solvent content, {dollar}varphi,{dollar} was high, alkyl bonded silica was wetted and well solvated. With decreasing {dollar}varphi,{dollar} alkyl bonded silica became less solvated. When {dollar}varphi{dollar} was lower than the nonwetting limit, alkyl bonded silica became nonwetted. With increasing {dollar}varphi,{dollar} nonwetted alkyl bonded silica remains nonwetted until {dollar}varphi{dollar} reaches the rewetting limit, which is much higher than the nonwetting limit. Wetting hysteresis, which coexists with slow kinetics, was observed. Different alkyl bonded phases have different wetting behaviors. Much longer equilibration time is required if the stationary phase is nonwetted or not well solvated. Both the surface dipolarity and solute retention are affected by the wetting of the stationary phase.