Estimating diffusion coefficients for alkylbenzenes and alkylphenones in aqueous mixtures with acetonitrile and methanol.

The accuracy of various empirical approximation methods of estimating the diffusion coefficients of alkylbenzenes and alkylphenones in acetonitrile (ACN)/water and methanol (MeOH)/water solvent systems is reported. Diffusion coefficients for these solutes have been measured over a wide range of solvent compositions and temperatures. A novel empirical modification of the Wilke-Chang method has been developed by correlating measured values with solute and solvent parameters. The correlation, along with the Wilke-Chang and Scheibel correlations, was examined by comparing the computed diffusion coefficients with the measured values. We find that the percent errors of the proposed correlations are no greater than 10% for both ACN/water and MeOH/water systems and that the accuracy of the correlation is 2-3-fold better than those of the other two correlations. We recommend the use of this correlation with the above homologous series of solutes for the evaluation of column performance in reversed-phase liquid chromatography.