Prediction of retention in gas-liquid chromatography using the unifac group contribution method. I. Low-molecular-weight stationary phases

The UNIFAC group contribution method and its free volume modified version were used to calculate thermodynamic activity coefficients for a number of solutes at infinite dilution in a range of non-polymeric gas-liquid chromatographic stationary phases. Specific retention volumes and partition coefficients were calculated and used to predict relative retentions and the order of elution of the solutes and these were compared with corresponding experimental values. For non-polar stationary phases, the elution orders were correctly predicted, even for closely related isomers, except with very close retention volumes, although the UNIFAC and experimental partition coefficients differed by up to 20-50%, depending on the system. For polar phases and systems with strong specific interactions such as hydrogen bonding, the predictions differed greatly from the experimental values. The method may be useful for correlating results for non-polar phases but its wider predictive use awaits further development of the UNIFAC methodology.