Revised solute descriptors for characterizing retention properties of open-tubular columns in gas chromatography and their application to a carborane–siloxane copolymer stationary phase

An iteration procedure is used to calculate revised solute descriptors for 103 varied compounds suitable for characterizing the retention properties of stationary phases for gas chromatography using the solvation parameter model. The iteration procedure utilizes a database of retention factors obtained on up to 39 open-tubular columns and up to five temperatures in the range 60–140 °C for the 103 solutes. The average of the standard deviation [Σ(log kexp – log kcalc)2/(nc – 1)]0.5 where log kexp is the experimental retention factor, log kcalc the model predicted retention factor, and nc the total number of retention factors) on all columns is 0.018 for the revised solute descriptors compared with 0.045 for the original values. When used to characterize the retention properties of six open-tubular columns selected to represent different selectivity groups the revised solute descriptors afford improved values for the multiple correlation coefficient and standard deviations of the system constants, and about a three-fold improvement in the standard error of the estimate compared with the original solute descriptors. The revised solute descriptors were used to model retention on the carborane–siloxane copolymer stationary phase Stx-500. This phase has low cohesion, is weakly electron lone pair repulsive, weakly dipolar/polarizable, and weakly hydrogen-bond basic. It has no hydrogen-bond acidity. Its separation properties are similar to those of the poly(diphenyldimethylsiloxane) stationary phases containing 5% diphenylsiloxane monomer, but it is not selectivity equivalent to these phases, being more dipolar/polarizable and a weaker hydrogen-bond base.