Characterization and selectivity optimization on diol, amino, and cyano normal phase columns based on linear solvation energy relationships

Abstract

This paper describes the results of characterization and selectivity optimization on several normal phase columns by use of linear solvation energy relationships (LSERs). Retention data were obtained for a large set of judiciously selected test solutes on diol, amino, and cyano columns in a mobile phase of pure hexane. Based on the LSERs, the retention data were dissected into contributions from cavity formation/dispersive interactions, dipolar interactions, and hydrogen bond donor–acceptor interactions via both linear regression and principal component analysis. We find that the solute's hydrogen bond (HB) acceptor basicity is the predominant retention determining factors, particularly for diol and amino columns, and that its significance is directly related to the stationary phase acidity. However, the solute's size has a negative, but limited, influence on retention. Furthermore, the solute's hydrogen bond (HB) donor acidity and dipolarity also contribute significantly to retention, and cannot be neglected, as in the case of reversed-phase columns. Finally, the LSER results allow us to effectively predict the chromatographic selectivity on these normal phases, and it can be demonstrated that an increase in selectivity by about 10- to 1000-fold is expected when two solutes differ by only one polar functional group.