Abstract
Factors controlling the retention of 28 solutes on 23 stationary phases are identified by multivariate analysis and related to dominant intermolecular interactions. The selectivity of the stationary phases is characterized by the partial molal Gibbs free energy of solution for specific test solutes identified by principal component analysis; nitrobenzene for orientation interactions and n-octanol for solvent proton acceptor interactions. No test solute with acceptable certainty was identified for solvent proton donor interactions. The partial molar Gibbs free energy of solution for a methylene group is a convenient parameter for assessing dispersive interactions. For highly cohesive phases, such as OV-275, TCEP, DEGS, QACES AND QTAPSO the selectivity parameters were found to be solute-size dependent. This size dependence can be removed by separating the free energy into a cavity term and an interaction term; the interaction term being independent of solute size. Using principal component analysis and cluster analysis the 23 stationary phases were classified into 5 groups based on the similarity of their capacity for specific intermolecular interactions with the phases squalane. QF-1, OV-225, OV-275 and QTAPSO behaving independently. The use of dendrograms is demonstrated to be a useful method for visualizing selectivity differences for chromatographic optimization.
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