Study of retention mechanism reversed-phase liquid chromatography

The retention mechanism of a highly variegated solute set in reversed phase liquid chromatography was investigated using linear solvation energy relationships. Solute size and hydrogen bond acceptor basicity are the main retention-governing factors in mobile phases using acetonitrile, methanol and tetrahydrofuran as modifiers. Over the range of 50-80% (volume) water in mobile phase, these two solute terms become increasingly more important as the volume fraction of water is increased. Solute dipolarity/polarizability and hydrogen bond donor acidity are of minor influence in establishing retention, and their contributions stay virtually constant over the composition range studied. The studies indicate that large amounts of mobile phase components must be sorbed into the bonded phase, and that the mobile phase is not the sole factor governing the retention. Aliphatic and aromatic compounds were examined separately. Bonded phases of very different silanolphilicity were investigated.; The partitioning versus adsorption retention mechanism in reversed phase liquid chromatography was examined based on the free energy of transfer of a methylene group from organic aqueous mixtures to bulk hexadecane. Retention on both the monomeric and polymeric bonded phases with octyl chains or longer are dominated by a partitioning-like mechanism. An adsorption-like mechanism prevails on monomeric bonded phase with short bonded chains or with low surface coverage density. The retention mechanism becomes more adsorption-like as the length of the bonded chains decreases.; The validity of the frequently reported linear relationship between the slopes (S) and intercepts (ln k{dollar}spprimesb{lcub}rm w{rcub}{dollar}) for plots of logarithmic capacity factors against mobile phase volume fraction organic modifier in reversed phase liquid chromatography was investigated. The linear S-ln k{dollar}spprimesb{lcub}rm w{rcub}{dollar} relationship for a chemically variegated set of solutes may, under certain conditions, be a statistical artifact. Such linear relationships are rigorously valid when only a single retention-governing solute property varies within the set of solutes studied, or when various retention governing processes have the same compensation composition.; A liquid chromatographic method for the measurement of relative hydrogen bond basicities of dilute species was investigated. Solute retention on a phenolic functionalized stationary phase was evaluated using literature hydrogen bond basicity scales and steric hindrance parameter.