Modifier influence on selectivity of reversed-phase HPLC systems

Correlation of partition constants of nine benzene derivatives in various gas - liquid systems, of which the solutions constitute binary mixtures of water and organic solvents methanol (MeOH), acetonitrile (ACN), tetrahydrofuran (THF), show high values of correlation factor. On the other hand, the correlation of retention, as log k (k - retention coefficient) of the same solutes in high performance reversed phase liquid chromatography (RPHPLC) systems with stationary phase of the C18 type and eluents of similar composition as liquids in the gas - liquid partition systems, reveal much smaller values of correlation factor. The comparison of these correlation data leads to the inference that interaction of the solute in the stationary phase, especially with sorbed modifier, is responsible for selectivity variation when the modifier is changed in the binary mobile phase of the RPHPLC system. This behavior is additionally confirmed by the retention correlation of phenolic acids for RPHPLC system with the modifiers investigated.