The non-dispersive functional group-solvent interaction monitored by HPLC

We have used a squalane adsorbed C-18 phase as presumably a bulk-like stationary phase to secure a simple partition mechanism for solute retention in reversed phase liquid chromatography, and have evaluated the nondispersive (specific) functional group-solvent interaction separately by measuring the retention data of carefully selected solutes in 60/40, 70/30, and 80/20 (v/v%) methanol/water eluents at 25,30,35,40,45, and 50 degrees C. We have found that the absolute magnitude of the carbonyl group (in acetophenone)-mobile phase specific interaction enthalpy is much greater than that of the hydroxyl group (in phenol)-mobile phase specific interaction enthalpy. If we consider the overall differential solute transfer free energy for a pair of polar and nonpolar solutes of the same size, the entropic contribution is dominant for the BT/phenol pair, and the enthalpic contribution, for the ethylbenzene/acetophenone pair. On the other hand, for a pair of nonpolar solutes, the entropic contribution to the differential free energy of solute transfer is much lower than the enthalpic contribution, and the variation in the differential entropy of solute transfer with respect to mobile phase composition is much smaller than the variation in the differential enthalpy, too.