Retention in hydrophobic interaction chromatography and dissolution of nonpolar gases in water.

The retention data of dansyl amino acids in hydrophobic interaction chromatography (HIC) is interpreted in terms of physicochemical properties of the eluites and solvent and the results are compared to data for the dissolution in water of nonpolar gases. Isothermodynamic temperatures, certain linear relationships between thermodynamic quantities and molecular structure as well as the hermeneutics of the solvophobic theory are employed for data analysis. van't Hoff plots of the retention data with dansyl amino acids are curved and intersect at the isoenergetic temperature, indicative of enthalpy-entropy compensation. The isoenthalpic and isoentropic temperatures are also evaluated and the three isothermodynamic temperatures are found to fall in the same narrow ranges as those for the dissolution of gases in water. Plots of thermodynamic quantities for the retention in HIC against the nonpolar molecular area are linear and thus allow the evaluation of enthalpy, entropy, Gibbs energy and heat capacity changes per unit nonpolar surface area of dansyl amino acids. By employing the solvophobic theory thermodynamic expressions are derived in terms of the nonpolar molecular area and interfacial tension. Using these expressions and n-heptane as model compound it was found that the above group molecular parameters are nearly identical for the retention in HIC and the dissolution of gases in water, thus confirming the mechanistic identity of the two processes.