Solvation in weak complexing n-octyl phthalate and n-octyl tetrachlorophthalate solvents by gas chromatography

The solution properties of a varied group of solutes in di-n-octyl phthalate and di-n-octyl tetrachlorophthalate over the temperature range 60 to 120 degrees C were studied by gas chromatography. The solvation parameter model was used to assign the contribution of individual intermolecular interactions to the gas-liquid partition coefficients. The dominant interaction was dispersion with only small contributions from dipole-type interactions, n- and pi-electron donor/acceptor interactions (for the tetrachlorophthalate ester only), and solvent hydrogen-bond base interactions. Neither phthalate ester exhibited solvent hydrogen-bond acid properties. Complexes formed between solutes and these phthalate ester solvents are likely to be of the Van der Waals type, perhaps augmented by dipole-type interactions and hydrogen-bond complexation with hydrogen-bond acid solutes. In addition, n- and pi-electron complexation interactions, in the temperature range studied, may contribute to complex formation with the tetrachlorophthalate ester, but are too weak to be the dominant interactions involved. In general, the range of chromatographic selectivity obtainable through exploitation of the phthalate and tetrachlorophthalate nucleus does not warrant their selection as building blocks for new polymer-supported phases with the expectation of providing opportunities to extend the selectivity range of existing gas chromatographic stationary phases. In addition, the influence of interfacial adsorption as a retention mechanism for the determination of solvent properties and as a potential source of disagreement between reported solvent properties for the phthalate esters is discussed.