Determination of the Surface Thermodynamic Characteristics of Phthalate Plasticizers by Inverse Gas Chromatography

The dispersive component of surface energy (γsd) and Lewis surface acid–base parameters (Ka, Kb) for phthalate plasticizers, including dimethyl phthalate, di-n-butyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, and diisodecyl phthalate, were determined by inverse gas chromatography (IGC) at infinite dilution. The IGC study was performed with an oven temperature varying between 313.15 and 343.15 K. Polar and nonpolar probes were used to quantify the solute–sorbent systems. Experimental data showed that the difference between the γsd values calculated by two methods (Schultz and Dorris and Gray) increases with increasing temperature. The acid–base parameters indicated that the surfaces of five examined phthalate plasticizers can be considered as amphoteric with a dominant basic character, and the Ka and Kb values ranged from 0.35 to 0.36 and 1.20 to 1.25, respectively. It was also found that the γsd value increased and the Lewis surface basicity (Kb/Ka) decreased with an increase of the alkyl chain length grafted onto the plasticizers. It is confirmed that IGC was useful for surface characterization and can be used to provide instructive thermodynamic information over a wide temperature range.