Influence of pressure on the retention of resorcinarene-based cavitands

The thermodynamics of the retention mechanism of resorcinarene-based cavitands in RPLC as well as the nature of the binding sites have been studied recently. In the present study, the influence of pressure on the retention of the cyclic tetramers on alkylsilyl and polar-embedded C₈ and C₁₈ stationary phases is investigated using aqueous methanol mobile phase. The pressure effect for cavity-shaped molecules has been scarcely studied so far. We observed that the retention factors of the analytes increased with the increase of the average column pressure (1-400 bar) when using restricting capillary tubes. The calculated molar volume changes were negative, between -ΔV_m = 5-19 mL/mol on all types of stationary phases. Comparing the different stationary phases, we found that the molar volume changes for both the apolar and more polar analytes were twice larger on the Hypersil BDS (base deactivated silica) than on the XTerra columns and they were independent of the length of the alkyl chains of the stationary phases.