Dependences of the Distribution Coefficients of Hydrophobic Solutes on Porous Methyl Methacrylate Resin on the Temperature and Methanol Content of the Eluent

Abstract

The elution curves of caffeine, vanillin, coumarin, and methyl paraben, which have different hydrophobicities, in a bed packed with porous methyl methacrylate resin, were measured by the pulse response technique using methanol-water mixtures with various methanol contents as the eluent in the temperature range of 30°C to 200°C. The more hydrophobic solutes eluted at a slower rate under all conditions. All solutes eluted faster with eluents with higher methanol contents and at higher temperatures. The distribution coefficients of the solutes to the resin under various conditions were evaluated by moment analysis of elution curves. The adsorption enthalpy changes, ΔH, of the solutes were estimated from the plots of the distribution coefficients versus the reciprocal of absolute temperature. For the eluents with methanol contents higher than 75%, the ΔH values of all solutes were practically zero. This indicates that the solutes scarcely adsorbed on the resin. For eluents with lower methanol contents, solutes were eluted at a slower rate and their ΔH values were more negative. When water was used as an eluent, elution behavior showed the opposite tendency.