ABSTRACT
Comparison of Gas-Solid and Liquid-Solid Systems An attempt was made to elucidate some thermodynamic properties of the adsorption equilibrium in RPLC by comparing the values of Qst measured for the same adsorbent in gas-solid and liquid-solid adsorption systems. Figure 18 illustrates the van't Hoff plot of the equilibrium data measured in the gas-solid system [61]. The resulting values of Q8t are listed in Tables 1 and 4 [61]. The ratios of -Q8t to the heat of vaporization of the solute (l:l.Hu) range between,..,., 1.1 and 1.3, a relatively narrow range for compounds having a wide range of molecular weights, polarities, and vapor pressures. This result is probably reasonable because gas-solid adsorption on a nonpolar surface resembles vaporization with the additional interaction between sample molecules and the surface of the stationary phase in the adsorption process. The values of -Q8t in gas-solid systems are large compared with those measured in liquid-solid systems, suggesting that Qst is significantly influenced by the presence of a sol· vent. Similar to the analysis concerning the solvent effect on K, the phenomenon may be interpreted by applying the solvophobic theory.
