INFLUENCE OF TEMPERATURE ON THE MECHANISM BY WHICH COMPOUNDS ARE RETAINED IN GAS-LIQUID-CHROMATOGRAPHY

The influence of temperature on the retention mechanism and solvation interactions of 46 varied solutes in 10 representative stationary phas es of different polarity within the temperature range of 60 to 140 deg rees C is discussed. Gas-liquid partition is shown to the dominant ret ention mechanism for most solutes with inrterfacial adsorption of incr easing importance at low phase loadings, low temperatures and for solu tes of different polarity to that of the stationary phase. Guidelines are presented for predicting those conditions for which interfacial ad sorption is likely to be a significant retention mechanism. A cavity m odel is used to characterize the solvation process in terms of the fre e energy contributions to solvation from the cavity-dispersion interac tions and the sum of the remaining polar interactions. As a function o f temperature it is shown that the contribution from polar interaction s are only weakly temperature dependent over the temperature range stu died while the cavity-dispersion interactions term shows a much more s ignificant variation becoming less favorable for solute transfer at hi gher temperatures. In all cases, the contribution of the cavity-disper sion interactions term is favorable for solute transfer from the gas p hase to the liquid phase. Principal component analysis is used to iden tify the factors contributing to the solvation process and their indiv idual temperature dependence. In the case of the cavity-dispersion int eractions term one factor accounts for more than 99.7% of the total va riance. Three factors are identified as contributing to the polar inte ractions term. The first principle component accounts for more than 95 % of the total variance at all temperatures and by correlation with ot her independent scales of dipolarity/polarizability is identified as r epresenting the contribution from orientation and induction interactio ns. The two remaining principal components are shown to represent hydr ogen-bond formation and charge-transfer complexation involving systems with pi-electrons. The temperature dependence of the principal compon ents provides insights into the general role of polar intermolecular i nteractions on the solvation process and their temperature variation.