The Thermodynamics of Chromatography - Interactions Between the Atoms of Hydrogen, Carbon, Chlorine and Bromine and an Exclusively Dispersive Stationary Phase > Page 25

Interactions Between the Atoms of Hydrogen, Carbon, Chlorine and Bromine and an Exclusively Dispersive Stationary Phase

It is clear that the standard energy of distribution of a solute between two phases can also be be assigned to specific interacting atoms providing suitable data is available. If an appropriate series of solutes are chosen such as the substituted methanes, containing different elements, (e.g.H, Cl and Br) and different numbers of atoms of each element (e.g. 1, 2, 3, and 4), GC retention measurements taken at different temperatures, can yield the standard enthalpies and entropies for the interaction of each substituent element with the stationary phase. Such data can, in turn, help elucidate the nature of the interactions and how they may differ from one element to another and influence phase selectivity. However, the thermodynamic data will only be valid (at least until more is known about mixed interactions) if one kind of interaction is solely active. If other interactions are present then it will be clear that, without making certain theoretical assumptions, the number of unknown parameters exceed the number of pertinent equations that can be derived and a practical mathematical solution is not possible.  Martire et al. (8) reported GC retention data for the following pertinent solutes using n-octadecane as the stationary phase and thus, only dispersive iteractions were significantly active

                             1.  Dichloromethane

                             2.  Chloroform

                             3.  Carbon Tetrachloride

                             4.  Dibromomethane

                             5.  Bromoform

                             6.  Carbon Tetrabromide

                             7.  Chlorobromomethane 

                             8.  Dichlorobromomethane

                             9.  Trichlorobromomethane

                             10. Dibromochloromethane