Measurement of Thermodynamic Equilibria by Chromatography

After a brief recall of the chromatographic principles, t h e different applications of gas chromatographic measurements of thermodynamic equilibria were reviewed. Gas and liquid chromatographies are now well known and elegant methods for measuring the physicochemical properties and phase equil ibrium thermodynamic constants. Although fundamentally a dynamical method and mostly known as a powerful separation technique, chromatography can be schematized by a succession of equilibria of a chemical species partitioning between a mobile phase and a fixed liquid or solid stationary phase. It can be operated in either inf inite di lut ion or f inite concentration conditions and permits to collect a large number of data for calculating molecular interactions for solutes which are either rare or available at the trace level. Gas chromatography permits the measurement of gas adsorption isotherms, gas-liquid equilibria, molecular diffusion and interaction virials. The modelization of successive partition equilibria occuring in the chromatographic column leads to rather simple expressions of differential enthalpy, entropy, free energy of adsorption or solution, variation of heat capacity, complexation constant, second virial coefficients, gas-solid and gasliquid isotherms and also binary or ternary equilibria. The possibilities of High Performance-Liquid Chromatography to investigate adsorption from solutions and chemical equilibria are also discussed.