Determination of adsorption isotherms on graphitized carbon black by zonal gas chromatography

A method for extracting the physico-chemical parameters from the analysis of the chromatographic elution peak profile is developed. From the set of differential equations of gas-chromatography, an analy- tical expression of the elution peak is given in the case of low concen- trations, when the isotherm can be replaced by a two term expansion. The model is a function of 4 parameters: the sample size (peak area), the apparent axial dispersion (band broadening), the slope and the curvature of the isotherm at origin. The variation of peak maximum with increasing amounts injected provides a convenient way of determining the first and second surface virial coeffi- cients of the adsorption isotherm. We have examined the validity of the model by studying the elution behavior of benzene and hexane on graphi- tized carbon black at different temperatures. The parameters of the adsorption isotherm determined by chromatography are compared with those obtained from static methods (ref. 1). In the case of a Langmuir type isotherm, the monolayer capacity of the adsorbate can be measured.