Propagation of Signals of Finite Concentration in Gas Chromatography. II. Study of the Discontinuities and Their Conditions of Stability

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Abstract
The study of a quasi-ideal chromatography model at finite concentration shows the existence of stable discontinuities, resulting either from sorption or isotherm effects. A set of conditions, illustrated in a diagram, determines the conditions of stability of these discontinuities. Solution thermodynamics shows that there exist three possible modes of peak migration. In all cases a progressive variation of the experimental conditions (pressure or temperature of the column) allows passage from one of these modes to another. One of these three possible modes, the double-shock mode, has not been described previously. It is characterized by front and rear stable discontinuities, and its importance rests on the fact that it corresponds to the minimum band broadening. This mode is observed for a column temperature which is near the boiling point of the solute under the average pressure of the carrier gas. The results also show that the derivation of equilibrium isotherms from the deformation of the peaks obtained with large sample sizes is not valid generally.