PREP 2018 - 31st International Symposium on Preparative and Process Chromatography
Baltimore (MD), 8th-11th July 2018
David Pfister will present on "When adsorption models fail at describing ion-exchange chromatography"
Ion-exchange chromatography is certainly the most ancient type of chromatography there is. While M. Tswett is often credited the paternity of chromatography in 1901, the first traces of the use of ion-exchange chromatography date back to the Ancient Egypte. More than three thousand years ago, Moses was producing drinking water from sea water using sand to demineralize it. However, this is only in the 20th century, with the development of the Manhattan project that ion-exchange chromatography had its heyday. Nowadays, industrial processes based on ion-exchange chromatography can be found in many different sectors from the food industry for sugars softening, to the biopharmaceutical industry for protein purification.
From a modeling point of view, ion-exchange is conceptually different from its cousin adsorption. Indeed, the “exchange” mechanism is making all the difference. Because of the substitution of ions at the surface of the chromatographic medium with the ones present in the liquid phase, the solution chemistry, which includes acido-basic equilibria and complexation reaction, is strongly altered, thus affecting the retention of the different species in solution. However, there is quite often the tendency to try to describe ion-exchange equilibria with classical adsorption isotherms (Langmuir adsorption isotherms and alike) to simplify the problem and make the resolution of equations explicit. Although this can be a reasonable approximation in some cases, there are also numerous examples demonstrating the limits of this approach. From the simplest case of the measure of the “adsorption isotherm” of salt on a strong cation exchange resin, we will see that complex hysteresis phenomena are observed which cannot be explained by an adsorption mechanism. We will then increase the complexity of the system under investigation and show different phenomena that can only be understood by properly accounting for the ion-exchange mechanism.
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