ANALYSIS OF NONEQUILIBRIUM ADSORPTION DESORPTION-KINETICS AND IMPLICATIONS FOR ANALYTICAL AND PREPARATIVE CHROMATOGRAPHY

The assumption of local equilibrium in liquid chromatography can give misleading results when applied to high-affinity solutes, such as proteins, or other macromolecules. When adsorption or desorption becomes the rate-limiting step in a system, a number of symptoms will be present: symmetric and asymmetric spreading of waves, slow development of constant pattern, apparent loss of capacity, loss of coherence, and changes in interference patterns for multiple solutes. These results can reduce product purity and introduce serious errors into parameter estimation. These effects are predictable for any affinity and capacity combination if the dimensionless group approach developed herein is applied. By using a rate model of chromatography, we show how a system with nonequilibrium adsorption/desorption kinetics behaves when the controlling rate changes from kinetic to one or more mass-transfer rates and we give guidelines on scaling up processes efficiently by minimizing the nonequilibrium effects.