PEAK COMPRESSION IN STEPWISE PH ELUTION WITH FLOW REVERSAL IN ION-EXCHANGE CHROMATOGRAPHY

Peak compression (increase of peak concentration and reduction of peak tailing) due to a step pH change or flow reversal has been studied theoretically and experimentally. Linear and nonlinear local equilibrium models and a detailed rate model have been used to analyze the mechanisms of peak compression. The models have been tested with L-lysine data of a cation exchange system. Peak compression, which is significant when a large difference in affinities is induced for a large dilute pulse, can achieve high resolution using relatively large sorbent particles. It is shown experimentally that a dilute lysine pulse can be compressed to about 35 times its feed concentration. For multicomponent separations, compression prior to separation can give a shorter cycle time and higher product purity than linear gradient elution. Flow reversal coupled with selectivity reversal in stepwise elution allows separation to occur during both forward and reversed elution, resulting in increased column utilization. In general, optimized stepwise elution with flow reversal can give better separation than linear gradient elution. The results are useful in optimizing column design and increasing column efficiency in downstream bioprocessing.