The optimization of preparative separations by overloaded gradient elution chromatography was studied on a theoretical basis. Band profiles of binary mixtures were calculated as numerical solutions of the equilibrium- dispersive model. A nonlinear simplex method allowed the determination of the optimum experimental conditions. The product of the production rate and the recovery yield was used as an objective function. The optimum experimental conditions are very different depending on whether the purification of the first or second component is being optimized. Similarities can be observed with the optimum conditions observed when the same separation is carried out in isocratic elution. The recovery yield is very high for the more retained component, moderate for the less retained one. Since the initial retention factor is much higher in gradient elution than the optimum found in isocratic elution, the optimum plate number is rather small in gradient elution. When the two solutes are convergent, very fiat gradient steepness should be used, preventing a reversal of the elution order.
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