Preparative separation of multi-component mixtures using stationary phase gradients

Solvent gradients have been widely applied in analytical and preparative chromatography to enhance selectivity and improve productivity. Recently, an alternative concept using solid phase gradients was introduced in analytical chromatography [Nyiredy, Szucs, Szepesy, Chromatographia 63 (2006) 3; Nyiredy, Szucs, Szepesy, J. Chromatogr. A 1157 (2007) 122]. This concept is based on connecting columns filled with different stationary phases in series, applying a constant mobile phase composition. With the availability of column connecting devices with low dead volumes [K. Bischoff, S. Nyiredy, Z. Szücs, Elements for separating substances by distributing between a stationary and a mobile phase, and method for the production of a separating device. WO/2006/125564; PCT/EP2006/004744, 2006.], the concept can be easily implemented. The application of sequentially connected columns with different properties introduces new degrees of freedom like the type, number, relative lengths and positions of individual segments. In this study, an attempt is made to analyze if such stationary phase gradients could be exploited favorably in preparative chromatography for separating multi-component mixtures. A theoretical study is carried out for a connection of two different types of column segments based on numerical solutions of the equilibrium dispersive model assuming specific adsorption isotherm parameters for each segment. The influence of relative segment lengths and the order of the arrangement are evaluated with respect to the performance of separating intermediately eluting components from multi-component mixtures.