Enhancement of the separation efficiency through temperature control in preparative high-performance liquid chromatography columns

The flow regime in analytical and preparative HPLC columns is most commonly assumed to have the shape of an ideal plug. This is a helpful simplification for the mathematical treatment of thermodynamics and kinetics of the separation process, but does not necessarily depict the realistic conditions in the separation column. In reality there are different factors causing a deviation from the plug flow pattern in a chromatographic column. The homogeneity of the chromatographic bed determines its permeability, The temperature in the column has an impact on the local viscosity of the eluent. The permeability of the chromatographic bed and the viscosity influence the local velocity of the eluent. The distribution system of the column inlet affects the shape of the eluting band profile. The problem of an even distribution of the injected mixture over the entire diameter of the column increases with increasing column dimensions. The present paper reports some results about the influence of the eluent temperature on the flow regime and the shape of the eluting peaks. It reports clearly how to control the shape of band profiles and how to compensate for a distributional lack by means of the eluent temperature. Pictures taken from eluting dye bands resulting from different chromatographic conditions serve as a clear basis for the effect of the discussed observations. (C) 1998 Elsevier Science B.V.