End-effects and band spreading in liquid column chromatography

Abstract

The band spreading process due to velocity inequalities in column extremities where an uneven flow profile settles is described by the field shape, column diameter and mobile phase velocity. An analogue simulation with a resisting network is presented; this method makes it possible to determine the flow pattern at each column extremity. A knowledge of the flow field to determine one to calculate the characteristic variance of peak broadening with a parameter λ expressing the shape of the flow field i. e., the relative magnitude of velocity inequalities. This variance is proportional to the square of the column diameter and the square of the ratio of the connecting tube and column diameters; it further depends on the permeability and thickness of porous frits in the column ends; finally, this variance depends on the mobile phase velocity; if the mobile phase velocity is low, molecular diffusion corrects the band spreading due to flow inequalities. The peak broadening resulting from end-effects can be so important that under extreme conditions the column efficiency can be reduced more than ten-fold.