(163e) Characterization of Liquid Adsorption Columns by Computed Tomography (Ct)

The efficiency of liquid adsorption and especially chromatographic columns strongly depends on a homogeneous structure of the packing, e.g. an evenly distributed interstitial void fraction. Evidences that the structure of the packed bed is not necessarily homogeneous can be found in the literature. The inhomogeneities of the packing can either be a consequence of the packing process or are caused by the operation of the column. In either case they lead to maldistributions of the mobile phase flow and a deterioration of the separation efficiency.

In order to investigate local column properties, computed tomography (CT) as a non-destructive measurement technique was employed. Using this technique, the chromatographic column is exposed to x ray beams from different directions. The attenuation of the beams after passing the column is measured. The attenuation data which depend on the material examined allow for the reconstruction of a two dimensional image of the column cross section. From these images the information about the local column properties can be extracted. For frontal analysis experiments, the progress of the fronts can be monitored and viewed inside the columns.

The experiments were carried out using a reversed phase material (C18) packed into glass columns of different diameters. Water and methanol as well as solutions of potassium iodide were applied as mobile phases. Due to its relatively high atomic mass, iodine strongly attenuates the x-ray beams thereby enhancing the image contrast. The use of a reversed phase system shall contribute to the suppression of interactions in between polar groups on the surface of the adsorbents and the ionic tracer.

The results of this work shall contribute to gain a better understanding of the packing structure of chromatographic columns and the influence of an uneven packing on the performance of the separation process. Long term goal is the implementation of the experimental results into spatially more dimensional models of chromatography.