Evaluation of the uniformity of analytical-size chromatography columns prepared by the downward packing of particulate slurries

The axial heterogeneity of downward slurry-packed chromatography columns was evaluated. A series of columns were prepared that varied in total length from 5 to 30 cm. Each column was packed in stainless steel tubing that was sectioned to allow the column to be divided into 5-cm sections after packing. Each 5-cm section of these columns was then tested for chromatographic performance. In total, 22 such column sections were tested. The results of the study show that the consolidation of the packed bed is a very complex problem, yet systematic variations of the column performance were observed, depending on the location of the section tested from within the entire column. For example, when columns longer than 20 cm were packed, the most homogeneous and best performing section of the column was the lower midsection. Whereas for columns shorter than 20 cm in length, the best sectioned region of the bed was the lower and outlet region. In all cases, the most poorly packed region of the bed was the column inlet section, irrespective of the bed length. The phenomenon associated with this axial heterogeneity undoubtedly results from a complex interplay between wall friction, particle momentum, and the pressure pulsations resulting from the packing process.