Application of soil mechanics and the finite element method (FEM) to High Performance Liquid Chromatography (HPLC) columns

The efficiency of High Performance Liquid Chromatography columns is often reduced due to radial variations of the density or void ratio of the silica packing material. This heterogeneity is due to wall friction effects during column preparation, and although the friction reduces the column efficiency, some friction is required to stabilize the bed during the chromatography process and ensure a leak-proof seal between bed and wall. To investigate the induced heterogeneity during the compaction process, concepts from soil mechanics were used to study the column preparation process. Laboratory tests were conducted to measure the relationship between permeability and void ratio. The coefficient of friction between a typical packing material and the stainless steel column wall was determined in the laboratory, and the volumetric response was modeled with a nonlinear elastic-plastic model. The effect of wall friction and piston shape on the radial distribution of void ratio was then investigated by numerical analysis. The effect of loading rate was investigated using a coupled mechanical-seepage model. The results suggest that the homogeneity of the packed bed can be improved by reducing the effects of wall friction, and increasing the rate at which the piston compacts the column.