Theoretical Assessment of the Potential Kinetic Advantage of Spiky Particle Columns for Liquid Chromatography

We report on a computational study to gain insights into the potential advantage of spiky particles in packed bed columns for liquid chromatography. Using the recently adopted Two-Zone Moment Analysis method, a comprehensive set of band broadening data has been generated over an exhaustive range of particle/spike combinations and shapes, velocities, diffusion coefficients, and retention factors. It has been found, under the strict limitation of the presumed perfect ordering of the particles, that the spikes can be expected to lead to a drastic decrease of the beds’ flow resistance φ (up to a factor of 10 and more) compared to the no-spike case. This is due to the increase in external porosity ε caused by the spikes keeping the particles further away from each other. The presence of the spikes, however, also leads to an increased band broadening, albeit that this increase is much more modest than the decrease in flow resistance. This leads to the overall situation that spiky particles, if they could be produced with sufficient mechanical strength and size uniformity, could offer a way to significantly lower the minimal separation impedance Emin (=hmin2.φ) of packed-bed HPLC columns. In the hypothetical, perfectly ordered particle packings considered in the present study, Emin dropped with a factor ranging between 3 and 12, depending on the length of the spikes (longest spikes give the lowest impedance). However, to truly benefit from these low separation impedances in the plate number range of main practical interest, the spiky particles would require ultra-small particle diameters, down to and even well below 1 μm.