Publication
Microchannels hosting spatially-periodic supports for the stationary phase have drawn intense attention in Liquid Cromatography (LC) research in the last two decades, with second-generation μPACs (micro-pillar array columns) setting the current limit of separation efficiency both in terms of plate height and flow resistance. Inspired by recent theoretical and experimental results, suggesting that an increased rate of transversal mixing in the mobile phase can significantly reduce the dispersion bandwidth of the analytes, we investigate and numerically predict the separation performance of a capillary LC column hosting a periodic alternate sequence of helicoidal baffles arranged in a Kenics Mixer (KM) configuration. The comparison of the KM-LC column performance with that of packed, random-monolithic, and μPAC columns, carried out by matching the capillary diameter of the KM to the size of the flow-through pores of the other geometries, shows a potential further enhancement of LC efficiency, with a minimal plate height reduced by a factor 3 for an unretained solute, and by a factor 2 for a solute with retention factor k=2 with respect to the best performing columns reported so far. This improved performance is achieved without compromising in terms of pressure losses, as evidenced by the significant reduction in separation impedance observed across all practically relevant flow velocities when compared to other LC technologies. We propose that the performance enhancement of the KM geometry results from a combination of factors: the minimal nature of the helicoidal surface, which influences the rate of viscous dissipation, and the chaotic advection mechanism in the mobile phase, which mitigates the increase in plate height as eluent velocity increases. Specifically, we find that in the KM geometry, the Cm-term of Golay's equation accounting for the mobile phase contribution to axial dispersion scales slower than linearly with the reduced velocity of the eluent, ur, as Cmurα, with α strictly lower than unity.