Methodology of quantitative comparison of practically achievable kinetic performance of differently structured liquid...

Previously introduced structural quality factor (q_max) of LC column is a measure of its potential kinetic performance - the larger is q_max the proportionally larger is peak capacity (n_c) of isothermal and gradient analysis with the same analysis time (t_anal) and pressure (Δp). However, the best practically achievable column performance depends not only on q_max, but is limited by the narrowest practically achievable widths of the flow-through channels in the column internal support structure. These widths can be represented by the smallest practically achievable column permeability (K_min). Large K_min might result in unnecessarily high n_c in prohibitively long t_anal. Structure-independent methodology of evaluation of these effects on a column performance limits and relevant equations are developed. The best performance (the shortest t_anal at a given n_c) is achieved when a column operates at its highest acceptable Δp (Δp_max) even if (for reducing t_anal) the column has to operate under non-optimal conditions. To demonstrate the methodology, three column types with substantially different q_max - the solid-core particle columns (SCPCs), q_max=0.4; the pillar-array columns (PACs), q_max=0.65, inter-pillar distance 1.25 µm; and the porous-layer open-tubular columns (PLOTCs), q_max=0.97, 4.6 µm ID - were compared. It is shown that, because practically available K_min of SCPCs is much smaller than that in evaluated PLOTCs or PACs, the latter two cannot outperform contemporary SCPCs with d_p≤4μm in applications with practically acceptable t_anal, although SCPCs have the lowest q_max. Factors affecting K_min, and the effect of Δp_max on a column performance limit were also evaluated and discussed.