Detailed kinetic performance analysis of micromachined radially elongated pillar array columns for liquid chromatography

The individual factors that determine the kinetic performance (B- and C-term band broadening and bed permeability Kv) of radially elongated pillar (REP) columns are studied. To this end, columns with REPs having 4 different aspect ratios (AR = 9, 12, 15, 20) were characterized experimentally and by means of numerical simulations. A tortuosity and retention based plate height equation was established, enabling a good global fit for all studied conditions. The B-term plate height contribution appears to decrease with a factor equaling the square of the flow path tortuosity τ. Going from AR = 12 to AR = 20 (τ = 5.7 and τ = 9.0 respectively), this resulted in a shift in plate height expressed in axial coordinates from Hmin = 0.42 μm to Hmin = 0.25 for non-retained conditions and from H = 0.77 μm to H = 0.57 μm for a component with k = 1.0. The obtained parameters were combined to predict optimal time-efficiency combinations for all possible channel lengths. This revealed an efficiency limit of N = 107 plates for a non-retained component and N = 7-8 × 106 for k = 1 for a channel with an AR = 20, corresponding to a channel length of 2.5 m and a void time of 2.4 h.