Column-Only Band Broadening in a Porous Shell Radially Elongated Pillar Array Column

In the quest for better performing separation media for liquid chromatography, micropillar array columns have received great interest over the past years. While previous research was mainly focused around micropillar array columns (μPACs) filled with cylindrical pillars, this contribution discusses μPACs with rectangular pillars, which, for the first time, have been anodized and hence carry a mesoporous shell. We report on a series of on-chip measurements of the band broadening and flow permeability in a μPAC with very wide radially elongated pillars (3·75 μm) and with an interpillar distance (2 μm) between that of the first (2.5 μm) and second generation (1.25 μm) of cylindrical μPACs. Because of the extreme flow path tortuosity, this type of μPAC can produce very large plate numbers over a short distance. Despite the relatively large interpillar distance, we obtain H_min = 0.26 μm for a nearly unretained component (phase retention factor, k' ≈ 0.24) and H_min = 0.79 μm for a retained component with k' ≈ 3. The kinetic performance in terms of separation impedance (E_i = 19) is considerably improved compared to cylindrical pillar μPACs (E_i in range 40-50) and is in excellent agreement with the theoretical value for an open tubular channel with a rectangular cross-section (E_i = 18). This shows that rectangular μPACs can be represented as a parallel bundle of interconnected open-tubular channels.