Theoretical Prediction of the Ideal Support Shape of 3D-Ordered Liquid Chromatography Supports

Anticipating a future where advanced 3D printing or other microfabrication techniques will allow shape of chromatographic supports with quasi unlimited freedom, we tried to formulate an answer to the question of how this shape should ideally look like. For this purpose, permeability data and plate height curves have been generated for a wide diversity of perfectly ordered, fully porous support structures and for a broad range of zone retention factors (0 ≤ k″ ≤ 16), using the recently introduced Two-Zone Moment Analysis method. The plate height data show a strong difference between the nonpermeable, nonretentive case and the fully porous, retentive cases. Combining the plate height data with the permeability data, the kinetic plot analysis shows that, in general, the geometries with an axially invariant cross-section give lower inherent separation impedances, bringing them to within a factor of 2 of the separation speed of the open-tubular cylindrical capillary (theoretical best LC shape), at least when neglecting potential printing or fabrication inaccuracies. Accounting for the occurrence of a lower limit on the fabrication resolution, the best performing structures are those having their critical size (= shortest linear distance in either the solid or liquid zone) as close as possible to the average zone size. This is the case for the segmented parallel plate geometry, which could produce N = 50,000 theoretical plates 3 times faster than current best possible fully porous packed bed, assuming that a critical printing size of d_crit = 1 μm can be reached without inducing significant local size differences (10 times faster when d_crit = 0.5 μm can be achieved).