A stochastic view on column efficiency

First, the validity of this proposed stochastic model was tested by adjusting the predicted to the observed reduced van Deemter plots of a 2.1 mm × 50 mm column packed with 2 μm BEH-C18 fully porous particles (FPPs). An excellent agreement was found for ui = 0.93uc, a result fully consistent with the FIB-SEM observation (ui = 0.95uc). Next, the model was used to measure ui = 0.94uc for 2.1 mm × 100 mm column packed with 1.6 μm Cortecs-C18 superficially porous particles (SPPs). The relative velocity bias across columns packed with SPPs is then barely smaller than that observed in columns packed with FPPs (+6% versus + 7%). uw=1.8ui is measured for a 75 μm × 1 m capillary column packed with 2 μm BEH-C18 particles. Despite this large wall-to-center velocity bias (+80%), the presence of the thin and ordered wall packing layer has no negative impact on the kinetic performance of capillary columns. Finally, the stochastic model of long-range eddy dispersion explains why analytical (2.1-4.6 mm i.d.) and capillary (<400 μm i.d.) columns can all be packed efficiently (1 3) with sub-2 μm particles and with 1 μm particles, respectively.