The morphological structures of monolithic and particulate columns are radially heterogeneous [1]. Both the preparation of cylindrical silica monolithic columns and the slurry packing of fine silica particles into cylindrical stainless steel tubes generate velocity biases of the eluent across the column diameter. Parallel segmented flow chromatography (PSFC) was recently proposed to minimize the impact of these trans-column velocity biases on column efficiency [2]. The principle is simple: the whole eluent stream is not sent directly to the detector but a specially designed endfittings splits the eluent stream into its central region, sent to the detector, and a wall region that is discarded.

In this presentation, the effect of PSFC on the reduced height equivalent to a theoretical plate of small molecules is measured for short 4.6 x 30 mm columns and for different retention factors. The contributions of the reduced longitudinal diffusion, the solid-liquid mass transfer resistance, and the eddy diffusion to the column HETP were measured for two different columns packed with the same particles: one being standard, the second equipped with the special PSFC split flow endfitting. Two different packing materials were considered: fully porous 3.0 µm Hypurity-C₁₈ and core-shell 2.6 µm Accucore-C₁₈ particles. The effects of the column length (3 to 10 cm) and the particle size (3 and 5 µm) on the column efficiency were also calculated for a highly diffusive molecule (naphthalene) and for a bulkier, slowly-diffusing protein (insulin). Experimental and theoretical results are interpreted with particular concern for the transverse dispersion coefficient across the bed and the corresponding standard deviation of the radial excursion distance of molecules at the column outlet.

[1] Baur, J.; Kristensen, E. and Wightman, R. Anal. Chem. 60 (1988) 2334.

[2] Camenzulli, M.; Ritchie, H. J.; Ladine, J. R.; Shalliker, R. J. Chromatogr. A 1232 (2012) 47.