An Investigation into Capillary Hydrodynamic Chromatography

Now fifteen years ago, Small and co‐workers [1, 2], introduced Hydrodynamic Chromatography (HDC) as a simple method for the sizing of submicron particles. The particles are fractionated when flowing through a packed column of uniform impermeable beads and emerge in order of decreasing diameter. Noel et al. [4] and Mullins and Orr [3] reported a variant of the technique using a long open capillary tube which has been called Capillary Hydrodynamic Chromatography (CHDC). Recently Brough et al. [5] were able to expand the size range of CHDC down to particle diameters of 0.07 μm and showed that the technique is also able to achieve fractionation in organic solvents. In an attempt to obtain the same particle size analysis range with CHDC as with the recently commercialised HDC (Micromeritics), we investigated the CHDC performance in very small capillaries (0.1 and 0.15 mm). The emphasis of the study has been led on the nature and the concentration of the eluent composition. Indeed an effective reduction in capillary diameter can be obtained if one uses a commercial block copolymer as eluent material. Adsorption of the block copolymer both on the capillary wall and the particles gives rise to a sterical barrier which reduces further the effective capillary diameter and enhances the resolution of the column towards smaller particle sizes. In our view CHDC represents more possibilities in analysing real particle systems, i. e. dispersions with relatively high polymer or polyelectrolyte concentrations. For such systems classical HDC results mostly in the clogging of the column. A series of dispersions and emulsions in concentrated gelatine have been analysed and the P. S. are compared with the results obtained by LCS.