Hydrodynamic chromatography: packed columns, multiple detectors, and microcapillaries

Hydrodynamic chromatography (HDC) is a liquid chromatographic technique that separates analytes on the basis of their size in solution. Separation can be conducted either in an open tube or in a column packed with inert, nonporous beads. In HDC, larger analytes elute first and smaller ones later, due to preferential sampling of the streamlines of flow in the open tube or in the interstitial medium of the packed column. Because of the low shear rates experienced in HDC, coupled with the wealth of information obtained when employing a multiplicity of detection methods, the technique has experienced a resurgence in recent years in both the particle sizing and macromolecular arenas, where it can provide information on the mutual interdependence of molar mass, size, shape, and compactness. Additionally, microcapillary HDC is also gaining popularity amongst the bioanalytical community, who have employed the technique, inter alia, to separate DNA fragments over a base pair range spanning four orders in magnitude. Here, examples from the literature are used to show how HDC has been applied in each of the aforementioned areas, explaining the information that can be obtained from various detector combinations, and opining on the future of the technique.