Visualization of viscous fingering in chromatographic columns

A 17 mm I.D. glass column, packed with YMC-15 (spherical C-18 silica, 30 mu m particles) as the stationary phase and used with carbon tetrachloride as the mobile phase provided a suitable system for the visual observation of viscous fingering inside the packed bed, after the cylindrical lens effect had been canceled. Such a system appears nearly transparent due to the close matching of the refractive indices of the mobile and the stationary phases. The profiles of the bands obtained upon the injection of a flat pulses of a solvent of different refractive index were readily observed. On-column detection using a 35 mm photographic camera was employed for the direct recording of band profiles. A toluene UV marker was used to record subsequent elution profiles via UV detection. The influence of the sample viscosity, the mobile phase flow-rate, and the injection volume on the extent of viscous fingering and band broadening were studied. Viscous fingering was shown to increase with increasing difference between the viscosity of the sample injected and the mobile phase. Viscous fingers were more clearly delineated at higher flow-rates, but band distortion was observed even at flow-rates as low as 0.2 ml min(-1). The degree of band distortion was observed to increase with increasing volume injected. Finally, viscous fingering was found to be a reversible process, as previously reported. (C) 1998 Elsevier Science B.V All rights reserved.