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Starch is a highly disperse material with broad distributions of molecular sizes and geometries. Its dissolution in aqueous media is difficult to achieve and it tends to form aggregates through both inter- and intra-molecular interactions. Asymmetrical flow field-flow fractionation (AF4) is a suitable technique for the separation of such macromolecular and colloidal systems. A major advantage of AF4 is the direct correlation of translational diffusion coefficients with retention time and experimental parameters. In this article, the hydrodynamic and diffusive mobility of normal corn starch dissolved in 0.035 M KSCN was investigated by systematically varying the cross flow rates (applied forces); the translational diffusion coeffcients for normal corn starch in aqueous medium were found to range between 9.9 x 10-9 cm2/s and ~2.5 x 10-7 cm2/s with varying Fcr rates. Diffusion coefficient ranges shifted to higher diffusion co-efficient values at higher cross flow rates (applied forces). This behaviour, which may be attributed to the increased retention of very large starch molecules/particles at high Fcr rates, is further confirmed by the decrease in apparent molar mass and mass recovery values.

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Recently, we have reported studies of transport and sorption of heavy metal ions in water-saturated quartz sand columns under relatively fast water flow. In these experiments, clear indications for a fast and strong adsorption of the ions to the sediment could be found. Here we report the findings in a series of other experiments performed under static conditions. In this case, much higher concentrations of ions are adsorbed to the sand and remain immobile over time scales of more than a year. Changes in the MRI contrast observed for the sediment areas with the adsorbed ions indicate rearrangements in the distribution of the ions during the first days after administration to the sediment. EDX-studies of the ion distribution after several days indicate a spatially inhomogeneous distribution of adsorbed ions on the surface of the quartz sand. If the adsorbed ions are subjected to flow, a part of adsorbed ions moves away with the water flow. Also all ions are rapidly accessible to acid leaching.

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