CONTINUOUS SPLIT FRACTIONATION BASED ON A DIFFUSION MECHANISM

We describe here the theoretical and experimental basis of continuous SPLITT fractionation in a diffusion mode, in which the transport region becomes a thin liquid diffusion barrier (a virtual membrane) dividing the sample input region from the collection region. With flow rates properly adjusted, low molecular weight components rapidly penetrate this barrier, leading to a substantial accumulation in the collection region. At the same time, only a small fraction of the higher molecular weight components will traverse this barrier because of more sluggish diffusion. Consequently, in a very short time (typically, a few tens of seconds) a substantial enrichment of the high molecular component can be achieved, although at the expense of some sample dilution. Preliminary experiments using several proteins and sodium benzoate are described that show excellent agreement with theory. Gravitational convection is shown to be generally negligible but can be induced by the presence of a densifier such as sucrose.