On the relation between surface area and partitioning of particulates in two-polymer aqueous phase systems

Partitioning in dextran-poly(ethylene glycol) aqueous two-phase systems is an established method for the separation of biomaterials. Size and surface properties are generally regarded as parameters which contribute to the determination of the materials' partition coefficients, K. While molecular weight or surface area can be one of the determinants of the K value of biomaterials in the size range of macromolecules to very small particulates (e.g. some viruses), partitioning liposomes of identical surface properties and different but distinct sizes indicate that surface areas greater than about 0.2 μm² do not affect the K value obtained. Analysis of available partitioning data of much larger particulates (i.e. cells) reveals that surface properties per unit area outweigh surface area per se in determining the K value in non-charge-sensitive, charge-sensitive and biospecific affinity phase systems.