New technologies for metal ion separations: Aqueous biphasic extraction chromatography (ABEC) .1. Uptake of pertechnetate

Polyethylene glycol (PEG) based-aqueous biphasic systems (ABS) have been adapted to a solid aqueous biphasic extraction chromatographic (ABEC) mode by grafting high molecular weight PEGs to a solid support and using high ionic strength salt solutions as mobile phases. The new resins behave as an ABS: in the presence of high ionic strength solutions of water-structuring anions (e.g., SO42-, CO32-, OH-, etc.), chaotropic ions (e.g., TcO4-) are retained. Stripping is accomplished by washing the resins with water, thus lowering the ionic strength and no longer mimicking an ABS environment. Monomethylated PEGs (Me-PEGs) of average molecular weight 350, 750, 2000, and 5000 have been grafted to chloromethylated polystyrene-1%-divinylbenzene. Quantitative uptake of tracer-scale pertechnetare has been achieved from NaOH, (NH4)(2)SO4, K2CO3, and K3PO4 for the two higher molecular weight PEG resins, with retention increasing as the molecular weight of the grafted Me-PEG increases. No uptake is observed from water. The relationship between partitioning of solutes in liquid/liquid ABS and retention by the ABEC resins has been confirmed by the following observations. The conditions necessary for ABS extraction are necessary for ABEC uptake and the trends in partitioning behavior observed for ABS are also observed for ABEC. Resin uptake of TcO4- increases as the concentration of water-structuring salt increases, as the Delta G(hyd) of the water-structuring anion becomes more negative (for a given concentration of salt solution), and as the molecular weight of the supported polymer increases. No uptake occurs from salt solutions that do not contain a sufficient concentration of biphase-forming salt.