NEW TECHNOLOGIES FOR METAL-ION SEPARATIONS - AQUEOUS BIPHASIC EXTRACTION CHROMATOGRAPHY (ABEC) .1. UPTAKE OF PERTECHNETATE

Polyethylene glycol (PEG) based-aqueous biphasic systems (ABS) have be en adapted to a solid aqueous biphasic extraction chromatographic (ABE C) mode by grafting high molecular weight PEGs to a solid support and using high ionic strength salt solutions as mobile phases. The new res ins behave as an ABS: in the presence of high ionic strength solutions of water-structuring anions (e.g., SO42-, CO32-, OH-, etc.), chaotrop ic ions (e.g., TcO4-) are retained. Stripping is accomplished by washi ng the resins with water, thus lowering the ionic strength and no long er mimicking an ABS environment. Monomethylated PEGs (Me-PEGs) of aver age molecular weight 350, 750, 2000, and 5000 have been grafted to chl oromethylated polystyrene-1%-divinylbenzene. Quantitative uptake of tr acer-scale pertechnetare has been achieved from NaOH, (NH4)(2)SO4, K2C O3, and K3PO4 for the two higher molecular weight PEG resins, with ret ention increasing as the molecular weight of the grafted Me-PEG increa ses. No uptake is observed from water. The relationship between partit ioning of solutes in liquid/liquid ABS and retention by the ABEC resin s has been confirmed by the following observations. The conditions nec essary 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-structu ring salt increases, as the Delta G(hyd) of the water-structuring anio n becomes more negative (for a given concentration of salt solution), and as the molecular weight of the supported polymer increases. No upt ake occurs from salt solutions that do not contain a sufficient concen tration of biphase-forming salt.