SELECTIVE AND QUANTITATIVE PARTITIONING OF PERTECHNETATE IN POLYETHYLENE-GLYCOL BASED AQUEOUS BIPHASIC SYSTEMS

Abstract

The partitioning behavior of technetium has been investigated in polyethylene glycol (PEG)-based aqueous biphasic systems using K₃P0₄, K₂C0₃, Na₃(citrate), (NH₄) ₃(citrate), (NH₄) ₂S0₄, and NaOH as biphase-forming salts, and PEGs with average molecular weights of 1500, 2000, 3400, and 6000. Pertechnetate quantitatively partitions to the PEG-rich phase in these systems. The distribution ratios increase with increasing salt or PEG concentration used to form the aqueous biphasic systems, consistent with the increasing phase incompatibility. At a given concentration of salt and PEG, D_Tc values in the various systems increase in the order NaOH < (NH₄) ₂S0₄ < (NH₄)3(citrate) < K₂C0₃ < K₃P0₄ and PEG-1500 < PEG-2000 < PEG-3400 < PEG-6000. The distribution ratios are lower at very high or very low pH values than they are in the 3-9 pH range. Matrix ions may also influence the D_Tcvalues by affecting the aqueous biphasic system composition. Technetium can be stripped from the loaded PEG-rich phase by contact with a clean salt solution containing SnCl₂, which reduces TcO₄ to an oxy-chloro cationic species that partitions to the salt-rich phase.