Abstract
The pertechnetate anion quantitatively partitions to the upper polyethylene glycol (PEG)-rich phase in aqueous biphasic systems (ABS) formed by the addition of aqueous high-molecular-weight PEG solutions to aqueous water-structuring salt solutions. Most metal cations partition to the salt-rich phase in these systems. Other matrix ions, such as those that might be present in real-world waste streams, affect the distribution ratios observed for TcO4 −, however, the effects are not well understood. The halide ions F−, Cl−, Br−, I− represent a wide range of water-structuring to chaotropic ions. The heavier halide ions have distribution ratios above one and are observed to follow the order DI > DBr > DCl. These ions depress DTc. Fluoride saltsout PEG and thus partitions primarily to the salt-rich phase and fluoride increases DTc. These trends can be correlated with the ions' Gibbs free energies of hydration (ΔGhyd), a measure of their interactions with water. Based upon these results, it is possible to predict which ions will depress, elevate, or not affect DTc for a given PEG-ABS based upon the matrix ion's Δ Ghyd.
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