The opposite effect of temperature on polyethylene glycol-based aqueous biphasic systems versus aqueous biphasic extraction chromatographic resins

Variation in operational temperatures has revealed differences in the partitioning behavior of probe solutes between the phases in aqueous biphasic systems (ABS) and the related aqueous biphasic extraction chromatographic resin (ABEC). This difference has been studied using the hydrophobic anion, 99TcO4−, as a probe and (NH4)2SO4 as the kosmotropic salt. Distribution of the hydrophobic anion 99TcO4− to the PEG-rich phase in a MePEG-5000/(NH4)2SO4 ABS increases with increasing temperature, but decreases are observed in batch uptakes of this anion to ABEC resins from (NH4)2SO4 solutions. Phase diagrams were constructed at five different temperatures from 10 to 50 °C using cloud point titration for the ABS and a correlation between the phase divergence, measured in terms of tie line length (TLL), and the temperature of the partitioning system was verified. Thermodynamic parameters (ΔH°, ΔS°, ΔG  °, ΔCp°) as a function of temperature were calculated for the various systems studied and the results imply thermodynamic differences between partitioning in ABS versus ABEC.