Polyethylene glycol (PEG)-grafted aqueous biphasic extraction chromatographic (ABEC) resins have been shown to remove both mercury(II) cations (Hg2+) or perchlorate anions (ClO4-) from aqueous media under different conditions. Water destructuring (chaotropic) anions such as perchlorate (Delta G(hyd) = -214 kJ/mol) partitioned to ABEC resin in the presence of water structuring (kosmotropic) anions, with increased affinity for the resin as the kosmotropic nature of the anion increased (Cl- < SO42- < PO43-), and could be easily stripped using water. However, while the partitioning of ClO4- to the resin was possible only in the presence of a kosmotropic salt; Hg2+ was retained from the resin only in the absence of such salts (i.e., from pure water) and stripped from the resin when eluted with kosmotropic salt solutions. Here, the different mechanisms for uptake of these ions by an ABEC resin are explored.