The fate of eight metal ions, Co(II), Cr(III), Cr(VI), Cu(II), Fe(III), Mn(II), Mo(VI) and Ni(II), introduced as minor components in the well-known aqueous biphasic system PEG-400/Na2SO4/H2O was investigated at T = 25°C and as a function of the increasing PEG-400 amount in the system. Among this list, the six cations Co(II), Cr(III), Cu(II), Fe(III), Mn(II) and Ni(II) tend to be excluded from the upper PEG-rich phase as the PEG amount is increased, a behavior which is similar to that of Na(I), a major component of the system and the binodal curve (shape and position) is not modified by their presence. By contrast, the two oxoanions Cr(VI) and Mo(VI) accumulate in the upper PEG-rich phase (up to ca. 100%) as PEG amount in the system is increased, which is similar to a traditional extraction phenomenon, assimilating PEG to the (organic) extracting phase. The extraction mechanism, ascribed to the PEG crown-ether open chain properties, is supported by experiments where the PEG structure is slightly modified.