EPR measurements show that sorption of copper aqua complexes from alkaline solutions by AN-31 anionite involves the formation of compounds that yield no EPR signal, most probably hydroxides. A part of the sorbed copper forms tetraamine complexes via an interaction with functional groups of the anionite. A paramagnetic probe can be used to study the state of diamagnetic metal ions in the ionite phase. Paramagnetic probe measurements show that polymeric forms of aqua complexes of Al(III), Ga(III), Pb(II), and Zn(II) exist in the anionite phase.