This paper discusses the problem of rigorous thermodynamic description of ionic systems in terms of ions as system constituents. This description can be based on die use of either electrochemical potentials (ECP) as a whole (without their division into chemical and electrical constituents), or twin chemical potentials (TCP) concept (introduced by the author) as thermodynamic driving forces of mass-transfer processes in ionic systems, including ion exchange. The main advantages of the approach proposed in comparison with traditional description of ionic systems is demonstrated and discussed.