Different methods for inducing open-circuit cationic sensitivity of the conducting polymer (CP) films doped with Metal Complexing Ligands (MCL) are presented. Selected MCLs have the R-(MCG-H)(p)(SO3H)(n), structure and contain bulky organic group (R), "n" sulphonate groups responsible for CP doping and "p" metal complexing groups (-MCG-H) responsible for formation of the complexes with a narrow group of cations. MCLs molecules introduced to CP layer as bulky doping anions are immobilized inside CP layer and preserve their chemical properties known from water chemistry. Similarly, as ionophores, they can form complexes inside CF membrane with selected cations only. It was shown that formation of the complex inside the polymer layer is necessary for inducing preferred open-circuit sensitivity of the CP membrane. Various, efficient methods of the CP-MCL film sensitization towards calcium, magnesium as well as copper, cadmium, lead or zinc cations are presented. (C) 2014 Elsevier Ltd. All rights reserved.