A method for producing highly sensitive potentiometric sensors by coating of electrically conductive electrodes with an electroconductive polymer, which method comprises the steps of: (a) preparing an aqueous solution for electrochemical polymerisation comprising monomeric units of the electroconductive polymer at a concentration in the range of 0.002-0.05M; and a supporting electrolyte, which also serves as a doping agent, at a concentration in the range of 0.0001-0.005M; (b) assembling an electrochemical polymerisation cell comprising the solution for electrochemical polymerisation, an auxiliary electrode, one or more working electrodes to be coated with electroconductive polymer, and optionally a reference electrode; and (c) coating the one or more working electrodes with a polymer film by the electrochemical synthesis of polymer from the electrochemical polymerisation solution using at least one of the following electrochemical regimes: (i) applying a cyclic voltage in the range -0.2 - +2.0 V vs Ag/AgCl reference electrode between the one or more working electrodes to be coated and the auxiliary electrode; (ii) applying a constant current in the single or multiple current steps with given current density in a range 0.01 - 1 mA/cm 2 between the one or more working electrodes to be coated and auxiliary electrode for defined period of time such that final quantity of electricity passed through working electrode(s) will lie in a range 10 - 250 mC/cm 2; (iii) applying a constant potential in a single or multiple potential steps at the range 0 - 3 V between the working electrodes to be coated and a reference electrode for defined period of time such that final quantity of electricity passed through the one or more working electrodes will lie in a range 10 - 250 mC/cm 2; (a) preparing an aqueous solution for electrochemical polymerisation comprising monomeric units of the electroconductive polymer at a concentration in the range of 0.002-0.05M; and a supporting electrolyte, which also serves as a doping agent, at a concentration in the range of 0.0001-0.005M; (b) assembling an electrochemical polymerisation cell comprising the solution for electrochemical polymerisation, an auxiliary electrode, one or more working electrodes to be coated with electroconductive polymer, and optionally a reference electrode; and (c) coating the one or more working electrodes with a polymer film by the electrochemical synthesis of polymer from the electrochemical polymerisation solution using at least one of the following electrochemical regimes: (i) applying a cyclic voltage in the range -0.2 - +2.0 V vs Ag/AgCl reference electrode between the one or more working electrodes to be coated and the auxiliary electrode; (ii) applying a constant current in the single or multiple current steps with given current density in a range 0.01 - 1 mA/cm 2 between the one or more working electrodes to be coated and auxiliary electrode for defined period of time such that final quantity of electricity passed through working electrode(s) will lie in a range 10 - 250 mC/cm 2; (iii) applying a constant potential in a single or multiple potential steps at the range 0 - 3 V between the working electrodes to be coated and a reference electrode for defined period of time such that final quantity of electricity passed through the one or more working electrodes will lie in a range 10 - 250 mC/cm 2; (i) applying a cyclic voltage in the range -0.2 - +2.0 V vs Ag/AgCl reference electrode between the one or more working electrodes to be coated and the auxiliary electrode; (ii) applying a constant current in the single or multiple current steps with given current density in a range 0.01 - 1 mA/cm 2 between the one or more working electrodes to be coated and auxiliary electrode for defined period of time such that final quantity of electricity passed through working electrode(s) will lie in a range 10 - 250 mC/cm 2; (iii) applying a constant potential in a single or multiple potential steps at the range 0 - 3 V between the working electrodes to be coated and a reference electrode for defined period of time such that final quantity of electricity passed through the one or more working electrodes will lie in a range 10 - 250 mC/cm 2;