Ion exchanger‐based electrodes for determination of highly lipophilic physiologically active amines: Peculiarities of functioning and ways for improving analytical characteristics

New experimental data are presented demonstrating a much stronger pH dependence of the potential of electrodes with plasticized ion exchange membranes sensitive to cations of highly lipophilic physiologically active amines than would be expected from protolytic equilibrium in solution. Using an example of a vinpocetine‐sensitive electrode, the effectiveness of the dynamic diffusion model of the boundary potential for describing the effect of pH on the form of the electrode function is demonstrated. A simple equation for estimating the effect of distribution of the molecular form of amine between the solution and the membrane phases on the lower detection limit was obtained in the framework of a stationary diffusion model. It has also been shown that the selectivity of electrodes to cations of tertiary physiologically active amines relative to inorganic ions drastically depends on the basicity of the plasticizer (up to 6 orders of magnitude), and among the commercially available ones, ortho‐nitrophenyl octyl ether is the best. Besides, this plasticizer provides the lowest detection limit (1.7×10 −7 M) and the best potential reproducibility (0.06 mV) for vinpocetine‐sensitive electrode.