The maximum water volume fraction absorbed by membrane based on Pt(II)- 5,10,15,20-tetra(4-methoxy-phenyl)-porphyrin (PtTMeOPP) in poly(vinyl)chloride (PVC) matrix applied on iron substrate is 0.3 % and the permeability is 7.6×10−12 m 2 s −1 . After 24 h immersion in the 0.5 M 4-morpholinoethanesulfonic acid (MES) solution of pH = 5.5, the Nyquist representation of impedance data shows diffusion into the membrane of electrolytes from the buffer solution, causing a decrease of the membrane electric resistance, but no delamination was observed for immersion longer than 48 h. Furthermore, the coating resistance is still close to ~16000 ohm.cm−2 after 25 hours. This recommends this membrane as good material in potentiometric sensors design