Polyvinyl chloride forms a hydrophobic, highly plasticized membrane, which can influence the selectivity of the sensor due to the difference in hydrophobicity of detected species but also serve as protective barrier against proteins. It was already shown that the pore size can influence the long-term stability of sensors, with smaller pores providing greater stability in blood . Significant reduction of the syringaldazine signal was observed after coating of the electrode with polyvinyl chloride. The protective layer also negatively influenced the peak separation.