All-solid-state ion selective electrodes (ASS-ISE) are promising sensors for environmental and clinical applications. They benefit from lack of liquid phase (no risk of leakage), relatively low cost, possibility of miniaturization and wide linear response range. These electrodes consist of electronic conductor (electrode support), ion-to-electron transducer (usually conducting polymer) and polymeric ion-selective membrane, usually poly(vinyl chloride) (Fig. 1). In this work glassy carbon (electrode support), conductivity polymer: polypyrrole and K⁺-selective membrane with K⁺-ionophore (valinomycin) was used.

Fig. 1. Structure of ASS-ISE K⁺

Under open circuit potential conditions, the detection limit of this sensor is close to 10^-6 or even 10^-7M, depending on kind of lipophilic salt present in the membrane. Because the polymer is covered by a cation-exchanging membrane, K⁺ ion spontaneously flow from the conducting polymer to the diluted sample solution. This effect leads to higher K⁺ concentration next to membrane surface and thus to detection limit. In this work cathodic galvanostatic polarisation was used to compensate this flow and to lower the detection limit to 10^-8M (Fig. 2).

Fig. 2. Potentiometric characteristics of one of the studied electrodes under open cuircut conditions (squares) and for galvanostatically polarized electrode (triangles), I=10 nA.

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