Improvement of Analytical Characteristic of Calcium Selective Electrode with Conducting Polymer Contact. The Role of Conducting Polymer Spontaneous Charge Transfer Processes and Their Galvanostatic Compensation

In this report processes affecting the analytical characteristic of all‐solid‐state, conducting polymer–polypyrrole based cation selective sensors are discussed on an example of a Ca‐electrode. It is shown that conditioning of the obtained electrode is coupled with transducer spontaneous discharge leading to accumulation of calcium cations in the polymer phase. As an ultimate result of this process, the sensor detection limit is close to 10−5 M, similarly as for traditional internal solution electrodes. The compensation of polypyrrole spontaneous charge transfer process over conditioning, by anodic galvanostatic polarization, prevents Ca2+ accumulation and results (in subsequent open circuit calibration) in linear responses within the activities range from 0.1 M to 10−10 M. In dilute solution, due to limited accessibility of cations in the solution and relatively high amount of cations present in the transducer phase, the spontaneous charging process of conducting polymer determines the accessible detection limit. It is also shown that in this case the linear range of responses can be extended to reach significantly lower activities under conditions of polarized electrode potentiometry, applying a cathodic current. The outstanding stability of the open circuit equilibrated all‐solid‐state sensor is attributed to accumulation of primary ions in the sensor transducer phase during conditioning.