Fluorimetric Readout of Ion Selective Electrode Signals Operating under Chronopotentiometric Conditions

The applicability of emission readout of ion-selective electrodes, containing fluorimetrically active polyoctylthiophene in the membrane, operating under chronopotentiometric mode was studied. The electrochemical and optical signals were collected in the same experiment and compared. In both modes a change in recorded signal: potential or emission in time was observed while a constant current was applied to the sensor. The recorded signals (chronopotentiometric, fluoro-chronopotentiometric curves and calculated transition times) were dependent on the concentration of potassium ions. The transition times calculated from electrochemical signals were linearly dependent on the concentration of potassium ions in solution within the range: 0.1–0.7 mM. Optically read transition times were also linearly dependent on concentration within the same range, however, they were shorter than those recorded electrochemically. This difference is attributed to various effects represented by the transition time: concentration increase of reduced form of the conducting polymer in the optical mode or depletion of potassium ions close to the membrane surface, in the electrochemical mode.