3 - Structures

In potentiometric sensors, the potential difference between the reference electrode and the working electrode is measured without polarizing the electrochemical cell, that is, very small current is allowed. In that case the equilibrium electrode potential difference can be monitored, which is given by the Nernst-Nicolsky-Eisenman equation.

Amperometry is a method of electrochemical analysis in which the signal of interest is a current that is linearly dependent upon the concentration of the analyte. As the chemical species approach the working (or sensing) electrode, electrons are transferred from the analyte to the working electrode or to the analyte from the electrode. The direction of flow of electrons depends upon the properties of the analyte and can be controlled by the electric potential applied to the working electrode.

Voltammetric measurements where the whole potential-current diagrams are used for the analysis. Any reaction at the electrode surface can usually be detected as a current superimposed to the base current due to double-layer charging. Thus, in these voltammograms, current peaks can be observed. The peak potential values can be used for qualitative analysis, and the height of the peaks is a function of analyte concentration.

Conductimetric sensors are based on the measurement of electrolyte conductivity, which varies when the cell is exposed to different environments. The sensing effect is based on the change of the number of mobile charge carriers in the electrolyte. If the electrodes are prevented from polarization, the electrolyte shows ohmic behavior.