Solid-Contact Potentiometric Cell with Symmetry

Abstract

By its nature, a traditional potentiometric cell composed of an Ag/AgCl-based reference electrode and a solid-contact indicating electrode is not symmetric. This results in undesirable potential drifts in response to a common perturbation such as a temperature change of the sample. We propose here an approach to restore symmetry by constructing a cell with two identical solid-contact ISEs used as reference and indicating electrodes. In this arrangement, the reference electrode is immersed in a compartment containing a constant background of an ion of interest, while the indicating electrode is directly immersed in the sample solution. This approach was successfully demonstrated for a cell composed of nitrate-selective electrodes with the hydrophobic derivative of poly(3,4-ethylenedioxythiophene) as a transducer layer. In particular, the symmetric setup is shown to lower by 4−5 times the observed potential drift resulting from temperature changes between +25 and +5 °C.

Temperature Self-Calibration of Always-On, Field-Deployed Ion-Selective Electrodes Based on Differential Voltage Measurement

“…In this section, we first validate the theory of temperature self-calibration through existing literature data and our laboratory experiment results involving arbitrary heating of the analyte solution and measurement of the corresponding pH and nitrate concentration. Once the theory is validated in the laboratory, we demonstrate the effectiveness of the approach through the field deployment of the nitrate sensors.…”

“…(e) Pairwise voltage difference and (f) self-temperature of nitrate sensors. (g) Reported voltage of Nitrate-SE #1 and #2 with respect to the Ag/AgCl reference electrode in the 1 mM nitrate solution . (h) Voltage difference of two ISEs and (i) self-temperature along with the reported temperature.…”

“…Figure shows the experimental results of the temperature-corrected activity of pH and nitrate sensors in the temperature self-calibration method that is considered in our laboratory experiment and reported in ref (Figure ). It is clear from Figure a and eq that, even at a constant concentration, voltage varies due to the temperature variation.…”

“…Measured activity before temperature correction (Raw) and after temperature correction ( T -corrected) with pH and nitrate sensors used in our laboratory experiment and reported in ref . (a) pH vs time and (b) absolute error of the measured pH relative to the true pH.…”

“…The crosstalk between electrical signals of the temperature sensor and ISE may further reduce the accuracy. To lower the voltage drift due to temperature variation, a symmetric setup comprising of two identical SC ISEs, one as a reference and other as an indicating electrode, has been recently proposed . The improvement is significant, but the temperature variability is not completely eliminated.…”