Joule-heated working electrodes are used for the enhancement of electrochemical analysis. Due to heating, a temperature gradient is created near the electrode surface. The temperature pulse potentiometric method was used to perform a temperature calibration for the heated screen-printed electrode, in order to apply the desired temperature during analysis. The applied temperature of the working electrode influences the electrochemical potential of a redox couple. Open circuit potentiometric (OCP) measurements were performed with several screen-printed gold loop electrodes (AuLE), applying five heat pulses of 50 kHz AC provided by a ThermaLab AC generator. Heat pulses, potentiometric read-out and mathematical fit were conducted automatically by a new controlling software. These potentiometric temperature calibrations were performed using a 5 mM equimolar solution of the redox couple ferri/ferrocyanide in 0.1 M KCl at 20°C bulk electrolyte temperature. Potential differences, read-out automatically during each heat pulse, were used to calculate the electrode temperature using the temperature coefficient of the standard potential of the redox couple (-1.60 mV/K). The temperature calibration experiments repeated with five AuLEs were reproducible and precise, with an RSD for the temperature of 0.24%. The average margin error of OCP-calibrated temperatures was ±0.66 K at a 95% confidence level. In this work, a quick, reproducible and accurate temperature calibration was possible for disposable AuLE. We applied the new heated sensors for mercury trace detection. A mercury deposition temperature study revealed an increase in Hg stripping signal of almost 30-fold at 70°C, compared to room temperature (23°C), where heat was not applied. The heated electrodes improved the sensitivity by a factor of 10. The limit of detection for Hg(II) was found to be 9 ppb at 60°C deposition temperature, compared with 23°C measurements that resulted in 20 ppb. Further tests with tap and river water samples are underway. The ultimate goal is to avoid any sample preparation.

Mercury trace analysis using automatically temperature-calibrated heated screen-printed gold electrodes

256th National Meeting (2018)

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