This work summarizes the electrochemical response of a salicylic acid-based carbon electrode for use as a novel solid-state reference electrode in a redox-based pH sensor. This novel reference produces a pH insensitive response over a range of pH 3–10 in solutions with low buffer concentrations, different compositions, conductivities, and ionic strengths is produced. The pH of the local environment is shown to be determined by the chemistry and the electrochemical response of the redox active species on the surface of the electrode; the local pH can be controlled by the electropolymerized salicylic acid moieties due to the acid concentration on the surface, avoiding any perturbation in environmental pH and leading to a stable novel reference system. Sensitivities of −7.1 mV/pH unit, −2.4 mV/pH unit, −0.2 mV/pH unit, and 2.5 mV/pH units were obtained for different food medias, hydroponic solution, seawater, and cell-culture media, respectively, confirming its ability to control the local pH of the electrode. This reference system is paired with a new pH sensing element based on electropolymerized flavanone to provide a calibration free, pH sensitive sensor to effectively and accurately measure the pH of various media with high viscosity, low conductivity, low/high buffer concentration or cell-culture environment, presenting a maximum error of +/−0.03 pH units.
This work summarizes the electrochemical response of flavanone carbon composite electrodes in comparison with Nafion ® -coated flavanone carbon composite electrodes, for use as voltammetric pH sensors in both buffered and low-buffered media. Square wave voltammetric measurements suggest the peak potential achieved from the electrochemical polymerization after the electron-proton oxidation responds with accuracy to buffered pH solutions for both coated and non-coated electrodes, with a potential shift of 55.1 mV and 54.6 mV per pH unit respectively. However, a considerable improvement in stability, accuracy and sensitivity is provided by the proton-transfer Nafion ® layer in CO 2 bubbled sea water. Furthermore, Nafion ® -coated flavanone carbon composite electrodes predicted a pH of 8.04 for the commercial seawater, which is in excellent agreement with the measured pH 8.05 value.
Abstract. An electrochemical based, all solid-state, calibration-free pH sensor is presented. The sensor is targeted for monitoring the pH of ocean and estuarine environments covering a salinity range from 10–35 ppt without the need for additional salinity measurements. The sensor performance is demonstrated in both laboratory and field conditions. The field tests were conducted in an estuarine environment close to Oban in Scotland where the sensor was deployed for a period of three days. The sensor was validated against a sampled solution and tested alongside a glass pH sensor. The data highlighted the efficiency of the sensor to monitor the tidal variations of pH in the estuarine environment.
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