A novel chemical sensor with multiple all-solid-state electrodes and its application in freshwater environmental...

Freshwater quality detection is important for pollution control. Three important components of water quality are pH, ammonia and dissolved H₂S and there is an urgent need for a high-precision sensor for simultaneous and continuous measurement. In this study, all-solid-state electrodes of Eh, pH, NH₄ ⁺ and S^2- were manufactured and mounted to a wireless chemical sensor with multiple parameters. Calibration indicated that the pH electrode had a Nernst response with slope of 53.174 mV; the NH₄ ⁺ electrode had a detection limit of 10^-5 mol/L (Nernst response slope of 53.56 mV between 10^-1 to 10^-4 mol/L). Ag/Ag₂S has a detection limit of 10^-7 mol/L (Nernst response slope of 28.439 mV). The sensor was cylindrical and small with low power consumption and low storage demand to achieve continuous in-situ monitoring for long periods. The sensor was tested for 10 days in streams at Trawsgoed Dairy farm in Aberystwyth, UK. At the intensively farmed Trawsgoed, the concentration of NH₄ ⁺ in the stream rose sharply after the application of slurry to adjacent fields. Further, the stream was overhung with extensive vegetation and exhibited changes in pH, which correlated with photosynthetic activity. Measurements of S^2- were stable throughout the week. Our data demonstrate the applicability of our multiple electrode sensor.