I am looking for alternative methods to measure the pH of water (swimming pools, tap water, rivers,...) with (ideally) the following properties:
- Durable: no maintenance or calibration required for 5-10 years.
- Accurate: 0.1 pH or better.
- In-line measurement.
- Expected pH measurement range: 5 - 10
The 'durable' aspect rules out the traditional pH probe as it needs to be calibrated and replaced quite often.
So far most of the papers I have read use an electrochemical cell and a measurement technique such as cyclic voltammetry, square-wave voltammetry, electrochemical impedance spectroscopy,... which has the disadvantage of needing a reference electrode. A calomel electrode (which should be more durable) is not an option since it contains mercury and an AgCl electrode would also require calibration, maintenance or replacement I believe. For a working electrode they use all kinds of materials and coatings such as ITO (indium tin oxide), glassy carbon,...
I did find one commercially available product which seems to be promising: https://www.anbsensors.com/
They seem to use an entirely solid state sensor, using Nafion coated flavanone carbon composite electrodes with square wave voltammetry. They claim no calibration is required and maintenance (abrasion) every 15.000 measurements.
I also looked into ISFET's (ion sensitive field effect transistor), they also seem to have some drawbacks such as drift, still needing a reference electrode, limited availability,...
Would determining the ratio between bicarbonate ions and carbonate ions / carbonic acid be a feasible option?
In short, does anyone have any pointers or recommendations on topics or measurement techniques to research further?
Sidenote: I have a background in electronics engineering and a basic understanding of electrochemistry.
