pH Electrodes Types And Uses
Many measuring instruments have an Electrode as the main component. And the manuals of the instruments say “maintain the Electrode well for accurate readings.” Well, that’s because an Electrode is a sensitive component. Since the topic of this article is “pH Electrode types and uses,” I will focus more in the pH Electrode. The earliest pH Electrodes just had a glass bulb, strong electrolyte, a half-cell, and an Ag wire. Anyway, it’s safe to say that the working principle of the Electrodes hasn’t changed a lot. But the modern technology has created new designs such as gel-filled, combination, double junction, calomel junctions, ion selective, solid state, and Epoxy body Electrodes.
The most common type available today is the combination type. These Electrodes have a glass hydrogen ion electrode and a reference electrode. Anyway, you can’t see the two separate electrodes as both are in one housing.
Combination Electrode working principle: This type measures the potential difference between the two sides. It has to be a closed circuit to measure the potential difference, so the internal solution within the electrode and the external solution close the circuit. The external solution is the one that is being measured with the pH meter. When you immerse the pH meter Probe in the solution, the positive charge H+ ions will be detected by the glass bulb as a millivoltage. The internal solution then picks up the millivoltage signal and passes it to the electronics through the cable.
So, why do you need a reference Electrode? Well, it’s there for a reason. The electrolyte in the reference Electrode generates a constant millivoltage and transfer it to the Ag/AgCl wire. The signal from the Ag/AgCl wire is considered a “control.” Ultimately, the pH meter measures the internal electrode and reference electrode difference, and display in on the LCD screen. As mentioned, this type is the most common choice today. If you read articles about pH meters, most of the articles explain only the combination Electrode. That’s because it’s the most common type.
OK, I will explain a bit of pH and the pH meter too. pH is the “potential of Hydrogen.” pH scale runs from 0 to 14. Well, in school-days; you must have done the litmus paper test, don’t you? Below 7 is acidic, 7 is neutral, and above 7 alkalines. Superacids have pH values above 14 or below 0. Measuring pH is an essential in many industries today. For example, the food industry, cleaning industry, water treating, and much more.
For industrial purposes, a litmus paper is not a reliable method (because you need accurate and easy readings.) A pH meter is an electronic device, so very accurate and straightforward to use. Every pH meter has an Electrode as explained so far.
A general pH Electrode will last from 1-2 years if maintained properly. Choosing the wrong electrode would give you inaccurate readings also will shorten the life of the electrode. If you don’t maintain it properly, the service life can be shortened to just a few months. Modern pH meters come as fixed electrodes and replaceable electrodes. The top disadvantage of buying a fixed-type – you will have to get rid of the meter if the electrode stops functioning. Anyway, these meters are cheaper than the replaceable ones.