Selecting the appropriate pH probe for your application requires a basic understanding of probe construction. Please read the "pH electrode design" page of this site.
The type of probe or electrode features you will choose all depend on your application, on what media you will measure. This page will comment the different parts of a pH electrode and provide the information you need to select the appropriate electrode for your application.
The pH probe body is available either with a glass or
plastic (epoxy or polymer) body. Traditionally, pH electrodes have been
constructed entirely of glass. However, today's plastics allow pH
electrodes to be constructed with sturdy and chemically resistant epoxy
or polymer bodies.
The glass body electrode is most often used in laboratory applications and is the best choice for solutions containing proteins and organics or solvents, which might attack a polymer body. The glass body is still to be preferred for highly corrosive materials and high temperature applications. A glass body is also easier to clean in comparison to a plastic body..
A plastic body electrode is a good choice for applications where rough handling and breakage are a major problem. They usually have a gel or solid polymer electrolyte.
A pH electrode is available in different lengths. A common electrode length is 120 mm.
The length of your electrode is probably of more interest for online pH measurement applications than for laboratory use.
The glass membrane or the probe tip is made of pH sensitive glass. And as already described there are different pH membrane glass types available.
The glass membrane needs to be taken care of and knowing how to restore the hydrated glass layer is important.
An important parameter is the temperature. Make sure the temperature range of your application matches the temperature range of the chosen pH electrode.
Highly acid or alkaline media
At very low (< pH 1) or high pH values (>pH 12) your electrode needs a special glass membrane to minimize the acid and alkaline errors.
Different shapes of the pH probe tip offer you a choice between optimal connection with the measured sample and the ruggedness of the pH sensor.
common problem related to pH electrodes are the contamination and
clogging of the reference junction, resulting in slow, drifty and noisy
measurements. Take the time to understand what type of reference junction your measurement requires.
potassium chloride electrolyte (KCl) is the most frequently used
reference electrolyte, it is not applicable to all applications. Learn
more about different types of reference electrolytes.
The most common reference element is the silver/silver chloride (Ag/AgCl) element. It has a couple of advantages. However, it will cause problems for many applications. Make sure you know when to select the silver chloride reference element.
Since temperature has a strong influence on your pH measurement your chosen pH probe should have a temperature sensor embedded in the body to ensure that temperature compensation is carried out automatically.
The lifetime of your pH electrode is heavily dependent on the application, and how you maintain it. A well-maintained pH electrode will function for 6 to 12 months in most typical applications.
Tough applications which expose your electrode for high temperatures, high process pressure, or aggressive media, will reduce the lifetime of your pH electrode. Even you have picked the most appropriate electrode. However, if you pick the wrong electrode type for your application you can destroy your pH electrode in hours or minutes......
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