pH Electrode Design

A pH electrode is available in a number of different shapes and dimensions to fit a wide range of applications. However, not only the geometrical dimensions differ between pH sensors, even the glass composition and the shape of the pH sensitive membrane can vary, as well as the electrolyte and the junction or diaphragm of the reference electrode.

Just to clarify, when we say a pH electrode we mean, in most cases, a glass pH combination electrode. There are also non-glass electrodes available on the market.

Let's look at the different parts of a pH glass electrode:

pH electrode

Sensor body

There are two common choices for body material: glass and and some form of plastic. The glass body is ideally suited for most routine pH measurements for high temperature and ease of cleaning. The plastic body is a good choice for applications where rough handling and breakage are a major problem.

Electrodes are available in different lengths. A common length is 120 mm.

Glass membrane

The glass membrane is the pH sensitive part of the electrode. And as the pH sensor is designed for many different applications, so are there also different pH membrane glass types available.

Shape of membrane

Not only the type of the glass membrane is important, also the shape of the probe tip plays an important role for your pH measurement.

Reference junction

To get a stable and accurate pH measurement, you need to make sure the reference electrode is working properly. The critical connection point is the reference junction. It can either be an open junction or a porous diaphragm.

Reference electrolyte

The most common reference electrolyte is a potassium chloride electrolyte (KCl). However, a KCl-solution is not applicable to all applications.

Reference element

The main function of the reference element is to electrically connect the pH meter to the reference electrolyte.

Temperature response time

temperature response time

An important parameter to consider at the electrode design development is the temperature response time of the pH sensor.

A fast temperature change of the measured media will cause the pH value to fluctuate until the temperature of the inner and the external reference element of the electrode and the media are equal. To facilitate a quick and uniform temperature distribution in the electrode it is a clear advantage to place the reference elements symmetrically in the sensor.

Temperature sensor

Since pH sensors have a pH temperature relationship, most electrodes have a temperature sensor embedded in the body.

Accurate pH measurements

To be able to perform accurate pH testing you need to have a basic understanding of the design of a pH electrode. After all, your chosen electrode will determine the performance of your pH measurement.

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Solid polymer 
I was wondering what type of 'solid polymer' should be used in reference sensors. And where could one obtain this material?

Calibration of the temperature sensor 
Hello, I'm finding very informative, so thank you! I've never given the topic much though before, but I have to define procedures for …

pH Electrode body 
Even the two common choices for body material are glass and plastic, there are other alternatives, as for example stainless steel and titanium. "Plastic" …

pH junction, diameter of diaphram Not rated yet
Hi, Thanks for a great site. I have 2 pH reference junctions, one with a small diameter permeable diaphram and one with an obviously larger diameter …

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pH Electrode design

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