A pH sensor determines the alkalinity or acidity of a solution. METTLER TOLEDO offers a broad portfolio of pH sensors for various industries, such as pharmaceutical, chemical, food and beverage, energy, and semiconductor, as well as for water and wastewater treatment. Whether you need a pH sensor in the laboratory or for in-line use, we have suitable sensors that meet all your application requirements.
Laboratory pH sensors, from routine to highly-specialized models, provide accurate readings for a wide range of lab and field applications. Read more
In-line pH sensors provide real-time, precise measurements of pH in a wide range of industrial processes environments. Read more
For optimal pH measurements, the right pH sensor is paramount. The most important sample criteria to be considered are:
For certain samples, choosing the right pH sensor is particularly important. If the fluid is non-aqueous, low conductivity, protein-rich, or viscous, general purpose pH sensors are prone to measurement errors.
The response time and accuracy of a pH sensor is dependent on a number of factors. Measurements at extreme pH values and temperatures, or in low conductivity samples may take longer than those of aqueous solutions at room temperature with a neutral pH and high conductivity.
Sensor readings must be fast, accurate, and reproducible. High-quality materials in combination with trusted technologies such as the particular reference system optimize our pH sensors to meet the requirements of your applications.
Not only do our pH sensors ensure high performance, but a correct pairing of materials and technologies makes them more durable and extends their working lifetime. We offer special shaft materials that ensure a long work life, even in harsh environments.
With our Intelligent Sensor Management (ISM) technology, pH sensors store their own calibration data and are automatically recognized when installed. Our in-line pH sensors even provide advanced diagnostics that predict when sensor maintenance or replacement will be required.
Since 1948, METTLER TOLEDO has amassed a deep expertise in providing high-quality solutions for use in the laboratory and the field. METTLER TOLEDO had its first success with the combined glass pH electrode invented by Dr. Ingold. His innovative design simplifies the way the world measures pH to this day.
At METTLER TOLEDO we uphold the tradition of Swiss craftsmanship in the production of our pH sensors and other analytical instruments, and now combine it with digital technology. See in this video how we produce our Intelligent Sensor Management (ISM) pH sensors at our manufacturing facility in Urdorf, Switzerland.
A pH sensor, also called probe or electrode, is an important tool that allows a user to determine the alkalinity or acidity of a solution. The glass membrane at the end is sensitive to H+ ions. Additionally, many of our pH sensors also offer a redox measurement.
The outside of the glass membrane forms a gel layer when it encounters an aqueous solution. A similar gel layer is also formed on the inner side of the glass membrane, since the sensor is filled with an aqueous electrolyte solution. The H+ ions in and around the gel layer can either diffuse into or out of this layer, depending on the pH value. Thus, the H+ ion concentration of the solution is measured. If the solution is alkaline, H+ ions diffuse out of the layer and a negative charge is established on the outer side of the membrane. Since the glass electrode has an internal buffer with a constant pH value, the potential on the inner surface of the membrane remains constant during the measurement. The pH sensor potential is therefore the difference between the inner and outer charge of the membrane.
The purpose of the reference sensor is to provide a defined stable reference potential against which the potential of the pH sensor will be measured. To be able to do this the reference sensor needs to be made of a glass that is not sensitive to the H+ ions in the solution. It must also be open to the sample environment into which it is dipped. To achieve this, an opening or junction is made in the shaft of the reference sensor through which the inner solution or reference electrolyte can flow out into the sample. The reference sensor and pH sensor (half-cell) must be in the same solution for correct measurements.
There are several reference systems available. These include silver/silver chloride, iodine/iodide and mercury/calomel systems, as well as some adaptations. However, the silver/silver chloride system is almost always used in modern pH measurements. The potential of this reference system is defined by the reference electrolyte and the silver/silver chloride reference element. It is important that the reference electrolyte has a high ion concentration, which results in low electrical resistance.
In the combined sensors the pH sensor (glass sensor) and the reference sensor are constructed in the form of two concentric tubes/chambers. The pH electrode envelops the reference electrode they are interconnected to each other via a ceramic junction. These two electrodes, although combined, function separately. The only difference is the ease of handling one sensor, instead of two.
One can also house a temperature sensor in the same body as the pH and reference elements. This allows temperature-compensated measurements to be made. Such electrodes are called 3-in-1 electrodes.
All user manuals provide the necessary information about short- and long-term pH sensor storage.
When using and storing a pH sensor as recommended, the expected lifetime is 1-to-3 years. However, a number of factors can decrease the lifetime of a pH sensor. One of them is its use for measuring hot or very alkaline samples. Other factors may be mechanical damage resulting from incorrect storage. Also, if the storage solution is allowed to dry or leaks out due to storage at high temperatures, freezing or other causes, the life of the probe may be reduced significantly.
The slope and offset of calibration are good indicators of the quality of a pH sensor. When these values surpass certain limits the pH electrode can be regarded as used up. The lower and upper limits for the slope are 85% and 105% and for the offset -35 mV and 35 mV. In addition, please note that an unstable signal or a very long response time in the pH calibration solution indicates an advanced deterioration of a pH sensor. These phenomena are often associated with irregular slopes and offsets.
Some of our in-line digital sensors also offer predictive diagnostics that indicate when a sensor must be replaced.