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Home Product Solutions pH Sensors
Home Product Solutions pH Sensors

pH Sensors

Laboratory & Process Analytical pH Sensors

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.

Which pH Sensor Do You Need?

Whether you need a laboratory pH system or an in-line process sensor, use the tools below to help you find the right match for your application.

pH Lab Configurator

Designed for laboratory pH measurement, the pH Lab Configurator helps you build a complete system. Answer a few questions about your application and find the right sensor, calibration buffers, and accessories for your needs.

Start the Configurator

pH Sensor Finder

Designed for in-line pH measurements, the pH Sensor Finder helps you identify the right in-line sensor for your process. Answer a few questions about your application conditions to get a matched sensor recommendation.

Start the Finder

Find Your In-Line pH Sensor

Find Your In-Line pH Sensor

Quickly find the ideal in-line pH sensor for your process with our sensor finder tool.

Start finder
Find your pH Measurement System

Find your pH Measurement System

Rely on our pH Lab Configurator to conveniently configure your complete system, including sensors, solutions, and accessories.

Start Configurator
pH Sensors

Laboratory pH Sensors

Laboratory pH sensors, from routine to highly-specialized models, provide accurate readings for a wide range of lab and field applications.

pH Sensors

In-Line pH Sensors

In-line pH sensors provide real-time, precise measurements of pH in a wide range of industrial processes environments.

pH Sensors

Get Trustworthy Results

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.

pH Sensors

Sensors Built to Last

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.

pH Sensors

Extremely Convenient

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.

pH Sensors

A Long Tradition of Precision

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.



How pH Sensors Are Made

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.

What is a pH sensor?

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.

How does a pH sensor work?

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.

Why is a reference sensor needed while measuring pH using a pH sensor?

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.

Which reference sensor is used when measuring pH?

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.

What are combined pH sensors?

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.

What is the correct way to store pH sensors?

All user manuals provide the necessary information about short- and long-term pH sensor storage.

  • Always: In a reference electrolyte for both short- and long-term storage. This allows immediate use of pH sensor when needed, and ensures a short response time.
  • Sometimes: In buffer pH 4 and 7 between measurements to keep the membrane hydrated.
  • Never: Use deionized water as this will deplete the ion-rich reference electrolyte. Also, do not store the electrode dry as this will damage the membrane, causing the pH sensor to have a longer response time. When stored dry for long periods, many pH sensors must be reactivated by soaking for several hours before installation in order to get the optimal measuring results. If these measures are not sufficient, the sensor may be made functional by treating it with a special reactivation solution followed by subsequent conditioning in the reference electrolyte.
     

What is the normal lifetime of a pH sensor?

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.

How can I detect when a pH sensor must be replaced?

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.

What is the difference between analog and digital pH sensors?

Analog pH sensors transmit a continuous mV signal to a separate transmitter or meter, which applies the calibration parameters and calculates the pH value. They are compatible with a wide range of standard transmitters and are a reliable choice for straightforward process applications.

Digital pH sensors, such as those equipped with METTLER TOLEDO's Diagnosable, Efficient, and Sustainable (DES) technology, process the signal on the sensor itself and store calibration data, usage history, and diagnostic information on an internal microchip. This enables features such as Plug and Measure installation and predictive diagnostics, which are not available with analog sensors.

Digital DES sensors require a compatible meter and Signal Bridge. The detachable Signal Bridge transmits calibration, diagnostic, and measurement data for superior user guidance and measurement efficiency to enhance cross-compatibility, reduce setup time, and promote sustainability.

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