Sensors for pH Measurement in the Laboratory and in Industrial Processes

pH Electrodes

Specialized Laboratory and In-Line Process pH Electrodes for High-Precision Analysis

A pH electrode is an analytical sensor that determines the acidity or alkalinity of a solution by measuring hydrogen-ion activity. Many industries rely on them for their high precision, accuracy, and ease of use, including pharmaceutical, chemical, food and beverage, semiconductor, water, and wastewater treatment. METTLER TOLEDO offers a wide range of pH electrodes suitable for laboratory and in-line industrial applications, ensuring exceptional quality and dependability.

Call for Quote


What are in-line pH electrodes and what types are there?

In-line pH electrodes are devices used to measure the acidity or alkalinity of a process fluid. There is one main type of in-line pH electrode on the market: the combination electrode.

Combination electrodes contain both a hydrogen-ion (H+) sensitive electrode (glass membrane or X-Chip™) and a reference electrode in a single housing. However, there are different types of pH glass membranes for electrodes, each with unique properties for specific applications.

METTLER TOLEDO offers a range of pH membrane glasses, including:

  • High alkali-resistant glass for high pH values and temperatures
  • Low-temperature glass for low temperatures and ion concentrations
  • A41 glass for steam sterilization resistance
  • Hydrofluoric acid-resistant glass for processes containing HF

Unbreakable X-Chip technology is available for InPro X1pH sensors.

There are also different types of reference systems that can be paired with the various pH glass membranes for every application. METTLER TOLEDO offers several reference systems to suit different needs, such as:

  • Pressurized liquid reference systems with Argenthal silver ion trap and ceramic diaphragms
  • Double chamber reference systems with PTFE diaphragms
  • Open junction reference systems with polymer solid electrolytes
  • Gel-filled reference systems with ceramic diaphragms

Each reference system has its own advantages and is suitable for specific applications, ensuring accurate and reliable pH measurements across a wide range of processes.

How do pH electrodes work?

A pH electrode works by measuring the difference in electric potential in mV between a glass membrane or X-Chip and the reference electrode in a solution.

The pH-sensitive section of the electrode detects the activity of hydrogen ions at its tip. The silver/silver chloride reference comes into contact with the solution through either a diaphragm or an open junction and provides a steady reference potential. The potential difference is then used to calculate the pH value using the calibration parameters of the pH sensor, either saved on the sensor itself in the case of digital ISM sensors, or on the transmitter for analog pH sensors.

What is the expected lifespan of a pH electrode?

The lifespan of an in-line pH electrode depends strongly on the conditions of the process. pH electrodes can last anywhere from a couple of days to well over a year with no degradation in performance. However, factors such as exposure to highly alkaline process conditions and extreme temperatures can shorten their lifespans.

How do I know if a pH electrode is accurate?

To determine whether the pH electrode you are using is accurate, you should test it in a standard solution. To begin, immerse your pH electrode in a pH 7.0 solution. It should take around one minute for your pH meter to display a pH value of 7.0. After that, rinse your pH electrode well and place it in a pH 4.0 buffer solution. Your pH meter should indicate a pH value of 4.0. Repeat these steps until you get an accurate reading.

If electrodes are not cleaned after use or are neglected long term, they will lose their accuracy, reducing the measurement precision of the whole system.

The accuracy of your measurements depends on a variety of factors, such as the accuracy of the calibration buffers, whether temperature compensation was used, if the electrode was the right electrode for the particular sample measured, if it had enough time to equilibrate, and whether the meter's endpoint/measuring point was correct.

Does calibration of a pH electrode ensure a precise measurement?

Yes, to ensure accurate and precise pH measurements, in-line pH electrodes require regular calibration intervals that are dependent on the process conditions. A typical two-point calibration should be performed every two weeks using pH 4.01 and pH 7.00 technical buffers from METTLER TOLEDO. The results of the calibration provide valuable information about the electrode’s health. The slope and offset values are then used to adjust the electrode for precise pH measurement until the next calibration is due.

pH electrode calibration at measurement points can be cumbersome and possibly hazardous for maintenance staff. ISM solves this issue with our ISM Core software and Plug and Measure feature.

ISM electrodes carry their own identification and calibration data on an internal microchip. This means electrodes can be calibrated in any convenient location via ISM Core. Once calibrated, an electrode can be stored until it is required. Upon connection to an ISM transmitter at the measurement point, the transmitter configures itself automatically. This Plug and Measure ability ensures fast, error-free electrode installation. ISM pH electrodes monitor their need for calibration, and the connected transmitter displays this as the Adaptive Calibration Timer (ACT).

ISM pH electrodes come factory-calibrated and can be used immediately after unpacking.

What are the advantages of digital ISM pH electrodes?

Intelligent Sensor Management (ISM™) is an innovative concept for processing analytical measurement solutions. The advantages of digital ISM pH electrodes mean that maintenance becomes predictable, failure in the process is avoided, and production uptime is increased.

ISM pH electrodes monitor their own “health” based on current and past process conditions and convert this information into easily understood predictive diagnostic tools. The Dynamic Lifetime Indicator (DLI) provides an accurate reading of how many days remain before a sensor should be replaced. The Adaptive Calibration Timer (ACT) shows the remaining days before calibration should be performed.

Through monitoring the ACT and DLI and taking preventive actions, the chances of a sensor failing in the process are eliminated. This minimizes sensor maintenance and helps to increase uptime.