pH measurement in hygienic applications

Whether for quality control, optimising efficiency, or contamination identification, pH monitoring and control of final product or raw materials play a crucial role in the food and beverage industry. With that in mind, what are the technologies available for a reliable online measurement?

Glass pH electrodes, which are commonly used in lab routines, have gone through several enhancements since their creation. This has allowed for their use under high pressures, high temperatures and exposure to different chemical components.

Although hygienic models exist, the possibility of ‘glass breakage’ limits the use of glass electrodes in food and beverage applications due to internal good manufacturing practices, despite the use of filters and adequate personnel.

The ceramic diaphragm used in electrodes for hygienic applications has pores with diameters smaller than 0.1 µm, making sure no microorganisms enter the electrode.

If you get goosebumps just by hearing the word ‘glass’ in your process — don’t worry, there are other pH measurement alternatives that can easily overcome this limitation, such as ISFET electrodes.

The ISFET electrode

Do you want a real-time pH measurement of your process without having to worry about glass breakage risks?

The ISFET (Ion Selective Field Effect Transistor) electrode uses a pH sensitive semiconductor attached to a highly resistant structure made of PEEK (polyether ether ketone). This ensures its physical integrity against process-induced mechanical and thermal shocks. To ensure its suitability in food and beverage applications, the polymer used in the sensor construction does not have any sort of chemical additives in its composition, complying with FDA (Food & Drug Administration) requirements for food contact applications with maximum operational safety.

PEEK has excellent mechanical, electrical and chemical compatibility properties, allowing its use in applications that range from the manufacturing of medical prosthesis to electrical insulators used in the aerospace industry.

Just like glass pH probes, ISFET electrodes have been through countless performance improvements over time. A well-known limitation for these sensors was the exposure to high temperature, high alkalinity (pH >12) applications which contributed to a drastic reduction in lifetime. The new generation of electrodes have additional resources in terms of chip protection and composition that allow operation even in CIP (cleaning-in-place) intensive applications.

Regardless of the technology used for pH measurement, one thing we need to keep in mind is that these sensors are consumables due to different chemical interactions that happen internally and require periodic maintenance and replacement.

To overcome some of these challenges, the use of retractable assemblies is beneficial in terms of maintenance and performance improvement. Some of the benefits include the ‘hot tap’ removal of the pH from pressurised tanks and pipes as well as ‘by-pass’ cleaning. In this case, the pH probe can be retracted from under stressful process conditions and cleaned at lower temperatures, increasing the lifetime of the probes.

“What if I don’t have a retractable assembly or resources to take care of the pH probe maintenance?”
In that case, there’s a third technology available for pH measurement called Enamel Electrodes.

The enamel electrode

This option is not well known in the market but can perform miracles in terms of maintenance and durability. The enamel electrode uses a robust ceramic structure composed of several enamel layers (like the one we have with our teeth) that are sensitive to pH variation.

Due to the material composition and the techniques used in the manufacturing, these electrodes can handle direct exposure to CIP and SIP with negligible drifts in measurement. This increases the calibration intervals in some cases — up to one year, while dismissing the need for retractable assemblies.

Another advantage enamel electrodes have in comparison to other pH technologies is the larger measuring area (around 15 cm²). This is superior to conventional pH electrodes (1 cm²), ensuring highly accurate measurements even in high viscosity applications. This option can minimise your OPEX.

The use of inline pH monitoring today is uncommon due to uncertainties that range from contamination risks, to lack of manpower to manage the maintenance. However, as discussed, different approaches and resources are available for even the most demanding applications. Real-time measurement with inline sensors is a powerful resource for decision-making, allowing early identification of non-conformities and improving food safety and process efficiency.

For more information, visit: https://www.au.endress.com/en/field-instruments-overview/liquid-analysis-product-overview/pH-sensors-transmitters.