Picking the correct pH electrode for your application is essential to achieving accurate measurements. With more than 100 pH electrode types in our range at Hanna Instruments UK, choosing the best option for your specific purpose can be a challenge without expert advice.
In this article, we cover the key factors and differences between our electrode types, from standard glass pH electrodes to specialist stainless steel electrodes, to help you make the right choice.
If you need additional support, get in touch with us directly via email or on the phone at 01525 850 855.
What variables are there in electrodes?
There are four key variables in electrodes that differ depending on the purpose and requirements of measurement. These include:
- Glass membrane specification
- Glass membrane profile
- Junction type
- Electrode body material
Glass membrane specification
The glass membrane is the sensing part of the probe, providing information to the meter that is converted into an accurate on-screen pH reading. This membrane can be affected by high or low temperatures and corrosive materials.
The impedance range of glass membranes provides a clear idea of which electrode is suited for which application.
The primary types of glass membrane include:
General purpose glass
General purpose glass, or GP glass, is a versatile hydrogen sensitive glass that provides the most significant response for measurements. Many Hanna Instruments pH meters use GP glass for applications where higher temperatures or corrosive materials aren’t a factor, between 0-60°C.
Low temperature glass
Low temperature glass, or LT glass, has a lower impedance that is suited to cooler temperatures and conductivities. LT glass provides a viable solution for accurate measurement of frozen and refrigerated samples..
High temperature glass
High temperature glass, or HT glass, is specifically designed for elevated temperatures. Samples such as heated substances or cooking food can impact glass impedance. Choosing an electrode with HT glass provides higher resistance for accurate readings above 35°C.
Hydrofluoric acid glass
Hydrofluoric acid glass, or HF glass, has greater resistance to corrosive hydrofluoric acid. A resistant glass membrane lasts up to ten times longer than a standard GP glass membrane when testing pH in hydrofluoric acid samples. HF glass has a high alkaline error, making this option best-suited for a pH range of 2-10 pH.
Glass membrane profile
The profile of the glass membrane is the shape of the tip of the electrode. Different profiles are suited to different applications, with variations to allow for accurate pH measurements in a variety of liquid and solid samples. The Hanna Instruments pH range includes the following electrode profiles:
Spheric profile
Glass membranes with a rounded tip, ideal for use in aqueous conditions. The rounded shape of the spheric profile provides optimal contact across the widest possible surface area, for an accurate pH reading when testing liquids.
Conic profile
Glass membranes with a spear-like tip are a suitable solution for slurries, emulsions, semi-solids and solids where an electrode can be submerged within the sample. Soil, cheeses, sauces, meats and gels are ideal samples for a conic glass electrode.
Flat profile
Glass membranes with a flat head provide accurate pH measurements on direct-surface materials, such as solids where the electrode cannot be submerged into the sample. Flat profile electrodes are a popular choice for paper, leather or skin.
Dome profile
Glass membranes that have a non-glass outer construction, such as a titanium or stainless steel body, have a dome profile instead of a spheric profile. The applications for the dome profile are similar to spherical electrodes, with compromise for the rugged requirements of the pH meter in hard-wearing environments.
Junction type
The junction within a pH electrode creates electrical contact between the sample and the reference system within the electrode. The junction within a fresh pH electrode is typically a white or cream colour, which darkens over time with use, indicating possible contamination where the sample enters the electrode.
In some cases, pH electrodes may contain multiple junctions to allow for accurate measurement of complex samples. The best junction type for measuring pH will depend on several factors, including the type of material you’d like to measure and how durable you need your pH meter to be.
The primary types of junction we offer for pH electrodes include:
Porous ceramic
Porous ceramic is the most commonly used option for junctions. This material easily fuses with electrode glass and has a similar expansion coefficient, providing stability and longevity for pH electrodes.
Porous PTFE
Porous Polytetrafluoroethylene or PTFE is a chemically resistant junction and is used across numerous industries, including water treatment. This junction is an ideal option for pH meters used in industrial applications due to its resistance and durability.
PTFE Sleeve
PTFE sleeve junctions are an optimal choice for the measurement of pH in samples with high amounts of solids, such as wine must, sauces and slurries. The use of a sleeve allows for high electrolyte flow, with a design that prevents clogging caused by solids floating in liquid samples.
Fibre wick
Fibre wick junctions are also known as cloth junctions. This replaceable junction has a renewable surface that makes it ideal for field use, allowing for on-site refreshment when readings become less stable. Fibre wick junctions are typically combined with titanium, gel-filled pH electrodes.
Open
While other junctions have a frit - porous glass that allows ionic transport into the electrode - an open junction utilises a Viscolene gel that directly comes into contact with the sample. Low contact resistance and low clogging potential makes an open junction a good choice for emulsions, semi-solids and solids, such as food.
Electrode body material
The body of electrodes varies depending on their application and purpose. The options available in our pH electrode range include:
Glass body
Glass body electrodes are typically used in laboratory environments. The easy-to-clean nature of glass and resistance to a wide range of chemicals makes this option a good choice for benchtop pH meters and for testing in controlled environments.
PEI body
PEI or polyetherimide body electrodes are created from a high-performance, high-durability plastic. This plastic is resistant against aggressive and corrosive chemicals, making a PEI electrode suitable for a range of environmental and industrial applications.
PVDF body
PVDF or polyvinylidene body electrodes are made from food-grade plastic, providing a hard-wearing solution for measuring the pH of food products. PVDF electrodes are also chemical and solvent resistant, offering a versatile solution for day-to-day measurements in many industries.
Metal body
Stainless steel or titanium pH electrode bodies are rugged and practical for a range of on-site environments. Metal body electrodes are commonly used for measuring pH in harsh conditions across a range of different chemical compositions.
What is a combined electrode?
Combined electrodes offer an alternative to testing pH with separate half cells for reference and measuring. A combined pH electrode contains both cells in one, usually with the addition of a temperature sensor for accurate monitoring in a range of environments.
Our range at Hanna includes combined pH electrodes with temperature measurement for convenience in testing on-site or in a laboratory.
Buy pH electrodes from Hanna Instruments UK
As a world leader in pH testing equipment, Hanna Instruments UK is the ideal choice for reliable, accurate pH testing.
We stock a wide range of versatile and innovative electrodes, from food-safe plastic pH electrodes to heavy-duty stainless steel pH electrodes. Browse the full range online now.
If you’re unsure which pH meter or pH electrode combination is best suited to your needs, get in contact with our experts today via email or call us on 01525 850 855.
We can provide advice and specialist guidance to ensure you have the right solution for your pH testing requirements.
