At Hanna, we have over 100 pH electrodes to choose from and it can be quite a challenge to get the right one if you don’t know what you are looking for.
Here, we will cover how our electrodes are made and what to consider when you are making your choice.
There are quite a lot of variables that need to be considered and whether to go for the wireless option now with our HALO range.
These include:
- The specification of the glass membrane
- Glass membrane profile (shape)
- Junction type
- Electrode body material
All about the glass membrane
The membrane, the main sensing part of the probe, can be affected by high temperature and each electrode is given a maximum temperature level. Excessive temperatures for electrodes can have a significant impact on the electrode life. When choosing an electrode, take into consideration which one will suit your application best.
General purpose glass (GP)
Our general purposed hydrogen sensitive glass provides the greatest response over the entire pH range and can be used for a wide variety of applications.
Low temperature glass (LT)
This type of glass has a lower impedance and is suitable for samples at lower temperatures and lower conductivities.
High temperature glass (HT)
Designed for extended use at elevated temperatures where glass impedance is known to decrease, high temperature glass offer a higher resistance making it possible to obtain accurate results with excellent response times.
Hydrofluoric acid glass (HF)
Glass dissolves rapidly in Hydrofluoric acid, so we offer HF resistant glass for aggressive applications containing fluoride ions. HF glass membranes last ten times longer than standard GP glass formulations in these conditions.
Bulbs style profiles have the greater area of contact, Spear electrodes are ideal for semi-solids, creams and sauces etc. Surface electrodes are also great at small volume samples when the sample is placed on a microplate slide for example.
Glass membrane profiles
There is then the shape to consider. Again, consider what you are testing before making your choice.
Spheric profile
For general use in aqueous solutions, provides a wide surface area for liquid contact.
Conic profile
Best for slurries, emulsions, semi-solids and solids. Well suited for samples such as soil, gels, sauces, cheeses and meats.
Flat profile
Allows for direct surface pH measurement. Ideal for testing the pH of skin, leather or paper.
Dome profile
Similar to a spheric profile, the area used where a smaller profile is required in electrode construction such as in titanium bodied electrodes.
What Junction type should you choose?
When new, the junction in an electrode will be white/cream colour. As use continues, the junction will grow darker, and can indicate possible contamination where the sample enters the electrode.
Some glass electrodes have multiple junctions to help measure samples that are complex. Here are the main junctions to consider.
Porous ceramic
Most commonly used because it easily fuses with electrode glass and has a similar coefficient of expansion.
Porous PTFE
One of the most chemically resistant junctions available, it is ideal for industrial applications because of its chemical resistance and durability.
PTFE Sleeve
Ideal for samples with high amounts of solids such as slurries, sauces and wine must. The sleeve allows for high electrolyte flow and prevents clogging.
Fibre wick
Also known as a cloth junction, it is typically used in titanium bodied and gel filled electrodes. Ideal for field use, the junction’s renewable surface allows for a quick refresh when readings become unstable or erratic.
Open
Utilise a special formulation of gel electrolyte which directly contacts the sample. Offers low contact resistance coupled with a low clogging potential. These are ideal for food solids, semi-solids and emulsions.
Considering Electrode bodies
Plastic bodied probes are a favourite in applications where operatives can be a little heavy handed! The point to think about here is that if there are solids in the sample they can get stuck between the castellation and the bulb. The bulb can be easily broken when teasing lumps out of the end of the probe.
Glass body electrodes is resistant to a wide variety of chemicals, is easy to clean and transfers heat easily making it the stable of pH electrode body materials. They are ideal for a wide range of laboratory applications.
PEI body electrodes or Polyetherimide is a high performance durable plastic that offers excellent chemical resistance against aggressive chemicals. Rugged and resilient, they are ideal for environmental and industrial applications.
PVDF body electrodes or Polyvinylidene fluoride is food grade plastic that is also chemical and solvent resistant.
It is durable and easy to clean and is ideal for electrodes used in the pH measurement of food products.
Metal body electrodes - We manufacture electrodes in Stainless Steel and Titanium and both materials produce a rugged electrode ideal for use in a wide range of chemicals and harsh environmental conditions.
What is a combination pH electrode?
Previously, it was common to measure pH using two half cells separately (reference and measuring cell).
Today it is more common to use a single combined electrode which incorporates both cells as it is just so much more convenient to have a combination. A number of our electrodes also include the temperature sensor, making it much easier to use particularly in the field.
So there isn’t too much to remember when making your purchase! Just:
- Which glass type?
- Which membrane?
- Which junction?
- Which electrode body material?
Plus . . .
- Temperature range of sample
- Physical properties of the sample; flat, semi-solid, viscous, solid, emulsion etc.
- Pressure of the environment the electrode will be placed in
- Environmental conditions: lab based, field based, high humidity etc.
Using the right electrode for your application and looking after it gives you a head-start in:
✔obtaining accurate results
✔longer electrode life
✔minimising erratic readings
✔frequency of calibration
Choosing a Conductivity meter/electrode
Know how to identify the conductivity probes:
1 If you see two graphite or stainless steel pins or plates then it is a two electrode probe
2 A single probe with four rings on it is a potentiometric
3 While a conductivity probe used in industrial process equipment and has a circular loop at the end and is called an inductive, electrodeless or toroidal probe
Hanna testers with two-electrode sensors come in different models for different ranges.
If you are testing a variety of samples, a four-ring probe may be a better option for you. They are a good choice when you're working over a wide range and don't want to use multiple probes.
If you need a probe to work with process equipment, inductive conductivity probes stand up to harsher conditions. They have higher chemical resistance and are useful in industrial applications.
An important factor that you should consider when shopping for a conductivity meter is temperature. Many meters feature automatic temperature compensation to ensure that the measurement is consistent over a range of temperatures.
When your sample is not at room temperature (25°C), the conductivity reading will be different: Temperature increases = ions in the solution moving faster.
Meters with a temperature compensation feature make adjustments based on the temperature of your sample, providing a more accurate reading.
