pH electrode jargon buster
21 June 2016
21 June 2016
Using a pH electrode which is right for your type of samples will make sure your results are accurate and your electrode lasts the longest time possible.
With so many electrode available to choose from, how do you know where to begin? And what do all the different terms mean?
We’ve broken down the main features you might see advertised to bust through the jargon and show you how to choose the right pH electrodeRemember that no matter what type of pH electrode you use proper storage, cleaning and calibration are always required to maximise the electrode lifetime.
pH electrodes are considered consumable, you should expect to replace your electrode roughly every 6 to 12 months depending on the application.
Ag/AgCl – this is the chemical symbol for Silver / Silver Chloride. This is a type of reference electrode (see Reference)
Combination – this means the electrode contains both the pH electrode and the reference electrode. Most modern electrodes will be combination, though it is possible to still use separate pH and reference electrodes for some high accuracy laboratory work. Combination electrodes still do not include the temperature sensor.
Double Junction – the electrode has 2 junctions internally, to prevent the sample reacting with the chemicals inside the electrode. This is essential if your samples might contain protein, heavy metals or sulphides.
Epoxy – the main body of the electrode is made from Epoxy plastic resin (instead of glass)
Electrolyte – this is the liquid or gel filling inside an electrode which connects the sample to the meter and the reference element. For electrodes with a liquid electrolyte, this will slowly diffuse through the junction so the liquid level will fall over time and will need topping up. Gel electrodes use a semi-solid gel so will not require refilling. Liquid electrolyte electrodes usually offer a slightly faster Response Time.
Flat (or Flat Tip)- the tip of the electrode is a flat shape – for measuring on the surface of solids or in sticky liquids that would get stuck in the small spaces in standard electrodes. See image below.
Junction – this is the divider between the Reference electrode and the sample. Liquid Electrolyte slowly escapes through the junction in liquid filled electrodes. If the sample reacts with the electrolyte it can produce a solid which blocks the junction – using a Double Junction electrode will usually avoid this problem.
KCl – this is the chemical symbol for Potassium Chloride which is commonly used as an Electrolyte solution or as a storage solution.
Reference (or Reference Electrode) – pH measurement requires a pH electrode and a reference electrode. Usually these are combined in a Combination electrode. The reference electrode has a stable and known potential which the pH electrode reading is compared to, giving the overall result. In most standard applications it is not necessary to choose a specific reference type.
Refillable – sometimes used to describe electrodes with a liquid Electrolyte, as this will diffuse out over time and the liquid will need to be refilled.
Response Time – this is the average time taken for a stable reading to be found. Bear in mind that this will vary with the sample, condition and age of the electrode so it should not be taken as an absolute value.
Soaker bottle (aka Soaker Cap or Storage Bottle) – a small bottle which attaches to the working end of the electrode for storage. This should be filled with storage solution to ensure the electrode is kept hydrated (if it dries out it will fail and need replacing). The soaker bottle should be removed before testing or calibration, it is only used for storage.
Spear Tip – the tip of the electrode has a pointed tip for pushing into soft solids such as meat or cheese. See image above.
S7 (or S7 connector) – this is a connection type at the end of the electrode with a standard size screwthread. The S7 screwthread will connect directly to a TRUEscience cap, but may need an additional cable for other meters.
Three in one (3-in-1) – these electrodes include the pH electrode, reference electrode and temperature sensor. These types of electrode often have 2 plugs at the end of their cable, and are often specific to one manufacturer so you may not be able to use other brands.
Got any other pH measuring jargon you want us to bust? Let us know via the Contact page and we’ll be happy to help!