February 23, 2024

Analytical Selection Guide for pH Electrode

Use this reference to determine which electrode parts and styles will perform nicely for the solutions you want to measure.

Electrode Components

Usually, pH electrodes are made in pairs. An electrode has two primary parts: a detecting half-cell and a standard half-cell to test pH and the half-cell components must be used simultaneously. The sensing half-cell of the electrode accountable for measuring is the sensing half-cell or the positive end of the circuit.

This part of the electrode often incorporates a pH-sensitive membrane. Meanwhile, the reference half-cell offers a consistent reference voltage required for pH and orp measurement; consider the circuit’s opposing end. Cole-pH Parmer’s electrodes are usually combination electrodes. They combine the reference and sensing half cells into one probe.

Cole-Parmer still provides the older sensing and reference half-cells, although they are less common. The optimal solution will vary on the samples being measured. In these cases, orp sensors and orp measurements are utilized. The sections that follow cover the various electrode types and their significant distinctions.

  1. Refillable or Sealed Electrodes

Sealed electrodes are excellent for most applications. They are also more cost-effective. The electrode must be replaced if the interior fills liquid levels are too low (or dries up). That’s why this may not last as long as refillable electrodes.

Meanwhile, in the case of refillable electrodes, a port at the electrode’s top allows it to be replenished when the internal fill solution runs out. In many cases, this can considerably extend the electrode’s life. Refillable electrodes allow individuals to replace contaminated filling solutions.

  1. Epoxy or Glass

Epoxy electrodes are more robust, cheaper, and suited for anticipated severe handling. Most epoxy shell electrodes have the highest temperature limit of 176oF (80oC).

On the other hand, glass body electrodes can tolerate temperatures up to 230oF (100-110oC) and are resistant to highly corrosive chemicals or solvents. Glass electrode bodies are also easy to clean.

  1. Single Junction or Double Junction

The most typical ceramic connectors are single or double. Individual electrodes are suited for general use and cleaner liquid purposes. They should not be used with specimens with proteins or other biological materials.

While most reference cells use an H-permeable glass connection, PTFE reference cells are also obtainable. Electrodes with PTFE connections work better with viscous liquids or particles that block glass junctions. This includes gauging oils, acrylics, pastes, and dyes.

Featured Applications for Specialized Electrode Junctions

  • Wick Junction Electrodes – mostly made from fiber optical bundles, glass fibers, and/or Dacron. It can be for aqueous samples in body electrodes of epoxy through orp sensors.
  • Open Pore Electrodes – can provide more junction and make the junction stable by raising the flow.
  • Ceramic Junction Electrodes – made of wooden plug, porous ceramic, or porous PTFE. It is commonly found in regular labs.
  • Sure-Flow Electrodes – recommended for dirty or viscous samples. This electrode prevents getting clogged through a flushable feature.

Reference Type Electrodes

Silver (Ag)/Silver Chloride (ACI)

This is the most used type of inner element because it is applicable in most applications with a temp limit of 176�F. You can also consider a thermo scientific electrode as an alternative. It features iodine or iodide in the internal reference.

Temperature Measurement / Compensation

In every pH solution, it is essential to have an orp measurement for the temperature to specify the right electrode to use. Mostly all meters come with manual or automated temperature correction. A manual temperature compensation user must input the material’s condition manually.

With ATC, you have two probing choices: to use a temperature probe separate from the pH electrode; or to consider the model of the meter when choosing the ATC probe connection type. Using a second temperature probe allows your meter to support a broader range of pH electrodes.

The other alternative is to use a pH electrode through only an ATC element. This electrode is also known as an all-in-one electrode. They are easier to use since just one probe penetrates the sample. Since these orp sensors have both pH and ATC electrodes, they usually have two connections.

Connection Variants

  • DIN Connector – the common type of electrode connection mainly for ATC probes.
  • BNC – universal type of electrode connection
  • US Standard – the traditional kind of connection that is rarely used.
  • Pin tip – has been replaced by paired electrodes but is still used.

In case you’re looking for an ATC electrode as an alternative for pH electrode, here are some options:

  • 4-pin
  • 8-pin DIN
  • Mini-DIN
  • Cinch
  • Phono jack
  • RCW plug

Specialty Electrodes

  • Narrow Electrodes
  • Standard Electrodes
  • Semi-micro Electrodes
  • Flat surface Electrodes
  • Spear Tip Electrodes
  • Rugged Bulb Electrodes
  • Antimony Electrodes

Selection Guide for Electrodes with Specified Applications

  • Pharmaceutical = ROSS electrode/ double junction
  • Low Ionic Samples = flushable styles
  • Hydrofluoric Acid = HF Electrodes
  • Biological Samples = ROSS electrode/ double junction
  • Drinking Water = Single Junction with AgCI/ Ag
  • Distilled Water and Boiler Feed Water = Flushable Styles