pH Electrode Selection Guide
With hundreds of uses, selecting the right pH electrode can be a challenge. Use this helpful selection guide to be sure you are ordering the appropriate electrode for your application.
Gel Filled vs. Refillable Electrodes
Gel-filled electrodes are convenient and easier to maintain. However, the liquid-filled electrode will provide a faster response. Users can also replace the fill solution to optimize performance.
Glass vs. Epoxy Body Electrodes
Glass body electrodes will typically be able to withstand higher temperatures. The glass design offers better sealing, fusing glass to glass instead of relying on adhesives. The epoxy body is susceptible to breakage.
pH electrodes are hand-blown by experienced craftsmen and can be modified to provide a semi-dome for increased ruggedness, a spear tip for soft penetration or even a flat surface. The glass formulation can provide increased range.
To achieve accurate results, the reference electrode must allow electrolyte solution to flow into the sample. Depending on the size and material of the junction, this flow rate can be increased or kept to a minimum. Faster flow produces stable readings faster but results in greater service requirements or premature electrode failure.
The leading cause of electrode failure is reference contamination. The most popular electrodes use a silver chloride (AgCl) reference solution that can react with heavy metals, sulfides, and organics. If your application has any of these contaminants present, be sure to select either a double-junction or calomel electrode. The double-junction electrode uses a second internal reference junction, restricting the AgCl solution to the upper chamber where it is isolated from the sample. The calomel electrode replaces the AgCl with HgCl.
Thermo Scientific Orion
The type of available electrodes, the desired electrode features and the compatibility of the electrode with the sample are all determining factors in selecting the right pH electrode. pH electrodes are available with a glass or epoxy body and a variety of electrode body styles, fill types, references, junctions, and connectors that suit your application. Other factors to consider when selecting a pH electrode include:
The reference junction should provide a stable and reproducible reading under a wide variety of sample conditions. Electrodes with a Sure-Flow reference junction can be used in a variety of samples, including difficult samples such as cheese, yogurt, and viscous material.
Electrode Filling Solution
The electrode filling solution should not interfere with electrode measurements. Electrodes with a double junction reference prevent silver ions from coming in contact with the sample, which is key when measuring samples that contain proteins or sulfides. Refillable ROSS™ Ultra and ROSS™ electrodes do not contain any silver.
The filling solution should flow freely with no fouling or clogging of the junction by the sample. The Sure-Flow reference junction improves the electrode performance by allowing a constant flow of filling solution into the sample. AquaPro pH electrodes incorporate a high-performance polymer that isolates the silver internal reference from the sample. These low-maintenance pH electrodes offer a rapid response due to their open junction design, even in viscous samples.
For further assistance, please call Nelson-Jamesons lab product specialists and request the pH Measurement & Troubleshooting Guide.