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Guidelines for pH Electrode Maintenance and Use
Like any piece of equipment pH electrodes have a certain life expectancy. However, with proper care and maintainence you can maximize your electrode life.
Knowing factors that influence electrode life can help you better understand and care for your electrode.
Extend the life of your pH electrode by following the steps below.
1. Hydration of the glass bulb
A very thin layer of water forms on the pH glass sensor. This layer is known as the hydrated layer. As an electrochemical sensor the hydration layer affects the voltage generated by the pH sensor.
A probe that has a hydrated layer will generate a different voltage in a pH buffer than a pH electrode without a hydrated layer. So calibrating a dry electrode will cause inaccurate readings when taking measurements as the hydration layer is formed. A dry probe needs to be hydrated by placing in storage solution before calibration. The hydrated layer takes 3-4 hours to form.
Every combination pH electrode has a junction. A junction is a barrier between the internal reference wire and the sample that is measured. The reference cell has a salt solution that leaks through the junction as part of the electrical circuit. If a probe is dry the salt will precipitate in the junction causing to be clogged. The pH readings will be erratic. A dry probe needs to have the junction hydrated to work properly.
Specially formulated to keep the glass hydrated while minimizing organic growth
3. Fill Solution Level for Refillable pH Electrodes
pH electrodes that are refillable need to have their electrolyte (salt) level checked. The probe should be filled when the level falls below ½” from the fill hole opening. Having enough fill solution ensures that the reference wire is in solution for a single junction electrode and continuity with the inner junction for a double junction electrode. A proper level also allows for adequate head pressure to force electrolyte through the junction.
4. Remove/Loosen Reference Fill Cap When in Use
In order to create head pressure the fill cap must be loosened or removed from the top of the electrode. Removing/loosening the reference fill cap allows for air to enter into the reference cell. The solution within the probe will want to flow through the junction resulting in increased stability when taking a reading.
Fill solutions for both single and double junction electrodes
Single junction electrodes use 3.5 M KCl with silver chloride
Fresh calibration solution should be used when calibrating a pH electrode. All pH measurements are based on the pH calibration solution as a reference point.
The pH calibration buffer is a water-based solution that will change over time. This is especially true for pH 10.01 buffer that will actually decrease in pH as atmospheric carbon dioxide enters the solution.
Bottles of buffer should be replaced after they have been opened for 6 months.
Never pour calibration buffer back into the bottle.
Basic, Technical, and Millesimal pH buffers
Accurate to ±0.01 pH for Basic and Technical
Accurate to ±0.002 pH for Millesimal
Technical and Millesimal buffers supplied with a Certificate of Analysis (COA)
The pH electrode should be rinsed in purified water (RO, DI, or distilled) before placing in any pH calibration buffer. This will reduce the chance of contaminating the buffer.
A best practice would be to use two beakers/containers for each calibration buffer. The process would be to rinse the pH electrode with purified water then rinse the probe in one of the beakers with the buffer then place the probe in the second beaker with buffer.
This procedure would be repeated for multiple calibration points.
For two point calibration the pH buffers used should bracket the expected pH reading. For example I expect a pH 5 reading then the pH electrode should be calibrated in pH 7 and pH 4 buffers.
Hanna offers pH buffers from pH 1.000 to 13.00
Available in a variety of sizes
Available in variety of packaging from single use packets to 1 gallon bottles
