pH Probe / ORP (Redox) Probe

1. What's the lifetime of a pH probe?

The expected lifetime of a correctly used and maintained pH probe is around one to three years. Some factors such as high temperature and measuring at extreme pH values contribute to a reduction of the lifetime even for probes that have been well maintained and properly stored. When a meter starts performing poorly, it may be possible to regenerate the pH-sensitive glass membrane and restore the electrode to its previous level of performance.

2. How do you select the correct pH probe?

For optimal pH measurement it is crucial to choose the right pH probe for each application. The most important sample criteria are: chemical composition, homogeneity, temperature, process pressure, pH range and container size (length and width restrictions). The choice of sensor becomes of particular importance for non-aqueous, low conductivity, protein-rich and viscous samples where general purpose glass electrodes are subject to various sources of error. The response time and accuracy of an electrode is dependent on a number of factors. Measurements at extreme pH values and temperatures, or low conductivity may take longer than those of aqueous solutions at room temperature with a neutral pH value.

3. How should you maintain/clean a probe?

Regular maintenance is very important for prolonging the lifetime of any pH probe. Probes with liquid electrolyte need the electrolyte to be topped-up when the level threatens to become lower than the level of the sample solution. This maintenance prevents a reflux of the sample into the probe. The complete reference electrolyte should also be regularly changed, approximately once a month. This ensures that the electrolyte is fresh and that no crystallization occurs due to evaporation from the open filling port during measurement. It is important not to get any bubbles on the inside of the probe, especially near the junction. If this happens the measurements will be unstable. To get rid of any bubbles, gently shake the probe in a vertical motion as with a fever thermometer.

To clean the probe, rinse it with deionized water after each measurement but never wipe it with a tissue. The surface of the paper tissue can scratch and damage the pH-sensitive glass membrane, removing the gel-layer and creating an electrostatic charge on the electrode. This electrostatic charge causes the measured signal to become very unstable. Special cleaning procedures may be necessary after contamination with certain samples.