If you measure the pH of solutions on a regular basis, you would know it is quite a tedious task. You have to stand there and adjust the pH of the buffer, add acid or alkali drop by drop till you get the right pH. While pH-ing can be boring, it is essential that the right equipment is used so that you get accurate results the first time around rather than having to repeat the tests constantly. In this article we will learn about how to care for the pH electrodes and importance of calibration.
The glass pH electrodes measure H concentration relative to their reference half-cells, because of which they must be calibrated regularly in order to ensure accurate and repeatable measurements. Use pH calibration buffers that include solutions standardised against NIST-certified pH references for calibrating meters with resolution up to 0.001 pH.
Calibration against one pH reference buffer or one-point calibration, can ensure accurate pH measurement. However, you will get the most reliable results by getting two-point or even three-point calibrations. Your pH system includes calibration buffers for a range of pH values. Make regular calibration a priority.
Most of the pH electrodes are shipped with their electrodes moist. Therefore, before using the electrodes for the first time, you must ‘condition’ them. There are three steps to do so:
Step 1: Remove the protective cap or rubber boot from the bottom of the sensor and rinse the electrode with distilled or deionised water.
Step 2: Place the electrode in a beaker containing one of the liquids that are listed below, in order of ionic ability, to condition the electrode. Soak the electrode for 20 minutes.
- 3.8 M or 4.0 M KCl
- 4.0 pH buffer
- 7.0 pH buffer
Once the conditioning is done, rinse the electrode with distilled or deionised water. Remember to never condition a pH electrode in distilled or deionised water for a long time as prolonged exposure to pure water damages the special glass membrane. After conditioning, the electrodes are ready for instrument calibration and to measure pH.
Cleaning and Handling
Leaving the electrodes out to dry may cause dust to settle on them or crystallised remnants of the liquid it was submerged in could remain stuck to the electrodes. In that case, consider calling lab calibration services to get the electrodes cleaned. If the electrodes are in a good condition, you can do a number of things to keep them running smoothly. Use special washes regularly to treat the probes to maintain the special conductive surface of the probe. Follow the manufacturer’s instructions to clean the probes if the junctions in the meter become clogged.
Rinse the electrodes between samples with distilled water or deionised water. Don’t wipe them as it could cause erroneous readings due to static charges. Rather, blot the electrode’s end with lint-free paper to remove excess water.
In case of refillable electrodes, ensure that they are filled up but don’t fill them past the refill hole. Ensure that the refill hole is left open while measuring as it would ensure that the filled solution flows properly through the reference junction.
Keep the electrodes moist at all times. It is recommended that you store the electrode in a solution of 4 M KCl. If that is unavailable, you can use a pH of 4 or 7 buffer solution. Never store the electrode in distilled or deionised water as it causes the ions to leach out of the glass bulb, making the electrode useless.
Protective Rubber Boot
The electrodes are shipped with a protective rubber boot over the glass bulb in order to prevent it from cracking or scratching. Remove the rubber boot before using the electrode. When you store it long-term, put back the rubber boot with enough 4 M KCl solution to cover the glass bulb and replenish as needed to keep the bulb moist.
Regardless of what equipment you use in your facility, you must know how to calibrate instrument. Taking proper care of the electrode and handling them well can ensure you accurate pH measurement. Moreover, well-maintained and calibrated electrodes make it easier to work while measuring the pH of various liquids.
Guest Author: Edward Simpson
Author Bio: Edward Simpson works for RS Calibration Services and has a knack for finding faults in machines and does not rest until they are rectified to perfection. He lives in Pleasanton, CA and loves to write about how machines work and about the importance of proper care and calibration of equipment. When he’s not working or writing, he loves to run to stay fit.