How to Care for and Extend the Lifetime of pH Meters
We all know the value of pH meters in the science laboratory—they are very sensitive instruments that provide accurate and instant pH readings. Often, pH meters are overused and not properly maintained.
Maintenance of these valuable instruments is not difficult and can easily be done by following a few simple steps. Let’s explore some tips and tricks to get the most accurate and precise readings out of your pH meters.
Calibration of pH meters is an essential step to extend the lifetime and achieve accurate results. A pH meter needs to be calibrated before each use by using standard buffer solutions close to the pH range of the experiment. The three most commonly used buffer solutions are pH 4.0, 7.0 and 10.0. Other buffers can also be used based on the pH use range.
Most pH meters have one probe that contains two different electrodes (glass and reference—often referred to as combination electrode). The glass electrode is essential in reading pH, and must be kept hydrated (submerged in a liquid). The glass electrode is usually stored in a buffer solution of about pH 4.
This electrode should always be stored in the storage solution since it dries out quickly. If the digital readings displayed are incorrect or arbitrary, this usually means that the electrode may have dried out. If the electrode dries out, it can be revived by submerging in a saturated potassium chloride solution for about 3-6 days, monitored daily. Once the electrode is hydrated, it can be calibrated as usual.
Storage and Handling
The pH meter readings are temperature sensitive. Never store pH meters in high heat or humidity. Do not expose pH meters to direct sunlight. Store pH meters away from hazardous chemicals and handle carefully during a move or internal transfer to prevent damage.
Never touch the electrode without gloves (the oils on the skin affect the readings and can damage the electrode).
When using pH meters in a solution being stirred with a magnetic stirrer, use low-to-medium speed. Never expose glass electrodes to harsh chemicals such as hydrogen fluoride. They can damage (etch) the glass.
Finally, when needed use the following proper cleaning procedures:
- General cleaning – soak in 0.1 M hydrochloric acid or 0.1 M nitric acid for about 30 minutes
- Oil or grease – soak in detergent or methanol
- Protein deposits – soak in 1% pepsin in 0.1 M hydrochloric acid for 5 min
- Rinse the electrode with distilled water after soaking and gently dry the electrode with regular tissue paper or lens cleaning paper
These tips will extend the life of your pH meters and maintain accuracy and precision of your readings.