Good Laboratory Practice: Handling and Care of pH meter

A pH meter can be seen in all laboratories irrespective of size – School laboratory College laboratory, University research laboratory, Commercial products testing

laboratory, Industrial laboratory or even a national level laboratory.

A laboratory may not be equipped with sophisticated instruments such as AAS, GC, HPLC, LC – MS or FT – IR but it simply cannot do without a pH meter as pH measurement is a basic requirement for all chemical and biochemical reactions and process control reactions in manufacturing industries.

Even a slight variation in prescribed acidity can change the course of reactions or lead to manufacturing losses. 

Yet the simple pH meter is often taken for granted and its proper handling and care are overlooked.

Here are some valuable tips on proper handling and care of a pH meter that will ensure correct pH reading every time you make use of it :

1.     A pH electrode is fragile and one should not be tempted to use it as a stirring glass rod when adjusting pH.

2.     A pH meter needs to be calibrated daily with the help of standard buffer solutions.

3.     pH readings are temperature-sensitive due to changes of glass electrode resistance. A 10-fold increase in resistance results for every 30°C rise in temperature. Avoid temperature fluctuations and never keep the pH meter exposed to direct sunlight.

4.     The glass electrode should not be left out of the storage solution for prolonged intervals as the glass membrane gets dehydrated resulting in slower response and can eventually lead to complete response failure. The electrode should not be immersed in dehydrating solutions such as sulfuric acid and ethanol.

5.     Glass is rapidly attacked by hydrofluoric acid so never keep the electrode in HF solution as it can lead to irreparable damage of the electrode.

6.     Avoid vibrations and shock. When using magnetic stirrers take care to maintain adequate distance between meter bulb and the magnetic stirrer pellet to prevent accidental breakage. A heated magnetic stirrer should never be used as it can bring about a change of temperature of the solution.

7.     Handle carefully during inter-or intra laboratory transport to prevent breakage.

8.     Store sensors at ambient temperatures of 10°C to 30°C. Protective caps as well as solution storage caps provided by the supplier should be installed onto the end of the sensor when not in use. Ideally the sensor should be stored in 3 to 3.5 M KCl solution. Keep a check to ensure that the storage solution has not evaporated.

9.     Adopt the suggested cleaning procedures after use:

• General cleaning – if the solutions are fairly clean soak in 0.1M HCL or 0.1M HNO₃ for about 30 minutes
• Bacteria or deposits – soak in 1: 10 dilution of laundry bleach for 10 min
• Oil or grease – soak in detergent or methanol
• Protein deposits – soak in 1% pepsin in 0.1 M HCl for 5 min.

After every soaking the electrode should be rinsed with distilled water. Droplets adhering to electrode should be gently dried with tissue paper and not rubbed or wiped.