Calibration of pH meter

BACKGROUND OF pH meter

Calibration of any instruments is necessary to ensure its own precision and accuracy in providing results / readings.¹ pH meter is used to find out the pH of sample being studied. Solutions with different pH are used to calibrate the pH meter.²

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REQUIREMENTS

• pH meter
• Lint free tissue paper e.g. Kimwipes
• Buffer with pH value 7.0
• Buffer with pH value 4.2
• Buffer with pH value 9.6

PROCEDURE

Preparation of buffer (pH 7.0)

Add 100 ml 0.1 M KH₂PO₄ in a beaker containing about 50 ml of distilled water, then slowly add 58.2 ml of 0.1 M NaOH and make up the volume up to 200 ml with distilled water, stir well for proper mixing.

Preparation of buffer (pH 4.2)

Add 100 ml 0.1 M potassium hydrogen phthalate in a beaker containing about 50 ml of distilled water, then slowly add 6.0 ml of 0.1 M NaOH and make up the volume up to 200 ml with distilled water, stir well for proper mixing.

Preparation of buffer (pH 9.6)

Add 100 ml 0.025 M Na₂B₄O₇.10H₂O (borax) in a beaker containing about 50 ml of distilled water, then slowly add 22.2 ml of 0.1 M NaOH and make up the volume up to 200 ml with distilled water, stir well for proper mixing.

Instrumentation

Switch on the pH instrument, wait for at least 5 minutes (electrode dipped in distilled water).

Take out the electrode from distilled water, dry with lint free tissue paper by gentle rubbing ensuring no particle remains in electrode. Dip the electrode in buffer with pH 7.0, wait for few minute (for stabilization) and press the calibrate button key of the instrument. After getting stabilized reading press measure key so that instrument will set value of the buffers pH.

Remove the electrode, rinse with distilled water, and repeat the above procedure with other two buffers. The instrument is calibrated and is ready for measuring pH of samples. After taking pH readings of samples clean and dip the electrode with distilled water.

CONCLUSION

Calibration of pH instrument ensures precision of instrument itself and accurate pH measurement of samples.

REFERENCES

1. https://www.wikihow.com/Calibrate-and-Use-a-pH-Meter. Accessed on 03 August 2017.
2. http://delloyd.50megs.com/moreinfo/buffers2.html. Accessed on 03 August 2017.

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• Acute toxicity testing for topical preparations
• Calculation of Body Surface Area (Using a Nomogram)
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