SOP for Calibration of pH Meter (pH Tutor) : Pharmaceutical Guidelines

SOP for Calibration of pH Meter (pH Tutor)

Standard operating procedure of calibration of pH Meter.


       To describe the procedure for operation and calibration of pH meter (pH Tutor).

2.0  SCOPE

       This SOP is applicable for the operation and calibration of pH meter (pH Tutor).


       Officer/ Executive - Quality Control


       Manager - Quality Control


5.1  Operation of pH meter (pH Tutor)

5.1.1  Ensure that the instrument is on clean and dry platform.
5.1.2  Ensure that the instrument is clean.
5.1.3  Switch on the main power supply to the instrument.
5.1.4  Press ‘ON / OFF’ switch, it will display “MEAS” pH and temp.” mode on the screen.
5.1.5  Ensure that the instrument is calibrated.
5.1.6  Remove the pH electrode from the storage solution and rinse it with purified water 2-3 times. Soak the excess water with tissue paper and insert the pH electrode.
5.1.7  Stir the sample solution keeping the pH electrode.
5.1.8  Allow stabilizing the pH and then record the pH. The display shows the pH of your sample, temperature in °C,
5.1.9  Rinse the electrode with purified water and soak the excess water with tissue paper between measurements.
5.1.10  After completion of pH measurement rinse the electrode and temperature sensor with the purified water, soak the excess water with tissue paper and insert the pH with temp. sensor electrode  in the storage solution (saturated potassium chloride solution).
5.1.11  After measurement enter details in usage log book.

5.2  Calibration of pH meter:

5.2.1  Preparation of buffer solutions for standardization.

5.2.2  Buffer solution pH 4.01: 

Dissolve 1.021 g of potassium hydrogen phthalate (previously dried at 110ºC for 2 hours) in sufficient distilled water to produce 100 ml. Mix thoroughly to get uniform concentration.

5.2.3  Buffer solution pH 7.0 : 

Mix 13 ml of 2.1 % w/v solution of citric acid with 87 ml of 7.15% w/v solution of disodium hydrogen phosphate.

5.2.4  Buffer solution pH 10.0:

Dissolve 5.4 gm of ammonium chloride in 20 ml of water, add 35 ml of 10 M ammonia and dilute with water to 100 ml.
5.2.5  Allow the instrument to stabilize for at least 15 minutes before performing, daily calibration.
5.2.6  Press ‘CAL / MEAS’ button for calibration, CAL will be display on the screen.
5.2.7  Calibrate the instrument by the standard buffer solution alternatively of pH 4.01, 6.87 and 9.18 at 25 ºC ± 2 ºC.
5.2.8  Press ‘CAL / MEAS’ button, CAL will be display on the screen. Check the standard value of buffer solution pH 4.01, 7.00 and 10.00 and record in log book..
5.2.9  Storage of buffers: Buffer solution shall not be stored more than 7 days. Store the buffer solution in glass bottle; use the buffer solution if the buffer solution is clear during the storage.
5.2.10  Storage of electrode: Store the electrode in saturated potassium chloride solution. Change the saturated potassium chloride solution weekly. Do not store the pH electrode in distilled water or purified water.
5.2.11  Frequency of calibration: Daily before use and after maintenance.

5.3  Precautions

5.3.1  Do not leave the electrode dry, when not in use, keep the electrodes in buffer solution of pH 7.0 + potassium chloride (1 gm of potassium chloride in 100 ml of buffer).
5.3.2  Do not wipe the glass electrode bulb with any coarse material. Use only tissue paper.
5.3.3  The buffers should not get contaminated and should not be used after seven days.


6.1  SOP  - Standard Operating Procedure
6.2  No. - Number
6.3  QA - Quality Assurance
6.4  NA - Not Applicable
6.5  CCF - Change control format
6.6  QC - Quality Control

Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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