SOP for Operation and Calibration of pH Meter | pH Meter Calibration as per USP

This document details the procedure for the operation and calibration of the pH meter. It is the policy of pharmaceuticals that the written procedure shall be followed for the operation and calibration of pH Meter in order to ensure smooth operation and its use monitored to obtain consistent and reproducible results to minimize downtime and to meet regulatory requirements.

This procedure is to be applied at the time of operation and calibration of the pH meter.


Persons along with their responsibilities and account-abilities are given below:

S. No





Executive - Corporate Quality Assurance

To prepare the SOP and follow the same



Trainee Analyst/ Jr. Analyst/ Analyst/ Sr. Analyst

To follow the SOP accordingly


Manager - Quality  Assurance

To ensure implementation of SOP.


Manager- Quality Control

To ensure implementation of SOP.   


Manager      -      Technical

To ensure implementation of SOP.



VP              -       Technical

To ensure implementation of SOP.



Manager – Corporate Quality Assurance

To ensure implementation of SOP.

5.0 General instructions

5.0.1 Check the validity of the buffer solutions before use.

5.0.2 After calibration do not switch off the pH meter. If done so, again calibrate the pH meter before use.

5.0.3 To remove excess water from the electrode gently touch it over with a small piece of filter paper/ tissue paper. Never rub the electrode with filter paper/tissue paper.

5.0.4 If the pH meter is not in use for more than 48 hours, then immerse the electrode in saturated aqueous Potassium Chloride solution.

5.0.5 for regeneration, periodically dip the pH electrode in 1M HCL for 10-15 minutes and then rinse with purified water. Check the liquid in the electrode, the electrode filament should be dipped completely in the liquid; if not saturated potassium chloride solution should be injected up to the required level.

CLEANING of pH meter

Disconnect the apparatus from the main power supply.

Clean the apparatus externally with the help of a clean dry cloth daily. If required clean with a wet cloth followed by a dry cloth.

Clean the electrode with Purified water. If required immerse the electrode in 0.1 M HCL or 0.1 M HNO3 for 30 minutes. After immersing the pH electrode in an acidic solution wash with Purified water properly.

5.2  pH meter PRECAUTIONS

5.2.1 Do not leave the electrode dry. Keep the electrode in a storage medium (slightly acidic Solution).

5.2.2 Do not wipe the glass electrode bulb with any coarse material. Use only tissue paper.

5.2.3 The buffer solution should not get contaminated and should not be used after one month.

5.2.4 Before preparation of new Buffer solution discard previous buffer solution and if there is haziness in buffer due to fungal growth discard the solution and prepare freshly buffer.

Operation and calibration of pH meter | pH meter calibration as per USP


5.3.1 Calibrate the pH meter at the start of each working day before use.

5.3.2 Switch on the pH Meter, allow it to stabilize for 15 minutes, and follow step 5.4.

5.3.3 Rinse the electrode with Purified water.

5.3.4 Calibrate the instrument by using buffer solution.


5.3.6  Preparation of Buffer Solutions Acid Phthalate buffer (pH 4.01) Place 250 ml of potassium biphthalate solution in 1000ml volumetric flask, add 0.5mL of (0.2M) hydrochloric acid solution, and add water to volume. Record the preparation details of buffer solution on SOP Preparation of stock (Buffer) solution, once in a month and store at room temperature in plastic bottles. Phosphate buffer (pH 7.01) Place 250 ml of the monobasic potassium phosphate solution in a 1000 ml volumetric flask, add 145.5 ml of sodium hydroxide (0.2M) NaOH, then add water to the volume Record the preparation details of buffer solution on SOP  Preparation of stock (Buffer) solution,  once in month and store at room temperature in plastic bottles Alkaline Borate Buffer (Ph 10.01) Place 250ml of the boric acid and potassium chloride solution in 1000ml volumetric flask, add 218.5 volume of sodium hydroxide solution (0.2M NaOH) then add water to volume Prepare buffer solutions on SOP Preparation of stock(Buffer) solution,  once in month and store at room temperature in plastic bottles

5.3.7 Transfer 100 ml of each stock buffer solution in 100 ml individual plastic bottles for daily calibration  and record the transfer volume on SOP as Preparation and Transfer record Appendix for  pH 4.01, for pH 7.01 record the transfer volume on SOP as Preparation and transfer record Appendix  and for pH 10.01 record the transfer volume on SOP as Preparation and Transfer record

5.3.8 For Daily calibration transfer the required volume in the beaker from 100 ml plastic bottles and again pour this buffer solution in the plastic bottle after use.

5.3.9 After one week discard the buffer solution from a 100ml plastic bottle and again fill this bottle from the stock buffer solution  

5.3.10 alternatively, uses commercially available liquid buffer solutions and follows step 5.3.7.

5.3.11 Allow solutions to attain room temperature before being used for calibration by using the temp knob provided on your instrument.

5.3.12 Connect the electrode to the pH meter (if not connected). Select buffer solutions of pH 4.01, 7.01 10.01.

5.3.13 Immerse the electrode in the buffer solution pH 4.01  Wait till the screen shows a stable value and press the Call key.

5.3.14 Rinse the electrode with Purified water, blot out the water with tissue paper/ filter paper, and place it into a buffer solution. Wait for a stable pH reading and ready signal to appear on the display and perform the same till the last buffer value has been entered

5.3.15 Same procedure is repeated for buffer solution of pH 7.01,10.01.

5.3.16 pH meter is calibrated if pH readings differ by not more than 0.05 from the set reading and record the observations

5.3.17 Record the Calibration Data on CQA/SOP-050/FR-02 as the Daily Calibration Record of pH Meter Appendix II.

5.3.18 Compare the result with acceptance criteria and take valid calibration authorization from Section Incharge.

5.3.19 Report any discrepancy observed during operation and calibration of instrument to Section Incharge or his representative for corrective and preventive action.

5.3.20 Section Incharge or his representative will report the same to the Manager – Quality Assurance and notify the defect to service engineer to rectify the defect.

5.3.21 Affix ‘Out of Order’ label on the instrument.


5.4.1 Switch On the pH meter from main power.

5.4.2 Use the ON / OFF key present at the backside of the pH meter.

5.4.3 The following keys are used during operation and calibration. 

For pH measurement, first, check the calibration of the pH meter as mentioned in 5.3.1 to 5.3.22. Rinse the electrode with Purified water and ensure that the pH meter is in measure mode (by pressing the Result key) to measure the pH of the test solution.

5.4.6 Dip the electrode tip in the test solution.

5.4.7 Wait for a stable pH reading and ready to appear on display.

5.4.8 Rinse the electrode with Purified water.

NOTE-Do does not immerse the entire electrode in the solutions; only the tip of the electrode should be Dipped.

5.4.9 Maintain Logbook of pH meter CQA/SOP-050/FR-01 Logbook of pH meter (Appendix I).


5.5.1 For a fast response of the pH electrode during sample measurement, the electrode is to be immersed in a slightly acidic solution.

PH electrodes should always be stored in a moist condition, in either a 7.00-pH buffer with potassium chloride solution (200 ml of buffer pH 7.0 with 1.0 gm Potassium Chloride) between routine measurements. The electrode should not store in distilled or de-ionized water.

APPENDIX I                                     /CQA/SOP-050/FR-01


Instrument ID: ----------------------------

Location: ----------------------------

APPENDIX  II                     /CQA/SOP-050/ FR-02


Instrument Id: ------------------------------

Location: ------------------------------                                                      


Observed pH of buffer  solution used

 Done by

Checked by


pH 4.01 ±0.05

(3.96 - 4.06)

pH 7.01 ±0.05

(6.96 -7.06)


pH 10.01 ±  0.05

(9.96 -10.06)























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