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SOP for Calibration of pH Meter (GMPH)


Standard operating procedure of calibration of pH meter using buffer solutions of 7.00, 4.00, 9.20 pH.

1.0  OBJECTIVE

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

2.0  SCOPE

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

3.0  RESPONSIBILITY

       Officer/ Executive - Quality Control

4.0  ACCOUNTABILITY

       Manager - Quality Control

5.0  PROCEDURE

5.1  Operation of pH meter (GMPH)

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 the temperature switch to display the temperature. Put the meter in Measure Mode by pressing stand by switch. This mode is indicated by the RED light.
5.1.5  Ensure that the instrument is calibrated. If instrument is not calibrated, calibrate the instrument before use.
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.
5.1.7  Insert the pH electrode and temperature sensor in a sample solution. The temperature of the solution is displayed
5.1.8  Stir the sample solution keeping the pH electrode and resistant temperature detector immersed.
5.1.9  Allow stabilizing the pH and then record the pH. The display shows on the screen.
5.1.10  Rinse the electrode with purified water and soak the excess water with tissue paper between measurements.
5.1.11  After completion of pH measurement rinse the electrode and temperature sensor with purified water, soak the excess water with tissue paper and insert the pH electrode and temperature sensor in the storage solution (100 ml Buffer pH7 + 1 gm KCl).
5.1.12  After measurement enter details in usage log book.

5.2  Application of STAND by feature

5.2.1  This feature is used after the calibration is completed. It avoids recalibration in absence of the original buffer or when the STD & CAL. Knob are disturbed without information

5.3  Operation of STAND by feature

5.3.1  Press the stand by switch after the calibration to put the meter in stand mode. This is indicated by lighting of the LED. Now note down the mV and pH that are displayed by pressing respected key. The note value are used later to recalibrate the meter, without using the buffer.
5.3.2  To recalibrate the meter, put the meter in standby  mode. Press the mV switch and adjust the STD. Knob to get the value on the display as noted earlier. Now press the ph switch and adjust the CAL. Knob to get the pH value noted earlier. Put the meter in measure mode by using stand by switch again. Now the unit is ready for continuing the ph measurement.

5.4  Calibration of pH meter:

5.4.1  Preparation of buffer solutions for standardization.
5.4.2  Buffer solution pH 1.68 : Dissolve 5.355 g of potassium tetra oxalate in sufficient distilled water to produce 500 ml. Mix thoroughly to get uniform concentration.

5.4.3  Buffer solution pH 4.01 : 

Dissolve 5.105 g of potassium hydrogen phthalate (previously dried at 110ºC for 2 hours) in sufficient distilled water to produce 500 ml. Mix thoroughly to get uniform concentration.

5.4.4  Buffer solution pH 5.87 : 

Dissolve 1.70 g of potassium dihydrogen phosphate and 1.775 g of anhydrous disodium hydrogen phosphate both previously dried at 110ºC to 130ºC for two hours, in sufficient distilled water to produce 500 ml. Mix thoroughly to get uniform concentration.

5.4.5  Buffer solution pH 9.18 : 

Dissolve 1.907 g of di-sodium tetra borate (previously dried at 110ºC for 2 hours) in sufficient distilled water to produce 500 ml. Mix thoroughly to get uniform concentration.

5.4.6  Buffer solution pH 12.45 : 

Shake an excess of Calcium Hydroxide with water, and decant at 25 ºC before use . Protect from absorption of Carbon dioxide.
5.4.7  Allow the instrument to stabilize for at least  5 minutes before performing daily calibration.
5.4.8  Insert the pH electrode and temperature sensor in a solution of standard 7.00 pH. The temperature of the solution is displayed.
5.4.9  Press the pH switch to display the pH. Let the reading on display to stabilize. Now adjust the STD. Knob so that the display indicates 7.00. This operation is known as STANDARDISATION.
5.4.10  Now insert the pH electrode and temperature sensor in a solution of standard 4.00 or 9.20 etc. Wait until the reading stabilizes. Now adjust the CAL Knob so that correct pH value of the buffer is displayed. This operation is known as CALIBRATION.
5.4.11  Now put the instrument in standby mode & note the display value by pressing pH and mV switches respectively.
5.4.12  Removing the pH and temperature sensor and rinse in purified water. Shake the electrode remove the residual solution. Wipe the sensor extremely with clean tissue paper without touching the bulb of pH sensor.
5.4.13  The meter and sensor are now ready for the measurement the pH of the sample solution. The display is automatically temperature compensated for span error in pH sensor due to temperature other than 25 ºC   
5.4.14  Note down the readings of buffer 7.00, 4.00, 9.20 respectively as per operation procedure and note down the observation.
5.4.15  Frequency of calibration: Daily before use and after maintenance.
5.4.16  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.
5.4.17  Storage of electrode: Store the electrode in saturated Potassium chloride solution. Change the saturated Potassium chloride solution monthly. Do not store the pH electrode in distilled water or purified water.

6.0  ABBREVIATIONS

6.1  SOP - Standard Operating Procedure
6.2  No. - Number
6.3  QA - Quality Assurance
6.4  QC - Quality Control
6.5  CCF - Change control format



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