How to Perform Calibration of pH Meter

Table of contents

• Calibration Description
  • Reagents and instruments
  • General
  • Scope
  • Responsibility
• Frequency
• Procedure
• Buffer preparation

Calibration Description

Reagents and Instruments

• Purified water (carbon dioxide free)
• pH 1,68, pH 4.01, pH 8.96, pH 9.18 and pH12.45 buffer*

Note*:

• Nowadays readymade-commercial buffer (with valid COA) are used for the calibration of pH meter
• See the buffer preparation section of this post to prepare the same in the laboratory

General

For the smooth running of pH meter and to achieve precision, accuracy, and repeatability in analysis calibration of the pH meter is required

Scope

The procedure applies to all pH meters of the company

Responsibility

Research Scientists/Chemists/Analysts responsible for the calibration of the instruments

HOD

To ensure the compliance of the SOP in the Analytical development laboratory or Quality control Laboratory (as applicable)

Frequency

Daily

Procedure

1. Follow the operational SOP for the operation of the instrument
2. Select the calibration mode
3. Select the Linear regression interpolation method from the calibration mode
4. Enter first value as 1.68 and enter
5. Dip the electrode and the temperature probe in pH 1.68 solution
6. Wait to stabilise the reading . Once the reading stabilise press enter
7. Remove the electrode from the pH 1.68 buffer and rinse it thoroughly with purified water
8. Soak the excess water with tissue paper
9. Insert the pH electrode and sensor in the beaker having a pH 4.01 solution
10. Repeat the above steps (1 to 9) for pH 4.01. pH 6.86, pH 9.18 and pH 12.45
11. Record the result in the calibration sheet
12. After completion of the above 5 pints buffer pH checking calculate the slope
13. If the pH meter slope lies within the limit report of the value (of the buffer used and the slope obtained)

Acceptance Criteria: 90 to 105%

Tolerance: ± 0.05 Standard pH buffer

pH Buffer Preparation in the Laboratory

1. pH 1.68: Weigh accurately about 1.271 gm of potassium tetraoxalate and transfer it to 100 ml volumetric flask and make the volume with water. Sonicate to dissolve
2. pH 4.01: Weigh accurately about 1.021 gm of Potassium phthalate and transfer to 100 ml of volumetric flask and make the volume with water, Sonicate to dissolve
3. pH 6.86: Weigh accurately about 348 mg of Potassium dihydrogen phosphate and 355 mg of anhydrous Disodium Hydrogen phosphate and transfer to 100 ml of volumetric flask and make the volume with water, Sonicate to dissolve
4. pH 9.18: Weigh accurately about 381.4 mg of Sodium tetraborate and transfer to 100 ml of volumetric flask and make the volume with water, Sonicate to dissolve
5. pH 12.45: Prepare saturated solution of Calcium hydroxide in water (Shake excess of Calcium hydroxide and decant before use)

Abbreviations:

• HOD: Head of department
• Std: Standard
• SOP : Standard operating procedure
• pH: Potential of Hydrogen
• COA: Certificate of Analysis
• gm: Gram

References:

• USP
• IP