SOP -OPERATION AND CALIBRATION PROCEDURE FOR pH METER. ( MAKE: DIGISUN)

1.0 Objective

To ensure that the instrument performs satisfactorily and gives accurate and reproducible results.

2.0 SCOPE

This SOP Covers the operation and calibration procedure for pH meter and is applicable to Quality Control Department.

3.0 Responsibility

Officer / Executive.

4.0 Accountability

Department Head

5.0 PROCEDURE

5.1 Procedure for general cleaning

5.1.1 Ensure that the power supply to the instrument is switched OFF before cleaning.

5.1.2 De dust the equipment daily externally with a clean dry cloth.

5.1.3 Once in a week remove adhered dust by wet mopping using detergent solution. Afterwards wipe the surface with a clean dry cloth to remove traces of detergent.

5.1.4 Precaution has to be taken to clean the instrument immediately with dry cloth to remove the moisture.

5.2 OPERATING PROCEDURE

5.2.1 Switch on the instrument using power on/off switch in the rare of the instrument. Warm up the instrument for just a minute or two.

5.2.2 Keep the SELECTOR in pH mode and the TEMP control knob at 250 C.

5.2.3 The display should read 7.00, otherwise adjust the pH to 7.00 by using the SET 7.0 knob and keep the SELECTOR in HOLD position and keep the push button in calibrate mode only.

5.2.4 Wash the electrode with distilled water and wipe of the moisture.

5.2.5 Dip the electrode in sample beaker and stir the beaker for a while.

5.2.6 Release the push button switch after a minutes stirring of beaker and record the pH of the sample.

5.3 CALIBRATION

5.3.1 Preparation of standard buffer solution.

5.3.1.1 Buffer pH 4.01 : Prepare a 1.021 % w/v solution of Potassium hydrogen phthalate, previously dried at 110 to 135°C for 2 hours.

5.3.1.2 Buffer pH 6.87 : Prepare a mixture 0.340%w/v solution of Potassium dihydrogen phosphate and 0.355 % w/w solution anhydrous disodium hydrogen phosphate, both previously dried at 110 to 135°C for 2 hours.

5.3.1.3 Buffer pH 9.18 : Prepare 0.3814 % w/v solution of Sodium tetraborate. Protect this solution from carbon dioxide.

5.3.1.4 Set the instrument by using pH 4.01 buffer solution and pH 9.18 buffer solutions

5.3.2 Repeat the operations 5.2.1 to 5.2.4

5.3.3 Take the 4.01 buffer into a suitable beaker and dip the electrode into it and stir for a while, release the push button to read the pH.

5.3.4 If it should read 4.01, otherwise adjust it to 4.01 by adjusting the Slope screw which is provided at rear of the instrument.

5.3.5 Turn the SELECTOR to hold position and push button to Read position.

5.3.6 Take out the electrode and wash with water, wipe of the moisture.

5.3.7 Take the 9.18 buffer into a suitable beaker and dip the electrode into it and stir for a while, adjust SET BUFFER screw to 9.18 .

5.3.8 Turn the SELECTOR to hold position and push button to check position.

5.3.9 Take out the electrode and wash with water, wipe of the moisture.

5.3.10 Calibrate the instrument with 6.87 buffer solution.

5.3.11 Take the 6.87 buffer solution into a suitable beaker and dip the electrode into it and stir for a while, release the push button to read the pH.

5.3.12 Measure the pH and record in the format as per Annexure – I

5.4 FREQUENCY OF CALIBRATION

5.4.1 Calibrate the instrument everyday before using the instrument

5.5 SAMPLE MEASUREMENT

5.5.1 Before sample measurement Select two Buffer solutions for standardization whose difference in pH does not exceed 4 units and such that the expected pH of the material under test falls between them.

5.6 TROUBLE SHOOTING

5.6.1 Report any discrepancy observed during operation or calibration monitoring to Quality Control Executive and notify the defect to maintenance department
for rectification. Affix “BREAK DOWN” label on the instrument.

5.7 ACCEPTANCE CRITERIA

5.7.1 The pH of 6.87 buffer solution buffer should be within + 0.05

6.0 REASON FOR REVIEW

First time issue.