SOP FOR OPERATION AND CALIBRATION OF pH METER
PURPOSE: To lay down a procedure for Operation and Calibration of pH meter.
SCOPE: This SOP is applicable for operation and calibration of pH meter.
RESPONSIBILITY:
Preparation of SOPs: Officer QA Department
Checking and Review of the SOPs: Sr. Officer QA Department
Approval of the SOPs: Executive QA Department
Authorizing of SOP: Head QA/Designee
ACCOUNTABILITY: Head QA shall be accountable for the Implementation and Compliance for this SOP.
PROCEDURE:
Operation
Ensure that the instruments are clean and free from dust.
Rinse the glass beaker with Purified water and sample for three times.
Maintain the temperature of solution to 25oC unless otherwise stated.
Rinse pH electrode with Purified water.
Switch ON the main power of the instrument.
Check meter using standard solution that is nearest ±0.05 units the expected pH.
Fill test tube with sample.
Immerse electrode in sample while swirling the sample to provide through mixing. Electrode filler level should be % inch above sampling surface level. Read pH to nearest ±0.1 unit.
Record the pH of Sample.
Rinse the electrode with Purified Water and store According to manufacturer’s direction.
Record the operational activity as per Format.
Calibration
Ensure that the instruments are clean and free from dust.
Rinse pH electrode with purified Water.
Maintain the temperature of all the standard solutions to 250C.
Immerse the electrode in beaker of calibration standard solution of pH-1.68, Switch ON the main power of the instrument. Calibrate pH meter to appropriate pH.
Remove electrode from solution, rinse with Purified water and mope with tissue paper.
Immerse the electrode in second calibration standard solution of pH – 4.01 calibration pH meter to appropriate pH.
Remove electrode from solution, rinse with purified water and mope with tissue paper.
Immerse electrode in third calibration standard solution of pH-6.87. Calibrate pH meter to appropriate pH.
Remove electrode from solution, rinse with Purified water and mope with tissue paper.
Immerse electrode in third calibration standard solution of pH-9.18. Calibrate pH meter to appropriate pH.
Remove electrode from solution, rinse with Purified water and mope with tissue paper.
Immerse electrode in third calibration standard solution of pH-12.45. Calibrate pH meter to appropriate pH.
Calibration slope of electrode should lies between 95% to 105%.
Then verify the pH of the calibrates pH meter from calibration standard solution.
Reading of the calibration standard does not differ by ±0.05 of the actual value.
Remove electrode from solution, rinse with purified water and store according to manufacturer’s direction.
Frequency: At the beginning of each day of field work when pH will be measured or after any maintenance or change of electrode.
Record the observation as per Format.
Electrode Rejuvenation :
If the electrode fails to give appropriate result during calibration, the same shall be rejuvenated as mentioned below:
Dip and stir the electrode in ethyl alcohol for 5 min.
Leave the electrode in tap water for 15 min.
Dip and stir the electrode in 0.1 M Hydrochloric Acid for 60 min.
Leave the electrode in tap water for 15 min.
Test with standard calibration buffer solution.
If the electrode still fails to restore the normal electrode response, the electrode rejuvenation shall be repeated.
If response does not improve, then the electrode has completed its useful life and same shall be replace with a new electrode.
Preparation of pH Buffer Solution:
pH Buffer 1.68: Weight 1.271 g of potassium tetra oxalate and transfer in to 100ml Volumetric flask dilute with water to 100ml.
pH Buffer 4.01: Weight 1.021 g of potassium hydrogen phthalate previously dried at 1100C to 1350C for 2 hours and transfer into 100ml volumetric flask dilute with water to 100ml.
pH Buffer 6.87: Weight 0.348 g of potassium dihydrogen phosphate and 0.355g of anhydrous disodium hydrogen phosphate and both are previously dried at 1100C to 1300C for 2 hours and transfer in to 100ml volumetric flask dilute with water to 100ml.
pH Buffer 9.18: Weight 0.3814 g of sodium tetra borate and transfer in to 100ml volumetric flask dilute with water to 100ml.
pH Buffer 12.45: Shake on excess of calcium hydroxide with carbon dioxide free water and decant at 250C.
Storage:
Always keep the electrode bulb wet, preferably in the 4.01 pH buffer.
During handling of pH meter, check if electrode is broken, replace the same with new electrode and enter the details in instrument usage logbook for pH meter.
pH buffer solution shall be used within week (7 days) and stored at room temperature. If the buffer solution found precipitate and the pH value found unsatisfactory than prepared pH buffer freshly.
REFERENCE:
SOP FOR SOP