OBJECTIVE:
To lay down the procedure for Operation and Calibration of pH Meter.
SCOPE:
This procedure is applicable for the Operation & Calibration of pH Meter being used in Quality Control Laboratory.
RESPONSIBILITY:
Quality Control Officer / Executive is responsible to follow procedure as per the procedure mentioned in this SOP.
QC Head is responsible for implementation and compliance of the procedure as per this SOP.
ABBREVIATIONS
SOP : Standard Operating Procedure
QC : Quality Control
QA : Quality Assurance
PROCEDURE:
Operation
Ensure that the working bench and instrument is clean.
Connect the instrument to the mains power.
Switch on the instrument.
Plug the ‘RTD’ probe (Temp. sensor) to the socket provided.
Rinse the electrode with distilled water.
Wipe out the water from the electrode with tissue paper.
Calibrate the instrument as described under section 5.2.
Rinse the electrode and RTD probe with water and wipe out with tissue paper.
Dip the electrode and RTD probe in sample solution.
Press the key pH to read pH value and temperature.
After every measurement of the sample clean the electrode with distilled water.
Don’t keep the electrode in dry condition, to avoid it place the electrode in pH 4.00 buffer solution only.
Don’t store the electrode in distilled water.
Calibration Procedure
Preparation of Buffer Solution (Five point Calibration)
Prepare the standard buffer solutions of pH 1.68, 4.00, 7.00, 9.20 & 12.45 at 25°C as follows and record as per Preparation of Buffer Solution (Annexure I).
Buffer solution pH 1.68:- Transfer the contents from buffer capsule 1.68pH in a 100 ml volumetric flask containing about 80ml distilled water, dissolve it completely and make up the volume with distilled water.
Buffer solution pH 4.00:- Transfer the contents from buffer capsule 4.00pH in a 100 ml volumetric flask containing about 80ml distilled water, dissolve it completely and make up the volume with distilled water.
Buffer solution pH 7.00:- Transfer the contents from buffer capsule 7.00pH in a 100 ml volumetric flask containing about 80ml distilled water , dissolve it completely and make up the volume with distilled water.
Buffer solution pH 9.20:- Transfer the contents from buffer capsule 9.20 pH in a 100 ml volumetric flask containing about 80ml distilled water , dissolve it completely and make up the volume with distilled water.
Buffer solution pH 12.45:- Transfer the contents from buffer capsule 12.45 pH in a 100 ml volumetric flask containing about 80ml distilled water , dissolve it completely and make up the volume with distilled water.
Keep the above five buffer solutions in five different glass bottles, appropriately, labeled as per Label For Buffer Solution (Annexure II).
Clean the electrode with distilled water and wipe it with tissue paper.
Standardization of Buffer 7.0 pH
Take pH 7.00 buffer in a clean dried beaker, dip the electrode and RTD probe in the buffer.
Press memory clear key and enter 3 for all clear. Press pH key. After the readout of pH value, press cal 7 key. Press enter key and wait for stabilizing the mv value. When stabilized mv value is displayed press enter.
Note down the temperature and pH of the buffer after the display shows standardization over.
Remove the electrode and RTD probe and rinse with distilled water and wipe out with tissue paper.
Select pH 1.68, pH4.00, pH 9.20 and pH12.45 buffer one by one.
Dip the electrode and RTD probe in the buffer and repeat the procedure as mentioned for pH 7.00 by pressing key cal, 1.68, cal 4, cal 9 and cal 12.45. The display shows calibration over.
If the pH values are within limits as given in the table below. Calibration is O.K.
pH buffer | pH |
pH 1.68 | 1.68 ± 0.05 |
pH 4.00 | 4.00 ± 0.05 |
pH 7.00 | 7.00 ± 0.05 |
pH 9.20 | 9.20 ± 0.05 |
pH 12.45 | 12.45± 0.05 |
Prepare the buffers freshly after every 7 days.
Close the lids immediately after use.
If any Turbidity found in buffers, discard the buffer solution and prepare the buffers freshly.
Record the calibration as per Daily Calibration of pH Meter (Annexure III).
Calibration frequency – daily.
If the instrument is out of calibration tag the instrument with the following label. Inform to the service engineer for rectification. Calibrate the instrument after rectification.