pH Meter - Operation & Calibration

pH METER
SOP FOR OPERATION

1.0 OBJECTIVE
To lay down a procedure for operation of pH¬ meter (Model pH scan-2).

2.0 SCOPE
This SOP is applicable to Formulations Units

2.1.0 AREAS
2.1.1 D.M. plant.

3.0 RESPONSIBILITY
Jr. Technical Officer / Executive (production)

4.0 ACCOUNTABILITY
Manager - Production

5.0 PROCEDURE



5.1.0 Precautions
5.2.0 Pre Startup
5.3.0 Calibration
5.4.0 Operation.
5.1.0 Precautions
5.1.1 Do not dip the pH meter more than the minimum immersion level.
5.1.2 E1 on display indicates, “Ensure that the battery is changed”.
5.2.0 Pre Startup
5.2.1 Ensure the cap of pH meter is removed.
5.2.2 Ensure the pH meter is calibrated before usage.
5.3.0 Calibration
5.3.1 Calibration to be done with the help of standard buffer solutions of pH 4, 7 and 10.
5.3.2 Calibrate initially with buffer solution of pH 7.
5.3.3 Select a standard buffer of pH 7.
5.3.4 Press the ON/OFF button on the key pad to turn on the pH meter.
5.3.5 Press the “CAL” button to enter calibration mode.
5.3.6 Dip the pH meter electrode up to the immersion level.
5.3.7 Stir the pH meter gently and wait for the displayed valve to stabilize.
5.3.8 Press “HOLD/ CON” button to confirm and complete the calibration.
5.3.9 Repeat the same procedure for buffer solution of pH 4 and pH 10.
5.4.0 Operation
5.4.1 Dip the pH meter electrode up to the immersion level.
5.4.2 Press the ON/OFF button on the key pad to turn on the pH meter.
5.4.3 Stir the pH meter and wait the display to stabilize.
5.4.4 Observe and record the pH.
5.4.5 Press the ON/OFF button to switch off.
5.4.6 Rinse the pH meter well with purified water.



pH METER
SOP FOR CALIBRATION

1.0.PURPOSE : To provide a procedure for periodic calibration of pH meter.

2.0 SCOPE : Covers procedure for the calibration of pH meter (daily and monthly) and also for the activation of electrode and maintenance of electrode.

3.0 DEFINITION :
3.0.1 pH: pH value conventionally represents the acidity or alkalinity of an aqueous solution.

3.0.2 CALIBRATION : The set of operations which establish, under specified conditions, the relationship between values indicated by a measuring instrument or measuring system or values represented by a material measure and the corresponding known values of a reference standard.

4.0 PROCEDURE :
4.1 PREPARATION OF BUFFER SOLUTION

Buffer solution D: (pH 4.01) Dissolve 10.21 g of potassium hydrogen phthalate, previously dried at 110 degree to 130 degree for 2 hours in sufficient carbondioxide free water to produce 1000mL.

Buffer solution E: (pH 6.87) Dissolve 3.40 g of potassium dihydrogen phosphate and 3.55 gram of anhydrous disodium hydrogen phosphate previously dried at 110 degree to 130 degree for 2 hours both in sufficient carbondioxide free water to produce 1000mL.

Buffer solution G: (pH 9.18) Dissolve 3.814 gram of borax in sufficient carbondioxide free water to produce 1000.0 ml.
Store all the above solutions in alkali free glass. Label the bottle as follows:

 
Frequency of preparation : Monthly
Every week transfer 250ml of this buffer to the secondary bottle after checking for clarity and label the bottle with details as under :

Solution showing precipitation, haziness or growth of fungus shall be discarded.

4.2 CALIBRATION OF Ph METER :
Use the service beaker provided for each buffer and do not transfer the buffer from service
beaker back to the bottle. Discard after every use.

Calibrate the apparatus using 25ml from the stock solution of buffer solution D as the primary standard adjusting the meter to read appropriate pH 4.01 Plus or minus 0.05 corresponding to the temperature of solution (25degreeCPlus or minus 2 degree C). To set the scale use a second reference buffer solution either E (6.87) or G (9.18).

If the difference between this reading and the original value is greater than 0.05, the set of measurements must be repeated.
When measuring pH values above 10.0 ensure that the glass electrode is suitable for use under alkaline conditions and apply any correction that is necessary.

IMPORTANT CONDITIONS :
a) All solutions of substances being examined must be prepared using carbon dioxide free water.
b) pH determination is carried out at a temperature of 25degreeCPlus or minus 2 degree C.
c) Buffer solutions should be stored in bottles made of alkali free glass.

5.0 ACTIVATION OF ELECTRODE :
FREQUENCE : EVERY 15 DAYS

5.1 COMBINED GLASS ELECTRODE.
Soak the electrode overnight in 6 M Hydrochloric acid, next day wash repeatedly with distilled water and immerse the electrode in distilled water.

5.2 GEL FILLED ELECTRODE

5.2.1 Between measurements (upto 1 hour)
leave the electrode in an open air lab environment not in distilled water.

5.2.2 Short term storage (upto one week)
Soak electrode in 200ml pH 7 buffer added with 1 g potassium chloride.

5.2.3 Long term storage (over one week).
Cover the electrode tip with a protective cap used for shipment.

6.0 MAINTENANCE OF ELECTRODE :
CLEANING PROCEDURE
6.1 GLASS ELECTRODE
6.1.1 General : Soak electrode in 0.1 M HCl or 0.1 N HNO3 for 15 minutes.
6.2 GEL FILLED ELECTRODE :
6.2.1 Removal of Deposits
6.2.2 Protein : Digest with 1% pepsin in 0.1 M HCl.
6.2.3 Inorganic : Rinse with 0.1 M tetra sodium EDTA solution.
6.2.4 Grease and oil : Rinse with mild detergent or methanol solution.

7.0 RECORDS :
7.1 Record the pH calibration & activation of electrode in form F:Sxxxx/DPHR/A.
7.2 Record the monthly calibration in form F:Sxxxx/PHR/A
7.3 Record the pH of all solutions checked in daily pH log book.

8.0 DOCUMENTATION :
8.1 F:Sxxxx/PHR/A pH Meter calibration record
8.2 F:Sxxxx/DPHR/A Daily pH checking record.