Calibration of pH meter

1.0    PURPOSE: 

            1.1     To lay down the procedure for Calibration of pH Meter. 

2.0    SCOPE

2.1    This procedure is applicable for Calibration of pH meters located in the Quality control.

3.0    RESPONSIBILITY

3.1    Assistant.-QC

4.0    ACCOUNTABILITY

4.1     Sr.Executive-QC

5.0    PROCEDURE

5.1    Preparation of Buffers 

5.1.1    Potassium tetraoxalate, 0.05m: 
    Dissolve 12.61g of KH3 (C2O4)2.2H2O in water to make 1000mL.
5.1.2    Potassium biphthalate, 0.05m:
    Dissolve 10.12g of KHC8H4O4 , previously dried at 1100C for 1 
    hour, in water to make 1000mL.
5.1.3    Equimolal phosphate, 0.05m:
    Dissolve 3.53g of Na2HPO4 and 3.39g of KH2PO4, each previously
    dried at 1200C for 2 hours, in water to make 1000mL.
5.1.4    Sodium Tetraborate, 0.01m:
    Dissolve 3.80g of Na2B4O7.10H2O in water to make     1000mL.Protect from absorption of carbon dioxide.
5.1.5    Calcium Hydroxide, Saturated at 25° C: Shake an excess of Calcium Hydroxide with water and decant at 25° C before use. Protect from absorption of carbon dioxide.
    
    Note: Buffer solutions of greater volumes shall be prepared using proportionate quantities.

5.2    Usage of pH buffers:

5.2.1    The prepared buffer stock solutions shall be stored in amber colored glass bottles, kept in refrigerator and used with in three months from the date of preparation.
5.2.2    Buffers for routine use shall be transferred from stock solution to sample bottles and used with in one week from the date of dispensing.

Note: The buffer solution (stock or routine use) shall be discarded when microbial growth or precipitation is observed.

5.3    Buffers and pH Values at Different Temperatures 

5.3.1    Buffers prepared as above have pH values as included in the following table:

pH  values of buffer solutions for Calibration

5.3.2    The pH meter shall be standardized using buffers prepared as directed under 5.1 
5.3.2.1    To standardize the pH meter select two buffer solutions  
                       whose difference in pH does not exceed 4 units and such 
                       that the expected pH of the material under test falls 
                                                between them.
5.3.2.2    Maintain the temperatures of both buffer solutions within  
                                                200C-350C.
5.4    Calibration 
        Manual calibration:
5.4.1    Operate the pH meter as per the respective SOP.
5.4.2    Fill the cell with one of the buffer solutions for Calibration.                             
5.4.3    Set the “temperature” control at the temperature of the solution and adjust the calibration control to make the observed pH value identical with that tabulated. 
5.4.4    Rinse the electrodes and cell with several portions of the second buffer for Calibration, then fill the cell with it. 
5.4.5    The pH of the second buffer shall be within +0.07 of the tabulated value.
5.4.6    Adjust the “slope” control to make the observed pH value identical with that tabulated. Repeat the Calibration until both buffer solutions give pH values within + 0.02 pH units of the tabulated value without further adjustment of the controls.
Auto  calibration:
5.4.7    Operate the pH meter as per the respective SOP.
5.4.8    Fill the cell with one of the buffer solutions for Calibration.      
5.4.9    Enter the pH value of the buffer solution filled and wait of stabilization.                       
5.4.10    Rinse the electrodes and cell with several portions of the second buffer for Calibration, then fill the cell with it
5.4.11    Enter the pH value of the second calibration solution and wait for stabilization
5.4.12    Read the pH of the respective calibrated solutions and the buffer solutions should give pH values within + 0.02 pH units.
5.4.13    Record the Calibration details as per Format No.QC704-F01.
    
5.5    Frequency

5.5.1    Daily in morning hours or whenever required after. 

Ph meter, linearity, coefficient, concentration, quality control lab