SOP for Calibration of pH Meters

1.0 OBJECTIVE

To calibrate the equipment for reliable and accurate results.

2.0 SCOPE

This procedure is applicable for pH meters installed at Quality control laboratory.

3.0 RESPONSIBILITY

3.1 Doing: Technical Assistant
3.2 Checking: Executive /Manager

4.0 ACCOUNTABILITY

Head of the Department

5.0  PROCEDURE

5.1 Operate the instrument as per respective Standard Operating Procedure.
5.2 Use Certified Standard pH buffer to set the instrument at pH 7.00 (with 7.00 pH buffer) and pH 4.00 (with 4.00 pH buffer) at 25^oC.
5.3 Take 100 ml buffer pH 4.0 & pH 7.0 from the Certified buffer bottle in a glass bottle. Discard the Standard pH buffer after one month.
5.4 Prepare different pH solutions of 0.05 M Potassium biphthalate, 0.05 M equimolol phosphate, 0.01 M sodium tetraborate and Calcium Hydroxide (saturated solution at 25^oC)
5.4.1 Solution A: Preparation of 0.05 M Potassium Biphthalate (pH 4.01)

Dissolve 10.12 gm. of KHC₈H₄O₄ ( previously dried at 110 ^oC for 1 hour) in water to make 1000 ml.

5.4.2 Solution B: Preparation of 0.05 M equimolol phosphate buffer( pH 6.86)

Dissolve 3.53 gm. of Na₂HPO₄ and 3.39 gm. of KH₂PO₄ (each previously dried at 120^oC for 2 hour) in water to make 1000 ml.

5.4.3 Solution C: Preparation of 0.01 M Sodium tetraboarte buffer( pH 9.18)

Dissolve 3.80 gm.of Na₂B₄O₇.10 H₂O in water to make 1000 ml. Protect the solution from absorption 

of carbon dioxide. 5.4.4 Solution D: Preparation of Saturated solution of Calcium hydroxide at 25^oC (pH 12.45).  Shake an excess of calcium hydroxide with water and decant at 25^oC before use. Protect the solution from absorption of carbon dioxide. (Prepare fresh solution when required)
5.5 Check the pH of above buffer solutions. It should be within + 0.07. Record the value in the prescribed Annexure-II 5.6 Check the pH of Certified buffer pH 4.0 & pH 7.0. It should be within +0.02 pH limit of labelled value. Record the value as per Annexure-II
5.7 Discard buffer solution A, B and C after three months.
5.8 Frequency of calibration:- 15 days.
5.9 Daily calibration
5.9.1 Repeat the same procedure for daily calibration of pH meter using solution A, B and solution C and record value as per annexure-I
5.10 If it is out of specified limit, follow the S.O.P.

Related: Principle and Working of pH Probes

6.0 ABBREVIATIONS

6.1 ^oC = Degree centigrade
6.2 Na₂B₄O₇.10H₂O = Sodium Tetraborate Decahydrate
6.3 U.S.P. = United state pharmacopoeia

6.4 Na₂HPO₄ = Disodium hydrogen orthophosphate
6.5 KH₂PO₄  = Potassium dihydrogen orthophosphate
6.6 gms. = Grams
6.7 S.O.P.No. = Standard operating procedure number
6.8 KHC₈H₄O₄  = Potassium Biphthalate

ANNEXURE-I

Q. C. Department

 DAILY CALIBRATION RECORD

Name of  the Instrument     :  pH METER

Make                                                :  

Model  No                                      :                                  

IDENTIFICATION NO.                    :

 ______________________________________________________________________________

Primary standard : Certified  buffer (pH 4.00 &pH 7.00)

OBSERVATION CHART

Date	0.05 M Potassium Biphthalate ( 4.01+ 0.07)	0.05 M equimolol phosphate ( 6.86+ 0.07)	0.01 M  sodium        Tetraborate ( 9.18+ 0.07)	Check point ( if applicable)	Calibrated by	Checked by

ANNEXURE-II

Q. C. Department

  CALIBRATION RECORD OF pH METER

Name of  the Instrument    :  pH METER

Make                                                :  

Model  No                                     :                                     

IDENTIFICATION NO.                   :

 _______________________________________________________________________________

Primary standard : Certified  buffer Primary standard : Certified  buffer (pH 4.00 & pH 7.00)

Batch No:___________ (pH 7.00)

Batch No.:__________ (pH 4.00)

OBSERVATION : 

Buffer	Theoretical pH Value(At 25oC)	Observed value	Tolerance	Remarks
0.05 M Potassium Biphthalate	4.01		+ 0.07
0.05 M equimolol phosphate	6.86		+ 0.07
0.01  M sodium Tetraboarte	9.18		+ 0.07
Calcium hydroxide (saturated)	12.45		+ 0.07
Standard  Certified buffer	6.98		+ 0.02
Standard Certified buffer	4.01		+ 0.02

Remarks                              :

Calibration date                   :                                                                     

Calibration due date            :

Calibrated  by                     :
Checked  by                       :

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