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.
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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 25oC.
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.
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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 25oC)
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 120oC 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
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of carbon dioxide. 5.4.4 Solution D: Preparation of Saturated solution of Calcium hydroxide at 25oC (pH 12.45). Shake an excess of calcium hydroxide with water and decant at 25oC 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
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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.
6.0 ABBREVIATIONS
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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
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