1.0 PROCEDURE
Note: Use Carbon dioxide free water.
Reagents:
(1) Potassium Tetra oxalate, 0.05 M (pH 1.68 at 25°C): Dissolve 3.1525 g of KH3(C2O4)2. 2H2O in purified water to make 250 mL.
(2) Potassium Biphthalate, 0.05 M (pH 4.01 at 25°C): Dissolve 2.5300 g of KHC8H4O4, previously dried at 110°C for 1 hour, in purified water to make 250 mL.
(3) Equimolal Phosphate, 0.05 M (pH 6.86 at 25°C): Dissolve 0.8825 g of anhydrous disodium hydrogen phosphate (Na2HPO4) and 0.8475 g of potassium dihydrogen phosphate (KH2PO4), each previously dried at 120°C for 2 hours, in purified water to make 250 mL.
(4) Sodium Tetraborate, 0.01M (pH 9.18 at 25°C): Dissolve 0.9500 g of Na2B4O7.10H2O in purified water to make 250 mL. Protect from absorption of carbon dioxide.
(5) Calcium Hydroxide, saturated (pH 12.45 at 25°C) : Shake the excess of calcium hydroxide with purified water and decant at 25°C before use. Protect from absorption of carbon dioxide.
Procedure :
(1) Operate and calibrate the pH meter and electrode system according to the SOP for the pH meter.
(2) All measurements should be made at the same temperature of 25°C ± 2°C unless otherwise stated in the testing procedure in the monograph.
Note : To standardize the pH meter, select two Buffer Solutions for Standardization whose difference in pH does not exceed 4 units and such that the expected pH of the sample under test falls between them.
pH Values of Buffer Solutions for Standardization
Standardization, general testing procedure, potassium dihydrogen
