Reagents:

Calibrate the electrode system against standard buffer solutions of called pH: Buffer tablets that having pH 4.0, 7.0 and 9.2 which are commercially available. Since buffer solutions may deteriorate as a result of mold contamination or growth, prepare fresh as needed. Instead buffer solutions can also be prepared as following:

pH 4 buffer solution : This Dissolve 10.2 gm anhydrous potassium biphthalate (KHC₈H₄) using boiled and cooled distilled water. Dilute to 1 dm³.

pH 7 buffer solution: This Dissolve 1.361 gm anhydrous potassium dihydrogen phosphate (KH₂PO₄), and 1.42 gm anhydrous disodium hydrogen phosphate, Na₂HPO₄ both of that have been dried at 110ºC to 130ºC. Use distilled water that have been cooled and boiled. Dilute to 1 dm³.

pH 9.2 buffer solution : This Dissolve: 3.81 gm borax (Na₂B4O₇ 10H₂O) in distilled water. The Dilute to 1 dm³.