Determination of oxidation-reduction potential (Electrometric method)
1 General provisions
1.1 Subject matter
This standard specifies the determination of oxidation-reduction potential in water by electrometric method.
1.2 Scope
This method is applicable to the determination of oxidation-reduction potential of natural water.
2 Principle
Oxidation-reduction in water is usually represented by oxidation-reduction potential (Eh). When platinum electrode and reference electrode are inserted into aqueous solution, an electron transfer reaction will occur on metal surface, generating potential difference between electrode and solution. When the electrode reaction reaches equilibrium, the potential difference relative to hydrogen standard electrode is called oxidation-reduction potential.
3 Apparatus
3.1 Potentiometer or general acidimeter: accurate to ± 0.1 mV.
3.2 Platinum electrode.
3.3 Saturated calomel electrode.
3.4 Thermometer: accurate to ± 0.5°C.
3.5 Volumetric flask: 1,000 mL.
3.6 Common test equipment.
4 Reagents
4.1 Potassium hydrogen phthalate buffer (pH=4.00, 25 °C): Dissolve 10.12 g of potassium hydrogen phthalate (KHC8H4O4)in water and dilute it to 1,000 L.
4.2 Phosphate buffer (pH=6.86, 25 °C): Dissolve 3.39 g of potassium dihydrogen phosphate (KH2PO4) and 3.55 g of anhydrous disodium hydrogen phosphate (Na2HPO4) in water and dilute it to 1,000mL.
4.3 Oxidation-reduction standard solution: Select either of the following two standard solutions.
Foreword i
1 General provisions
2 Principle
3 Apparatus
4 Reagents
5 Procedure
6 Representation of results
