This test method covers the apparatus and procedure for the electrometric measurement of oxidation-reduction potential (ORP) in water. The test method described has been designed for the routine and process measurement of oxidation-reduction potential. ORP is defined as the electromotive force between a noble metal electrode and a reference electrode when immersed in a solution.  The ORP electrodes are inert and measure the ratio of the activities of the oxidized to the reduced species present. In addition, the ORP electrodes reliably measure ORP in nearly all aqueous solutions and in general are not subject to solution interference from color, turbidity, colloidal matter, and suspended matter. The apparatus to be used in the measurement of ORP includes: pH meter, reference electrode, oxidation-reduction electrode and electrode assembly. Materials necessary in the procedure for ORP measurement include chemical reagents, aqua regia, water, buffer standard salts, phthalate reference buffer solution, phosphate reference buffer solution, chromic acid cleaning solution, detergent, nitric acid, redox standard solution or ferrous-ferric reference solution, and redox reference quinhydrone solutions.

1.1 This test method covers the apparatus and procedure for the electrometric measurement of oxidation-reduction potential (ORP) in water. It does not deal with the manner in which the solutions are prepared, the theoretical interpretation of the oxidation-reduction potential, or the establishment of a standard oxidation-reduction potential for any given system. The test method described has been designed for the routine and process measurement of oxidation-reduction potential.

1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.