ASTM: D1498: Redox Potential of Water
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Official Method Name
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Standard Practice for Oxidation-Reduction Potential of Water |
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Current Revision
| ASTM D1498-14(2022)e1, approved December 7, 2022. |
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Media
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WATER |
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Instrumentation
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Not Applicable |
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Method Subcategory
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Physical |
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Method Source
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Citation
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Brief Method Summary
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This is a practice designed to measure the ORP which is defined as the electromotive force between a noble metal electrode and a reference electrode when immersed in a solution. The practice describes the equipment available to make the measurement, the standardization of the equipment and the procedure to measure ORP. The ORP electrodes are inert and measure the ratio of the activities of the oxidized to the reduced species present. |
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Scope and Application
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This practice 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 practice described has been designed for the routine and process measurement of oxidation-reduction potential. |
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Applicable Concentration Range
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Interferences
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The ORP electrodes reliably measured ORP in nearly all aqueous solutions and in general are not subject to solution interference from color, turbidity, colloidal matter, and suspended matter. The ORP of an aqueous solution is sensitive to change in temperature of the solution, but temperature correction is rarely done due to its minimal effect and complex reactions. Temperature corrections are usually applied only when it is desired to relate the ORP to the activity of an ion in the solutions. The ORP of an aqueous solution is almost always sensitive to pH variations even to reactions that do not appear to involve hydrogen or hydroxyl ions. The ORP generally tends to increase with an increase in hydrogen ions and to decrease with an increase in hydroxyl ions during such reactions. Reproducible oxidation-reduction potentials cannot be obtained for chemical systems that are not reversible. Most natural and ground waters do not contain reversible systems, or may contain systems that are shifted by the presence of air. If the metallic portion of the ORP electrode is sponge-like, materials absorbed from solutions may not be washed away, even by repeated rinsings. In such cases, the electrode may exhibit a memory effect. The ORP resulting from interactions among several chemical systems present in mixed solutions may not be assignable to any single chemical. |
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Quality Control Requirements
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Sample Handling
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Collect the samples in accordance with Practices D 3370. |
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Maximum Holding Time
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Relative Cost
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Unknown |
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Sample Preparation Methods
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