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Chapter A6. Field Measurements

National Field Manual for the Collection of Water-Quality Data (TWRI Book 9)

6.5 Reduction Oxidation Potential (Electrode Method)

By D.K. Nordstrom and F.D. Wilde

This section of Chapter 6 is available as a pdf file:
6.5, Version 1.2 (dated 9/2005) [265KB PDF]

Download a copy of Adobe Acrobat Reader for free.

Abstract

Reduction-oxidation (redox) potential -- also referred to as Eh -- is a measure of the equilibrium potential, relative to the standard hydrogen electrode, developed at the interface between a noble metal electrode and an aqueous solution containing electroactive chemical species. Measurements of Eh are used to evaluate geochemical speciation models, and Eh data can provide insights on the evolution and status of water chemistry in an aqueous system. Nevertheless, the measurement is fraught with inherent interferences and limitations that must be understood and considered to determine applicability to the aqueous system being studied. For this reason, Eh determination is not one of the field parameters routinely measured by the U.S. Geological Survey (USGS). This section of the National Field Manual (NFM) describes the equipment and procedures needed to measure Eh in water using a platinum electrode. Guidance as to the limitations and interpretation of Eh measurement also is included.

Contents

6.5 Reduction-oxidation potential

6.5.1 Equipment and supplies

6.5.1.A Electrode selection

6.5.1.B ZoBell's solution

6.5.1.C Equipment maintenance

6.5.2 Equipment test procedure

6.5.3 Measurement

6.5.3.A Interferences and limitations

6.5.3.B Interpretation

6.5.4 Troubleshooting

6.5.5 Reporting

Selected references

Return to Chapter A6 Contents Page

Return to Field Manual Table of Contents

Section 6.5 Archived Versions:

• Archive: 6.5, Version dated 4/1998 (370KB PDF)