Water Resources--Office of Water Quality

National Field Manual

6.5 REDUCTION-OXIDATION POTENTIAL (ELECTRODE METHOD)

Version 1.2, dated 9/2005 (262 kb pdf)

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 - pH

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

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

Maintainer: Office of Water Quality
Last Modified: 20Jun06 imc
Archive of Section 6.5, dated 4/1998