ASTM D1498-00
(Practice)Standard Practice for Oxidation-Reduction Potential of Water
Standard Practice for Oxidation-Reduction Potential of Water
SCOPE
1.1 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.
1.2 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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D 1498–00
Standard Practice for
1
Oxidation-Reduction Potential of Water
This standard is issued under the fixed designation D 1498; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope
R = gas constant,
T = absolute temperature, °C + 273.15,
1.1 Thispracticecoverstheapparatusandprocedureforthe
n = number of electrons involved in process
electrometric measurement of oxidation-reduction potential
reaction, and
(ORP) in water. It does not deal with the manner in which the
A and A = activities of the reactants in the process.
ox red
solutions are prepared, the theoretical interpretation of the
3.2 For definitions of other items used in this practice, refer
oxidation-reduction potential, or the establishment of a stan-
to Terminology D 1129.
dard oxidation-reduction potential for any given system. The
practice described has been designed for the routine and
4. Summary of Practice
process measurement of oxidation-reduction potential.
4.1 This is a practice designed to measure the ORPwhich is
1.2 This standard does not purport to address all of the
defined as the electromotive force between a noble metal
safety concerns, if any, associated with its use. It is the
electrode and a reference electrode when immersed in a
responsibility of the user of this standard to establish appro-
solution. The practice describes the equipment available to
priate safety and health practices and determine the applica-
make the measurement, the standardization of the equipment
bility of regulatory limitations prior to use.
and the procedure to measure ORP. The ORP electrodes are
2. Referenced Documents inert and measure the ratio of the activities of the oxidized to
the reduced species present.
2.1 ASTM Standards:
2
D 1129 Terminology Relating to Water
5. Significance and Use
2
D 1193 Specification for Reagent Water
5.1 ORP provides a useful measurement of the oxidizing or
D 3370 Practices for Sampling Water from Closed Con-
2
reducing nature of a particular water sample. ORP measure-
duits
ments are commonly made in water and wastewater samples.
3. Terminology 5.2 Various applications include monitoring the
chlordination/dechlorination process of water, recgonition of
3.1 Definitions of Terms Specific to This Standard:
oxidants/reductants present in wastewater, monitoring the
3.1.1 oxidation-reduction potential— the electromotive
cyclechemistryinpowerplants,andcontrollingtheprocessing
force, Em, developed between a noble metal electrode and a
of cyanide and chrome waste in metal plating baths.
standard reference electrode. This oxidation-reduction poten-
tial (ORP) is related to the solution composition by:
6. Interferences
RT
o
6.1 The ORPelectrodes reliably measured ORPin nearly all
E 5 E 1 2.3 log A / A
m ox red
nF
aqueous solutions and in general are not subject to solution
interference from color, turbidity, colloidal matter, and sus-
where:
pended matter.
E = ORP,
m
o
E = constant that depends on the choice of 6.2 The ORP of an aqueous solution is sensitive to change
reference electrodes. in temperature of the solution, but temperature correction is
F = Faraday constant, 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
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solutions.
This practice is under the jurisdiction of ASTM Committee D19 on Water and
is the direct responsibility of Subcommittee D19.03 on Sampling of Water and
6.3 The ORP of an aqueous solution is almost always
Water-Formed Deposits, Surveillance of Water, and Flow Measurement of Water.
sensitive to pH variations even to reactions that do not appear
Current edition approved May 10, 2000. Published December 2000. Originally
toinvolvehydrogenorhydroxylions.TheORPgenerallytends
published as D 1498 – 57 T. Last previous edition D 1498 –93.
2
Annual Book of ASTM Standards, Vol 11.01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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D 1498–00
TABLE 1 National Institute of Standards and Technology (NIST)
to increase with an increase in hydrogen ions and to decrease
Materials for Reference Buffer Solutions
with an increase in hydroxyl ions during such reactions.
NIST Standard
6.4 Reproducible oxidation-reduction potentials cannot be
Sample Buffer Salt Drying Procedure
obtained for chemical systems that are not reversible. Most
A
Designation
naturalandgroundwatersdonotcontainreversiblesystems,or
186-II-e disodium hydrogen phosphate 2 h in ov
...
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