NEMI Method Summary

Method Summary Information

Method Number: 5220D Media: WATER
Revision: Standard Methods Online
Method Source: Standard Methods
Subcategory: ORGANIC Analytes in this method
Official Name: Closed Reflux, Colorimetric Method
Descriptive Name Chemical Oxygen Demand
Source Info: Standard Methods Online is jointly produced by the American Public Health Association (APHA), the American Water Works Association (AWWA), and the Water Environment Federation (WEF).
These organizations may be contacted by phone for more information on Standard Methods Online:
APHA: (301) 893-1894
AWWA: (800) 926-7337, (1-303-794-7711, outside U.S. / Canada)
WEF: (800) 666-0206 (1-703-684-2452 outside U.S. / Canada)
Citation: Standard Methods Online
 
Brief Method
Summary:
 When a sample is digested, the dichromate ion oxidizes COD material in the sample. This results in the change of chromium from the hexavalent (VI) state to the trivalent (III) state. Both of these chromium species are colored and absorb in the visible region of the spectrum. The dichromate ion absorbs strongly in the 400-nm region, where the chromic ion absorption is much less. The chromic ion absorbs strongly in the 600-nm region, where the dichromate has nearly zero absorption.
Scope And
Application:
 This method determines the COD of water samples.
Applicable
Conc Range:
 > 50 mg O2/L
Interferences: The most common interferent is the chloride ion. Chloride reacts with silver ion to precipitate silver chloride, and thus inhibits the catalytic activity of silver.
QC Requirements:
Sample Handling: Preferably collect samples in glass bottles. Test unstable samples without delay. If delay before analysis is unavoidable, preserve sample by acidification to pH less than or equal to 2 using conc sulfuric acid.
Blend (homogenize) all samples containing suspended solids before analysis.
Max Holding Time:
 28 days at 4oC
 
Relative Cost: Less than $50
URL to obtain ordering information for this method:
http://www.standardmethods.org/
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