|
| Standard Methods |
| 5220D |
| Standard Methods Online |
| Descriptive Name: Chemical Oxygen Demand Official Name: Closed Reflux, Colorimetric Method |
| Media: WATER |
| Organic |
| Standard Methods Online - Standard Methods for the Examination of Water and Wastewater |
This is a proprietary method.
Please visit the method owner's site for method documentation |
| 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. |
| This method determines the COD of water samples. |
| > 50 mg O2/L |
| 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. |
| |
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. |
| 28 days at 4oC |
| Less than $50 |
| |
| |