Test Procedures
APPLICATION:
Domestic and industrial wastes.
RANGE:
0–150 mg/L COD
MDL:
5 mg/L
METHOD:
Dichromate in the presence of silver salts, at high
temperature in a closed system, oxidizes most organic
compounds to 95-100% of the theoretical amount. This
process is called digestion. As dichromate oxidizes the
organic compounds, the amount of yellow color is reduced.
The remaining yellow color is measured colorimetrically at the
420 nm and is directly proportional to the COD of the sample.
SAMPLE HANDLING &
PRESERVATION:
Collect samples in glass and test as soon as possible. If
samples must be stored, preservation is accomplished by
the addition of concentrated H2SO4 to adjust the pH below 2.
Samples with suspended solids should be homogenized in a
blender (100 mL for 30 seconds) and then stirred gently with
a magnetic stirrer.
INTERFERENCES:
Volatile organic compounds are not oxidized to the extent
that they are in the vapor above the digestion solution.
Therefore, they do not contribute to the COD reading. Chloride
concentrations above 10% of COD interfere with the mercury
free tubes. Chloride above 2000 ppm will interfere with the
mercury tubes. Nitrite gives a positive interference of 1.1
ppm O
2
per ppm NO
2
–N which is insignifi cant unless nitrite
concentrations are very high. Other reduced inorganic
compounds are stoichiometrically oxidized, causing a positive
interference. Corrections can be made for these compounds
based upon their stoichiometry and concentrations.
COD
, LOW RANGE
SMART Spectro 2 Test Procedures 05.02.16
www.
GlobalScientificSupply
.com
GLOBAL SCIENTIFIC SUPPLY
The Laboratory Supply Company!
