LaMotte SMART Spectro Spectrophotometer - Manual (Page 111)

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
insignificant 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–Standard Range 2/4 SMART SPECTRO TEST PROCEDURES 03.05