Lamotte SMART3 Colorimeter User Manual download pdf (Page 144)

APPLICATION: Domestic and industrial wastes.

RANGE: 0–1500 mg/L COD

MDL: 40 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, a green complex is formed. The

concentration of the green complex is measured at

605 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 H

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

per ppm NO

–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.

When scanning samples in 16 mm tubes, such as

COD, the sample chamber lid can not be closed. Use

the COD adapter to minimize stray light interference.

To further reduce stray light interference, do not scan

sample in direct sunlight.

COD, Standard Range SMART3 Test Procedures 11.10

Test Procedures

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Lamotte SMART3 Colorimeter User Manual Page 144