Inorganic Interference
Some samples of water contain high levels of oxidizable inorganic materials which may interfere with the determination of COD. Because of its high concentration in most wastewater, chloride is often the most serious source of interference. Its reaction with potassium dichromate follows the equation:
Prior to the addition of other reagents, mercuric sulfate can be added to the sample to eliminate chloride interference.
The following table lists a number of other inorganic substances that may cause interference. The table also lists chemicals that may be used to eliminate such interference, and the compounds formed when the inorganic molecule is eliminated.
| Inorganic molecule | Eliminated by | Elimination forms |
|---|---|---|
| Chloride | Mercuric sulfate | Mercuric chloride complex |
| Nitrite | Sulfamic acid | N2 gas |
| Ferrous iron | - | - |
| Sulfides | - | - |
Read more about this topic: Chemical Oxygen Demand
Famous quotes containing the words inorganic and/or interference:
“Man, unlike anything organic or inorganic in the universe, grows beyond his work, walks up the stairs of his concepts, emerges ahead of his accomplishments.”
—John Steinbeck (1902–1968)
“Adolescent girls were fighting a mother’s interference because they wanted her to acknowledge their independence. Whatever resentment they had was not towards a mother’s excessive concern, or even excessive control, but towards her inability to see, and appreciate, their maturing identity.”
—Terri Apter (20th century)