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)
“The truth is, the whole administration under Roosevelt was demoralized by the system of dealing directly with subordinates. It was obviated in the State Department and the War Department under [Secretary of State Elihu] Root and me [Taft was the Secretary of War], because we simply ignored the interference and went on as we chose.... The subordinates gained nothing by his assumption of authority, but it was not so in the other departments.”
—William Howard Taft (1857–1930)