EPA Standards Example
If a water sample contains 30 mg/L nitrate, NO3-, does it exceed the EPA recommendation of 10 mg/L nitrate nitrogen, NO3-–N ?
At first glance, it may appear that it does, but remember that the notation NO3--N refers to nitrogen that comes from nitrate. It is not the same as the chemical formula NO3-, which refers to the molecule containing both nitrogen and oxygen.
We know from building nitrate on the previous page that nitrate contains 22.6% nitrogen.