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.

  1. So, 22.6% of the 30 mg/L nitrate is nitrogen.
  2. 0.226 N x 30 mg/L nitrate = 6.78 mg/L N.
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22.6% of the 30 mg/L nitrate is nitrogen.
An animation showing that 22.6% of the 30 mg/L nitrate is nitrogen.
0.226 x 30mg/L = 6.78 mg/L N
An animation showing that 0.226 N multiplied by 30 mg/L nitrate equals 6.78 mg/L N.

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