My nitrate results are suddenly about 4 times what they usually are. What might be causing this?

Document ID

Document ID TE519

Version

Version 2.0

Status

Status Published

Published Date

Published Date 27/05/2017
Question
My nitrate results are suddenly about 4 times what they usually are. What might be causing this?
Summary
Nitrate results off by about 4x
Answer
This is likely due to the form of nitrate that is displayed on your Hach colorimeter or spectrophotometer. The default form is NO3-N, which is nitrate as nitrogen, and is a common way to report results to regulatory agencies. However, most Hach instruments can also display results as NO3. The same amount of color is measured in the test regardless of which form is used, but when this color is converted to concentration, different conversions are used for the different forms.

The conversion to mg/L NO3-N uses the molecular weight of nitrogen, whereas the conversion to mg/L NO3 uses the weight of nitrate, which is 4.427 times the weight of nitrogen. The options menu in the Nitrate program has a chemical form option that will allow you to change the displayed chemcial form.