Nitrite is measured with the standard Greiss test. In this test, sulfanilamide reagent is converted to a diazonium salt by nitrite (NO2) in the water sample. The diazonium salt is then reacted with NED (N-1-napthylethylene diamine dihydrochloride) reagent to form an azo dye which has a purple/magenta color that is measured at 520-550 nm (suitable for the colorimeter 528 nm green LED).
We have so far tested two methods for measuring nitrite levels in water samples with the colorimeter:
- Greiss assay - make your own reagents
- API test kit - commercial kit, reagents supplied
Of these two methods tested so far, the API test kit is more convenient for at-home use although we do also like to make our own reagents as well. Really depends on which is most convenient.