We have experimented with three different methods for measuring nitrate levels in water samples with the colorimeter:
- Hach NitraVer5 reagent
- API test kit
- Nitrate reductase method
The first step in measuring nitrate levels in water is reduction (chemically or enzymatically) of nitrate (NO3) to nitrite (NO2). Methods 1 & 2 listed above use cadmium-reduction (APHA Standard Method ) wheras method 3 uses a plant enzyme, Nitrate reductase. All 3 assays measure nitrite levels with the Greiss test as the final colorimetric assay step.
Of these three methods tested so far, we prefer to use the Hach NitraVer5 reagent. Although it does use the cadmium-reduction method, it is easier to use than the enzyme assay and is more reproducible than the API test kit in our experience.