PromoCell’s colorimetric Nitric Oxide Assay Kit I provides an accurate and convenient measurement of total nitrate/nitrite concentration in a simple two-step process. The first step is to convert nitrate to nitrite, utilizing nitrate reductase. The second step involves addition of the Griess Reagents which converts nitrite into a deep purple azo compound. Measurement of the absorbance of the azo chromophore accurately reflects nitric oxide amount in samples. The detection limit of the assay is approximately 0.1 nmole nitrite/well, or 1 μM.