Cell Biolabs’ OxiSelect™ Nitric Oxide (Nitrite/Nitrate) Assay Kit is a simple, colorimetric assay that quantitatively measures NO in various samples by NO2-/NO3- determination. First, the nitrate (NO3-) in the sample is converted to nitrite (NO2-) by nitrate reductase enzyme. Next, total nitrite is detected with Griess Reagents as a colored azo dye product (absorbance 540 nm). Each kit provides sufficient reagents to perform up to 100 assays using a 96-well microtiter plate format, including blanks, standards and unknown samples. The kit is suitable for serum, plasma, urine, saliva, lysates, and media (see Preparation of Samples) with detection sensitivity limit of ~ 2 µM (in 50 µL sample volume).