Optimisation of the measurement of nitrite and nitrate in serum by the Griess reaction

Nitrite (NO2-) and nitrate (NO3-) concentrations are usually measured as a marker of NO metabolism. Indeed, this radical plays an important role in a lot of pathological processes. The aim of this study was to validate and standardize a method for the quantification of these two metabolites in serum. The most commonly method involved to determine nitrite and nitrate is the Griess reaction. From the different methods which are reported in literature, we tested several parameters to define operating conditions: the samples were deproteinized with zinc sulfate and reduced with cadmium granules. Analytical recovery of NO3- added to serum samples after reduction was 99.6% +/- 3.2% (n = 4). Within-run precision was 6.1% (n = 17) and between day precision was 6.6% (n = 12). Usual values were determined from healthy fasted subjects: the mean concentration of NO2- and NO3- was 47.8 muM +/- 15.7 muM (n = 25). The detection limit of the assay was 1.3 muM and the quantitation limit was 2.5 muM. We tested also an HPLC method. However, it was not possible to use it from a biological matrice.