9- and 10-Nitro-oleic acid do not interfere with the GC–MS quantitative determination of nitrite and nitrate in biological fluids when measured as their pentafluorobenzyl derivatives

The nitrated lipids 9-nitro-oleic acid (9-NO2-OA) and 10-nitro-oleic acid (10-NO2-OA) have been reported to be present in blood of healthy humans. Free and esterified forms of 9-NO2-OA and 10-NO2-OA have been detected in human plasma at about 600 and 300 nM, respectively. These concentrations are of the same order of magnitude of circulating nitrite. In theory, 9-NO2-OA and 10-NO2-OA may interfere with the analysis of circulating nitrite and nitrate. In the present study, we investigated a possible interference of 9-NO2-OA and 10-NO2-OA with the GC–MS method of analysis of nitrite and nitrate involving derivatization by pentafluorobenzyl (PFB) bromide in aqueous acetone at 50 °C for 5 min (nitrite) or for 60 min (nitrite and nitrate). Our results show that 9-NO2-OA and 10-NO2-OA do not interfere with the GC–MS analysis of nitrite and nitrate as PFB derivatives in plasma and phosphate buffered saline when added to these matrices at supraphysiological concentrations of 1–10 μM. Thus, nitrated lipids such as 9-NO2-OA and 10-NO2-OA can be excluded as potential interfering substances in the GC–MS quantitative determination of nitrite and nitrate as their PFB derivatives.