The nitrated lipids 9-nitro-oleic acid (9-NO(2)-OA) and 10-nitro-oleic acid (10-NO(2)-OA) have been reported to be present in blood of healthy humans. Free and esterified forms of 9-NO(2)-OA and 10-NO(2)-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-NO(2)-OA and 10-NO(2)-OA may interfere with the analysis of circulating nitrite and nitrate. In the present study, we investigated a possible interference of 9-NO(2)-OA and 10-NO(2)-OA with the GC-MS method of analysis of nitrite and nitrate involving derivatization by pentafluorobenzyl (PFB) bromide in aqueous acetone at 50 degrees C for 5 min (nitrite) or for 60 min (nitrite and nitrate). Our results show that 9-NO(2)-OA and 10-NO(2)-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 microM. Thus, nitrated lipids such as 9-NO(2)-OA and 10-NO(2)-OA can be excluded as potential interfering substances in the GC-MS quantitative determination of nitrite and nitrate as their PFB derivatives.