The aromatic spin trap 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS) is an efficient nitric oxide scavenger that has the potential to be employed for the control of NOX emissions from industrial processes. In the present study, we examined the in situ reaction of DBNBS with nitric oxide (NO), generated via the reduction of nitrite under acidic conditions at room temperature. Significant quantities of N-2 were detected during the reaction using the membrane inlet mass spectrometer (MIMS), Which suggested the homolytic cleavage of the C-N bond of a diazenyl radical, formed by decomposition of a DBNBS-NO adduct is a key reaction step which occurs during trapping. Measurements by nanostructured assisted laser desorption ionization mass spectrometer (NALDI-MS) established that the primary product from the reaction was 3,4,5-trinitrobenzene sulfonate, with a molecular Weight of 291.880 amu. The technique also disclosed the formation of other nitrobenzene products. The results obtained in the present study provide evidence of a new, competing reaction pathway occurring in the presence of added nitrite, whereby a nitro group is introduced in the aromatic system by coupling with a phenyl radical to yield a radical anion, which reacts readily with the electrophile N2O3, also present in the system.