A hydride Meisenheimer complex of 2,4,6-trinitrotoluene (TNT) (TNTH) was synthesized using tetramethylammonium octahydroborate. TNT and TNTH (as the tetramethylammonium salt) were analyzed by direct exposure probe mass spectrometry using electron impact (EI), chemical ionization (CI) and negative-ion chemical ionization (NCI). For further identification, the ions of the mass spectra were investigated using tandem mass spectrometry with collision-induced dissociation (CID). Although the EI mass spectra of both compounds were similar, the CID mass spectra of the ions at m/z 227 (M+ of TNT) of the two compounds showed large differences in daughter ion abundances. A major difference between the two compounds also appeared in their CI methane mass spectra. Two abundant ions, at m/z 183 and 198, appeared only in the CI mass spectrum of TNNH. CID parent ion scans showed that the origin of these two ions was not the m/z 227 ion. We suggest that these ions are formed by chemical reactions of the complex on the surface of the heated probe tip, followed by ionization. These reactions, probably a reduction process forming m/z 198 and hydrolysis forming m/z 183, occur preferentially in TNTH, the already reduced form of TNT. Formation of the ions at m/z 183 and 198 was also observed in the liquid chromatography particle beam CI mass spectrum of TNTH.