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 abundance. 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 TNTH-. 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-.