Abstract <p>Processes of the chromatographic separation and the formation of negative ion (<b>NI</b>) mass spectra are studied by gas chromatography–mass spectrometry (<b>GC–MS</b>) in the resonance electron capture mode, implemented with the minimal technical modification of the domestic serial GC–MS Chromatec-Crystal complex, and a comparison with the basic positive ion (<b>PI</b>) mode upon electron ionization is made. It is found that the chromatographic retention time for isomers increases in direct proportion to the dipole moment of their molecules, illustrating the importance of intermolecular dipole interactions between the polar molecules of the analyte and the stationary phase. It is shown that the chromatograms by the total current of the NI recorded with the fast continuous scanning by the energy of ionizing electrons in the low-energy range 0–10 eV reflect well the component composition of the analyzed sample, and the integral mass spectra of the NI are characteristic of and selective for isomers, and are complementary in information content to the standard PI mass spectra. This is due to the predominance of nitro–nitrite rearrangements and the simple cleavage of the C–NO₂ bond during negative ion formation over H-shift reactions, dominating in the formation of PI from TNT isomers.</p>