A system and a process for measuring, by glow discharge spectrometry, the elemental and/or molecular chemical composition of an organic solid sample (10). The sample (10) is positioned so as to seal a glow discharge plasma reactor (2), a gaseous mixture including at least one inert gas and gaseous oxygen is injected into the reactor (2), the concentration of gaseous oxygen being between 0.1% and 15% by weight of the gaseous mixture, an electric discharge of radiofrequency type is applied to the electrodes of the plasma reactor (2) in order to generate a glow discharge plasma, and the solid sample (10) is exposed to the plasma so as to etch an erosion crater in the solid sample (10); at least one signal representative of an ionized species of negative charge is selected and measured using a mass spectrometer (4).