Abstract Aromatic nitro compounds are quantitatively converted to the corresponding anion-radical form by electron tranfer at the surface of thermally activated magnesium oxide. The radicals are stable in the absorbed state, and the reaction is useful for the identification and determination of the parent compound. The method is applied to detect and quantify various nitrobenzenes, nitrotoluenes and teryl by electron spin resonance spectrometry. For 2,4,6-trinitrotoluene (TNT), the detection limit was ca. 10 ng; the r.s.d. at the 2 μg level was ± 1.8%. The analysis of hand-swab extracts that contained TNT at the trace levels demonstrateds a potentially important application of the method.