Optimization of the electrochemical reduction of nitromethane for the development of an integrated portable sensor

During the past ten years, the use of artisanal explosive compositions in terrorism attacks has increased and efficient detectors are greatly needed. Nitromethane is an interesting target for detection due to its uses in artisanal explosive compositions and also for its carcinogenic characteristics. Several techniques including electrochemistry have been developed but require laboratory equipment, preparative steps or complex working electrodes. We here describe the development of a robust, simple and commercially available electrochemical detection system. Square wave voltammetry was used for this purpose with a gold working electrode and a phosphate buffer at pH 7.5. The limits of detection (LOD) were 2.3 μM without dissolved oxygen in the solution and 12.5 μM in air. Furthermore, a mechanistic investigation enabled us to confirm, under these conditions, a 4-electron reduction mechanism from nitromethane to N-methylhydroxylamine. However, under real conditions of use, N-methylhydroxylamine is not the sole product of the reduction reaction. Other products have been identified by nuclear magnetic resonance characterization and a reaction scheme was established. The system could be minimized for on-site measurements by using screen-printed electrodes with a portable potentiostat. A vapor concentration of 20 ppm of nitromethane could be detected within 1 min thanks to this electrochemical sensing system.