Preconcentration of Nitroalkanes with Archetype Metal-Organic Frameworks (MOFs) as Concept for a Sensitive Sensing of Explosives in the Gas Phase

Thermal desorption based enrichment is a general concept that can enhance any detection system's sensitivity and selectivity. Given their large interior surface area and chemical versatility, archetype metal-organic frameworks (MOFs) are selected for preconcentration of explosives and their precursors occurring in low concentrations, and are compared to the state-of-the-art sorbent Tenax TA. Applying inverse gas chromatography (iGC), this study shows that several archetype MOFs, namely HKUST-1 and MIL-53, surpass Tenax regarding their specific retention volume for nitromethane, a typical ingredient in improvised explosives. Using linear hydrocarbons as reference probe molecules, the dispersive surface energy is determined for all MOFs along with the specific contribution of the nitro group for HKUST-1 and ZIF-8. Trends from pulse-chromatographic iGC-investigations are mostly followed in breakthrough and thermal desorption experiments using a 1000 ppm nitromethane source. In these experiments, HKUST-1 proves the peak substance, with enrichment factors being 109-fold higher than for Tenax, followed by MIL-53. In case of HKUST-1, this factor is successfully reproduced for a 1 ppm concentration scenario. This shows that archetype MOFs can be suitable or even superior candidates for a sensitive sensing of nitroalkane explosives from the gas phase by a concept of preconcentration.