New analytical methods have been developed and existing methods have been improved for the detection of explosives and their degradation products by increasing their sensitivity and selectivity. Some of the analytical methods available for detection of explosives and degradation products are gas chromatography, mass spectrometry, high performance liquid chromatography, and gas chromatography with mass spectrometry. This work presents the design and development of the experiments for the detection of the spectroscopic signature of TNT buried in sand and its degradation products. These experiments are conducted using a series of soil tanks with controlled environmental conditions such as: temperature, soil moisture content, relative humidity and radiation (UV and VIS). Gas chromatography and solid-liquid extraction with acetonitrile were used for the analysis of explosives. Sampling of tanks was performed in three points on the surface. The results show that TNT and 2,4-DNT are the main explosives that reach the surface of tanks. Temperature and water content play a most important role in the degradation and diffusion of TNT. Finally, the tanks were disassembled and sampling in deep with the objective to obtain a concentration profile. The results demonstrated that the highest concentration was located at 5 cm from surface.
Detection and removal of antipersonnel and antitank landmines is a great challenge and a worldwide enviromental and humanitarian problem. Sensors tuned on the spectroscopic signature of the chemicals released from mines are a potential solution. Enviromental factors (temperature, relative humidity, rainfall precipitation, wind, sun irradiation, pressure, etc.) as well as soil characteristics (water content, compaction, porosity, chemical composition, particle size distribution, topography, vegetation, etc), have a direct impact on the fate and transport of the chemicals released from landmines. Chemicals such as TNT, DNT and their degradation products, are semi-volatile, and somewhat soluble in water. Also, they may adsorb strongly to soil particles, and are susceptible to degradation by microorganisms, light, or chemical agents. Here we show an experimental procedure to quantify the effect of the above variables on the spectroscopic signature. A number of soil tanks under controlled conditions are used to study the effect of temperature, water content, relative humidity and light radiation.
The detection of trace amount of explosives is of utmost importance in many day-to-day military operations. Moreover, the detection of landmines is a complex and urgent worldwide problem, which needs specific, rapid and cost effective solutions. The most commonly used explosive in landmines is 2,4,6-trinitrotoluene (TNT). Almost 80% of the types of mines manufactured worldwide contain TNT. This contribution describes the use of Immersion Mode Solid-Phase Microextraction (I-SPME) for extraction of TNT and their degradation products from surface soil samples for subsequent analysis by either GC with 63Ni micro cell Electron Capture Detector or gas chromatograph-mass spectrometer coupled to a Tunable Electron Energy Monochromator. A pretreatment step was introduced for the soil samples which extracted the target compounds into an aqueous phase. The experimental results demonstrated the effects of controllable variables. Parameters studied include the chemical properties of the fiber coating, extraction and desorption times, fiber extraction and matrix effect. Surface soil samples containing TNT were evaluated to study the detection of the nitroaromatic explosives and its degradations products using different environmental conditions such as sample temperature, sample contact time and water content.
The detection of hidden explosives using vapors emanating from explosives has been considered an area in explosives technology that requires high sensitivity and selectivity. In this work is reported the results of two methods for vapor explosive detection, GC-μECD and GC/MS coupled to a Tunable Electron Energy Monochromator (TEEM-GC/MS). Both used Solid Phase Microextraction (SPME) in Headspace (HS) mode to collect vapors above the samples. Optimum parameters for SPME were determined with the purpose of obtaining a high-quality extraction. The parameters were: type of SPME fiber, exposure time and desorption time at the injection port of the GC. Headspace SPME procedure was carried out in samples with crystals of TNT buried in soil. These samples were analyzed under important environmental conditions such as temperature and water content. Analyses at contact times after the TNT-soil mix preparation were carried out during 1 month. A comparison of results from both techniques was performed. Vapors of TNT and 2,4-DNT were found predominantly in the samples. HS-SPME coupled with GC-μ ECD and TEEM GC/MS exhibited excellent selectivity and sensitivity.
Landmine detection is an important task for military operations and for humanitarian demining. Conventional methods for landmine detection involve measurements of physical properties. Several of these methods fail on the detection of modern mines with plastic enclosures. Methods based on the detection signature explosives chemicals such as TNT and DNT are specific to landmines and explosive devices. However, such methods involve the measurements of the vapor trace, which can be deceiving of the actual mine location because of the complex transport phenomena that occur in the soil neighboring the buried landmine. We report on the results of the study of the explosives subject to similar environmental conditions as the actual mines. Soil samples containing TNT were used to study the effects of aging, temperature and moisture under controlled conditions. The soil used in the investigation was Ottawa sand. A JEOL GCMate II gas chromatograph ñ mass spectrometer coupled to a Tunable Electron Energy Monochromator (TEEM-GC/MS) was used to develop the method of analysis of explosives under enhanced detection conditions. Simultaneously, a GC with micro cell 63Ni, Electron Capture Detector (μECD) was used for analysis of TNT in sand. Both techniques were coupled with Solid-Phase Micro Extraction (SPME) methodology to collect TNT doped sand samples. The experiments were done in both, headspace and immersion modes of SPME for sampling of explosives. In the headspace experiments it was possible to detect appreciable TNT vapors as early as 1 hour after of preparing the samples, even at room temperature (20 °C). In the immersion experiments, I-SPME technique allowed for the detection of concentrations as low as 0.010 mg of explosive per kilogram of soil.