Abstract
The detection of trace amounts of explosives in the vapor phase is of great importance. Preconcentration of the analyte is a useful technique to lower the detection limit of existing sensors. A nanoporous silica (pSiO2) substrate was evaluated as a preconcentrator for gas-phase 2,3-dimethyl-2,3-dinitrobutane (DMNB), a volatile detection taggant added by law to plastic explosives. After collection in pSiO2, the DMNB vapor was thermally desorbed at 70 °C into a gas chromatography–mass spectrometry sorbent tube. This was analyzed for the total mass of DMNB collected in pSiO2. The loading time and loading temperature of pSiO2 were varied systematically between 15 and 60 min and 5–20 °C, respectively. The preconcentrator’s performance was compared to that of a nonporous substrate of the same material as a control. The collection efficiency of pSiO2 was calculated as approximately 20% of the total DMNB that passed over it in 30 min, at a concentration of 0.5 ppm in N2 carrier gas. It had enhancement factors compared to the nonporous substrate of 12 and 16 for 0.5 and 4.1 ppm DMNB, respectively, under the same conditions. No advantage was found with cooling pSiO2 below room temperature during the loading phase, which removes any need for a cooling system to aid preconcentration. The low desorption temperature of 70 °C is an advantage over other preconcentration systems, although a higher temperature could decrease the desorption time.
Highlights
With the rise of global terrorism, as well as of other security and military applications, the reliable detection of explosives has risen greatly in importance over the last several decades
The temperature of the silica substrate was set via the Peltier device; DMNB in N2 at a fixed concentration was passed through the cell for a defined amount of time
This work has shown that the pSiO2 preconcentrator provides a substantial advantage over a flat surface in its ability to collect DMNB
Summary
With the rise of global terrorism, as well as of other security and military applications, the reliable detection of explosives has risen greatly in importance over the last several decades. Has been used for a similar purpose: Camara et al have published several papers on carbon (in the form of powder, nanotubes, or graphitized carbon) deposited inside porous silicon microchannels This material is used as a preconcentrator for gaseous benzene and nonexplosive aromatic nitro compounds, such as nitrobenzene and dinitrotoluene (DNT).[12−14] A preconcentration factor (the ratio between the maximum measured concentration during desorption and the injected concentration) of about 60 was achieved for benzene; the preconcentration factors for other compounds were not reported.[14] High desorption temperatures between 200 and 300 °C were required throughout. A nonporous piece of surface-oxidized silicon was used as a control
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