Compact GC-QEPAS for On-Site Analysis of Chemical Threats

Abstract

This paper reports on a compact, portable, and selective chemical sensor for hazardous vapors at trace levels, which is under development and validation within the EU project H2020 "RISEN". Starting from the prototype developed for a previous EU project, here, we implemented an updated two-stage purge and trap vapor pre-concentration system, a more compact MEMS- based fast gas-chromatographic separation module (Compact-GC), a new miniaturized quartz-enhanced photoacoustic spectroscopy (QEPAS) detector, and a new compact laser source. The system provides two-dimensional selectivity combining GC retention time and QEPAS spectral information and was specifically designed to be rugged, portable, suitable for on-site analysis of a crime scene, with accurate response in few minutes and in the presence of strong chemical background. The main upgrades of the sensor components and functional modules will be presented in detail, and test results with VOCs, simulants of hazardous chemical agents, and drug precursors will be reported and discussed.

Keywords: MEMS GC; QEPAS; forensic; gas analyzer; safety and security.

Figure 1

Sensing chain of the GC-QEPAS sensor upgraded for RISEN.

Figure 2

GC-QEPAS sensor assembled for RISEN.

Figure 3

Compact-GC prototype (a) and rendering of core components (b).

Figure 4

Miniaturized QEPAS cell.

Figure 5

Composite amplifier scheme.

Figure 6

Total absorption chromatogram (a) obtained for a sampled mix of acetone and DPGME; spectra measured (blue line) and corresponding best fit from database (red line) of acetone (b) and DPGME (d) at the corresponding peaks of integral absorbance. A third intermediate peak was observed, whose corresponding measured and best-fit database spectra (c) correspond to acetic acid.

Figure 7

Total absorption chromatograms obtained by desorbing in air at 280 °C (a) or at 180 °C (b) vapors of acetone by means of the first-stage pre-concentrator, showing how high temperature could promote partial conversion of acetone into acetic acid.

Figure 8

Color map (on the left) obtained by analyzing of a mix of saturated vapors of gasoline plus ~4 ppm of DMMP. The elution time is on the horizontal axis, the wavelength of acquired photoacoustic spectra is on the vertical axis, and the color bar is related to the intensity of the measured spectra. The spectrum acquired at 120 s, allowing one to identify the DMMP by comparison with the database, is plotted on the right.

Figure 9

Analysis of BMK. (a): color map obtained as described in Figure 8; (b): the corresponding total absorption chromatogram; (c–e): spectra acquired at ca. 80 s, 115 s, and 150 s, allowing one to identify acetic acid, benzaldehyde, and BMK, respectively.

Figure 10

Analysis of a mix of DMMP, DPGME, methyl salicylate, and safrole. (a): color map obtained as described in Figure 8; (b–e): spectra acquired at ca. 110 s, 120 s, 160 s, and 170 s, allowing one to identify DMMP, DPGME, safrole, and methyl salicylate, respectively.