3.3 Characteristics of IMS spectra of the collected explosive
vapor samples
Figure 4 shows the IMS spectra of TNT vapors (24 ng/L) collected in the
LCP. The TNT ion was detected for both the horizontal and vertical
arrangements. The TNT ion peak is [TNT –
H]-.7,28-30 For the horizontal
arrangement, the TNT ion peak was more intensively observed at 5 – 6
sec after the sample inlet. For the vertical arrangement, the TNT ion
peak was more intensively detected at 5 – 6 sec after the sample inlet
and it was observed until 10 sec. Detection sensitivity for the vertical
arrangement was better than that for the horizontal arrangement, which
was unexpected; however, it can be attributed to the flexibility and
adsorption ability of the thin LCP (0.03 mm thickness). The LCP arranged
with the horizontal position is fixed at the bottom and explosive vapor
is adsorbed on the upper side, whereas for the vertical arrangement it
is movable and explosive vapor is adsorbed on the both sides.
In the IMS spectra of TNT vapors (49 ng/L) adsorbed on the SSM, the TNT
ion was detected at 36.3 ms for the horizontal arrangement, but it was
not observed for the vertical arrangement (Figure S3; Supplementary
Information). The TNT ion peak was more intensively observed at 5 – 6
sec after the sample inlet. In the IMS spectra of RDX vapors (24 ng/L)
adsorbed on the PFS, the RDX ion was detected at approximately 38 ms for
both the horizontal and vertical arrangements, but its intensity was
weak (Figure S4; Supplementary Information). The intensity of the RDX
ion peak was greater at longer delay times, which may be attributed to
low volatility of RDX.
Figure 5 shows the IMS spectra of RDX vapors (49 ng/L) adsorbed on the
LCP. For the horizontal arrangement, the RDX ion was detected at the
delay time of 1 – 3 sec and two ion peaks were observed after 5 sec.
The two RDX-related ions correspond to [RDX + Cl]-and [RDX +
NO2]-.28-31 For
the vertical arrangement, the two RDX-related ions were clearly detected
at 37.3 and 39.5 ms after 5 sec. Similar to the TNT case, the detection
sensitivity for the vertical arrangement of the LCP was greater than
that for the horizontal arrangement, which is also because of the
flexibility and adsorption ability of the LCP as discussed above.