3.1 Explosive vapor collection efficiency depending on the
collection matrix
The experimental results are summarized in Table 1. Among the 15
collection matrices, only three matrices of the SSM, PFS, and LCP showed
the TNT and/or RDX ion peaks in the IMS spectra at the explosive vapor
concentration lower than 49 ng/L. There was no collection matrix to
detect PETN at a vapor concentration lower than 49 ng/L. For the SSM,
only TNT at 49 ng/L vapor concentration was detected for the horizontal
position. For the PFS, TNT and RDX were detected at 49 ng/L vapor
concentration irrespective of the arrangement types. For the LCP, TNT
was detected at 24 ng/L vapor concentration and RDX was observed at 49
ng/L vapor concentration irrespective of the arrangements.
The base side area of the hood was 90 × 64 = 5760 cm2,
and the size of the collection matrix was 5 × 8 = 40
cm2. Thus, for the horizontal position, each
collection matrix covered 0.7% of the hood base. If 20 µg artificial
vapor completely and evenly spreads down to the hood base without any
loss, the maximum amount adsorbed on each collection matrix will be 140
ng. However, considerable amount of explosive vapor cannot reach the
hood base, because some explosive vapor will be adsorbed on the hood
wall during the spraying of solution and spreading of vapor. Considering
the adsorption of explosive vapor on the hood wall, a reasonable amount
of explosive vapor adsorbed on each collection matrix should be much
less than 140 ng. When 10 µg vapor is introduced into the hood, the
amount of explosive vapor adsorbed on each collection matrix should be
much less than 70 ng. Considering this situation, the corrected
detection limits of explosive vapors deposited on the collection
matrices are summarized in Table 2.