## 2 Experimental Section
### Materials and Methods  
A planar solid phase microextraction (PSPME) device is an acid-cured glass fiber filter (Fisher Scientific, Pittsburgh, PA, USA) that is spin-coated (Laurell Technologies Co., North Wales, PA, USA) with a sol-gel solution as previously described [2]. The size of the PSPME disk was modified in order to fit the geometry of the MobileTrace thermal desorption system. The PSPME for the bench-top instrument was introduced with the assistance of a Teflon holder (Field Forensics, St. Petersburg, FL, USA) without further modification. The different containers of varying materials and volumes sizes were used in this study. This includes metal quart and gallon cans (All-American Containers, Miami, FL, USA) of 0.94 and 3.8 L, respectively, as well as polypropylene plastic containers of 45 L (15.625 \(\times\) 13.125 \(\times\) 13.25 inches in dimension). Prior to use, the metal cans were baked at 100 \(\,\)C for over 24 h in order to remove residual volatiles from the manufacturing process and any background volatiles adsorbed on the surfaces of the cans. The plastic containers were used without further modification but blank samples revealed no interfering compounds. 10-500 mg of smokeless powders (Alliant Powder Unique (AU), Radford, VA, USA), IMR Powder Co. 4198 (Shawnee Mission, KS, USA) were placed directly in the containers or in a Petri-dish (Fisher Scientific) within the containers and sealed. All headspace studies were performed at room ambient temperature (\(\sim\)23 \(\,\)C). For equilibrium studies, static headspace sampling of 10 min was performed at different times after sealing the containers (0-72 h) and sampled in triplicate. The observed signals were plotted against the elapsed times to determine the headspace equilibrium within a given volume. Headspace PSPME extractions were performed statically, in which the PSPME disk was exposed to the headspace of the closed system for a given amount of time, as well as \begin{table}
\begin{tabular}{|c|c|c|c|c|c|c|c|} \hline \multirow{3}{*}{**Alarm**} & \multicolumn{4}{c|}{**Smits Detection IONSCAN**} & \multicolumn{4}{c|}{**Morpho Detection Hardened**} \\  & \multicolumn{4}{c|}{**MobileTrace**} \\ \cline{2-9}  & **Reduced mobility (K\({}_{\text{0}}\))** & **Variability (\(\mu\)s)** & **Amplitude threshold (d.u.)** & **Full width half max (\(\mu\)s)** & **Drift time (ms)** & **Variability (ms)** & **Method of detection** \\ \hline (+) DPA & 1.6082 & 50 & 30 & 327 & 6.080 & 0.040 & Height (100) \\ \hline (–) 2,4-DNT & 1.5660 & 50 & 30 & 253 & 5.548 & 0.040 & Height (300) \\ \hline (–) NG-N & 1.2720 & 45 & 25 & 335 & 3.833 & 0.035 & Height (700) \\ (–) NG-C & 1.3385 & 45 & 50 & 305 & 3.833 & 0.035 & Height (700) \\ \hline (–) ETn & & & & & 4.672 & 0.040 & Height (100) \\ \hline (–) PETn & & & & & 7.991 & 0.040 & Height (500) \\ \hline (–) RDX & & & & & 6.333 & 0.040 & Slope (1000) \\ \hline (–) TNT & & & & & 6.076 & 0.040 & Height (300) \\ \hline \end{tabular}
\end{table} 
Table 2: Alarm threshold for analytes of interest for benchtop and portable IMS systems. Military explosives were only detected using the portable IMS, thus, parameters for these analytes are only shown for the portable IMS. dynamically with the assistance of air flow using the Barringer remote DC sampler at 0.17 L s\({}^{-1}\) for no more than 1 min. Dynamic extractions were performed by lifting the lid of the containers and sampling with the lid on top of the sampling device in order to contain the vapors. Thirty replicates were performed for the TPR studies for each different defined scenario. ROC curves were constructed using a commercially available statistical analysis software (JMP v. 10). For SPME-GC-MS analysis, polydimethylsiloxane (PDMS) and PDMS/divinylbenzene (DVB) SPME fibers (Supelco, Sigma-Aldrich Corp., St. Louis, MO, USA) were both used for the sampling and headspace preconcentration and resulted in very similar extraction efficiency for the target volatile compounds.