Financial support was provided by the Department of Homeland Security Science and Technology Directorate.

1. Instrument Preparation
<ol>
	<li>Ensure the instrument, oven, and detector are at RT. Turn off gas flow to the inlet and detector.</li>
	<li>Remove the TDS from the GC. Consult the manufacturer&#8217;s user manual for the instrument-specific procedure.</li>
	<li>Remove the TDS adaptor from the CIS inlet and remove the liner from the CIS.</li>
	<li>Inspect the CIS inlet for particles and debris while the liner is removed. Clean any visible debris with compressed air, or preferably nitrogen.</li>
	<li>Attach a new gra...

<ol>
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Reproducibility is a critical attribute for the quantitation of trace explosive vapors using the direct liquid deposition method with TDS-CIS-GC-ECD instrumentation, and Relative Standard Deviation (RSD) is often used as a metric for reproducibility. We have experienced RSDs for inter- and intra-sample reproducibility of approximately 5% for TNT and 10% for RDX. Any RSD above 15% is used as an indicator to check common sources of variation that reduce the effectiveness of the protocol. Sources of variation that have led ...

Gas Chromatography (GC) is a core instrumental analysis technique of Analytical Chemistry and is arguably as ubiquitous as a hot plate or balance in a chemistry laboratory. GC instrumentation can be used for the preparation, identification, and quantitation of a multitude of chemical compounds and can be coupled to a variety of detectors, such as flame ionization detectors (FIDs), photo-ionization detectors (PIDs), thermal conductivity detectors (TCDs), electron capture detectors (ECDs), and mass spectrometers (MS), depending on the analytes, methodology, and application. Samples can be introduced through a standard split/splitless inlet when working with small sample solutions, specialized headspace analysis inlets, solid phase micro-extraction (SPME) syringes, or thermal desorption systems. GC-MS is often the standard technique used in validation and verification applications of alternative or emerging, detection techniques because of its utility, flexibility, and identification power with established chemical databases and libraries.1&#8211;7 GC and its related sampling and detecting components is ideal for routine chemical analysis and more specialized, challenging analytical applications.
An analytical application of increasing interest to military, homeland security, and commercial enterprises is trace explosive vapor detection, with detection including identification and quantitation. Trace explosive vapor detection is an unique analytical chemistry challenge because the analytes, such as 2,4,6-trinitrotoluene (TNT) and cyclotrimethylenetrinitramine (RDX) have physical properties that make them especially difficult to handle and separate using broader, more generic chemical analysis methodologies. The relatively low vapor pressures and sub parts-per-million by volume (ppmv) saturated vapor concentration, combined with relatively high sticking coefficients, necessitate special sampling protocols, instrumentation, and quantitation methods.8&#8211;12 A GC coupled to an Electron Capture Detector (ECD) or mass spectrometer (MS) is an effective method for quantitating explosive analytes, specifically dinitrotoluene (DNT), TNT, and RDX.6,13&#8211;17 GC-ECD is particularly useful for nitro-energetic compounds because of their relatively high electron affinity. The U.S. Environmental Protection Agency (EPA) has created standard methods for explosive analyte detection using GC-ECD and GC-MS, but these methods have focused on samples in solution, such as ground water, and not samples collected in the vapor phase.2,18&#8211;23 In order to detect explosive vapors, alternative sampling protocols must be used, such as vapor collection with sorbent-filled thermal desorption sample tubes, but quantitative detection remains difficult due to lack of vapor standards and calibration methods that do not account for sample tube and instrumentation losses.
Recently, quantitation methods using thermal desorption systems with a cooled inlet system (TDS-CIS), coupled to a GC-ECD have been developed for TNT and RDX vapors.24,25 The losses associated with the TDS-CIS-GC-ECD instrumentation for trace explosive vapors were characterized and accounted for in example calibration curves using a direct liquid deposition method onto sorbent-filled thermal desorption sample tubes. However, the literature focused on instrumentation characterization and method development but never actually sampled, analyzed, or quantitated explosive vapors, only solution standards. Herein, the focus is on the protocol for sampling and quantitating explosive vapors. The protocol and methodology can be expanded to other analytes and trace explosive vapors, such as Pentaerythritol tetranitrate (PETN).

<table border="0" cellpadding="0" cellspacing="0" width="638">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Name of Material/ Equipment</td>
			<td style="width:127px;">Company</td>
			<td style="width:128px;">Catalog Number</td>
			<td style="width:167px;">Comments/Description</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;width:216px;">2,4,6-Trinitrotoluene (TNT)</td>
			<td style="width:127px;">Accu-Standard</td>
			<td style="width:128px;">M-8330-11-A-10X</td>
			<td>10,000 ng &#956;L-1</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Cyclotrimethylenetrinitramine (RDX)</td>
			<td style="width:127px;">Accu-Standard</td>
			<td style="width:128px;">M-8330-05-A-10X</td>
			<td>10,000 ng &#956;L-1</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;width:216px;">3,4-Dinitrotoluene (3,4-DNT)</td>
			<td style="width:127px;">Accu-Standard</td>
			<td style="width:128px;">S-22988-01</td>
			<td>1000 ng &#956;L-1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tenax&#174; TA Vapor Sample Tubes</td>
			<td style="width:127px;">Gerstel</td>
			<td style="width:128px;">009947-000-00</td>
			<td>Tenax&#174; 60/80</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">CIS4 Liner</td>
			<td style="width:127px;">Gerstel</td>
			<td style="width:128px;">014652-005-00</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Transfer Line Ferrule</td>
			<td style="width:127px;">Gerstel</td>
			<td style="width:128px;">001805-008-00</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Inlet Liner Ferrule</td>
			<td style="width:127px;">Gerstel</td>
			<td style="width:128px;">001805-040-00</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">CIS4 Ferrule</td>
			<td style="width:127px;">Gerstel</td>
			<td style="width:128px;">007541-010-00</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">ECD Detector Ferrule</td>
			<td style="width:127px;">Aglient</td>
			<td style="width:128px;">5181-3323</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">DB5-MS Column</td>
			<td style="width:127px;">Res-Tek</td>
			<td style="width:128px;">12620</td>
			<td></td>
		</tr>
	</tbody>
</table>

quantitative detection of trace explosive vapors by programmed temperature desorption gas chromatography-electron capture detector

The direct liquid deposition of solution standards onto sorbent-filled thermal desorption tubes is used for the quantitative analysis of trace explosive vapor samples. The direct liquid deposition method yields a higher fidelity between the analysis of vapor samples and the analysis of solution standards than using separate injection methods for vapors and solutions, i.e., samples collected on vapor collection tubes and standards prepared in solution vials. Additionally, the method can account for instrumentation losses, which makes it ideal for minimizing variability and quantitative trace chemical detection. Gas chromatography with an electron capture detector is an instrumentation configuration sensitive to nitro-energetics, such as TNT and RDX, due to their relatively high electron affinity. However, vapor quantitation of these compounds is difficult without viable vapor standards. Thus, we eliminate the requirement for vapor standards by combining the sensitivity of the instrumentation with a direct liquid deposition protocol to analyze trace explosive vapor samples.

Obtaining quantitative results for trace explosive vapor samples begins with establishing a calibration curve for the TDS-CIS-GC-ECD instrumentation using the direct liquid deposition method of solution standards onto sample tubes to account for instrument losses and differences between solution standards and vapor samples. The TDS-CIS-GC-ECD instrumentation and method for TNT and RDX trace analysis has been previously described in detail elsewhere, but the instrument parameters are summarized in Table 1...

Watch this Scientific Journal Video about Quantitative Detection of Trace Explosive Vapors by Programmed Temperature Desorption Gas Chromatography-Electron Capture Detector at JoVE.com

Quantitative Detection of Trace Explosive Vapors by Programmed Temperature Desorption Gas Chromatography-Electron Capture Detector

Trace explosive vapors of TNT and RDX collected on sorbent-filled thermal desorption tubes were analyzed using a programmed temperature desorption system coupled to GC with an electron capture detector. The instrumental analysis is combined with direct liquid deposition method to reduce sample variability and account for instrumentation drift and losses.

The direct liquid deposition of solution standards onto sorbent-filled thermal desorption tubes is used for the quantitative analysis of trace explosive ...

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19.5K Views.  U.S. Naval Research Laboratory. Trace explosive vapors of TNT and RDX collected on sorbent-filled thermal desorption tubes were analyzed using a programmed temperature desorption system coupled to GC with an electron capture detector. The instrumental analysis is combined with direct liquid deposition method to reduce sample variability and account for instrumentation drift and losses.