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 graphite ferrule to a new CIS liner using the manufacturer provided tool and instructions for ferrule-to-liner binding.</li>
	<li>Insert the liner with the attached graphite ferrule into the CIS. Replace the TDS adaptor and re-mount the TDS.</li>
	<li>Remove a new column from its packaging and remove the silicone protection from the ends of the column.</li>
	<li>Insert a nut and ferrule onto each end of the column. Use an ECD detector nut and ferrule for one end of the column and a CIS ferrule for the opposite end of the column.</li>
	<li>Using a ceramic column cutting tool, remove approximately 10 cm from each end of the column. Ensure the nuts and ferrules remain on the column but away from the end of the column to avoid clogging and debris.</li>
	<li>Secure the column into the oven using the instrument manufacturer guidelines. Insert the column into the inlet. Connect the other end of the column to the detector port. The depth of insertion is specific to instrument, inlet, and detector manufacturer. See the user manual and specifications for the exact column insertion depth. 
	NOTE: A pre-bake may be required for the column before connecting the opposite end of the column to the detector ports. Consult the column and instrument manufacturer documentation to determine if a pre-bake is required.</li>
	<li>Gently hand-tighten nuts and ferrules onto their respective ports for the inlet and detector. Using a wrench, tighten with approximately a quarter turn of rotation the nuts and ferrules. Too much force or over-tightening will damage the ferrules causing leaks or the column to break and clog.</li>
	<li>Bake out the TDS, inlet, column, and detector. A typical bake out consists of setting the temperature for all zones to just below the maximum operating temperature (typically 300 &#176;C) while flowing carrier gas for at least 2 hr.</li>
	<li>Cool all zones and retighten all nuts and ferrules to ensure leak-free operation. Heating and cooling during the bake out will cause the nuts and ferrules to loosen, which can introduce leaks.</li>
	<li>Load, or reload, the instrument method using the software interface. Verify correct temperatures and flow rates have been achieved. Instrumentation is ready for analysis.</li>
</ol>
2. Preparation of Standards
<ol>
	<li>Remove 1,000 ng &#181;l-1 3,4-DNT, 10,000 ng &#181;l-1 TNT, and 10,000 ng &#181;l-1 RDX from the freezer or refrigerator and allow the three stock solutions to reach RT.</li>
	<li>Dispense 100 &#956;l of stock 1,000 ng &#181;l-1 3,4-DNT and add 900 &#181;l of acetonitrile into an amber sample vial.</li>
	<li>Dispense 100 &#956;l of the 100 ng &#181;l-1 3,4-DNT solution from Step 2.2 and add 900 &#181;l of acetonitrile into an amber sample vial.</li>
	<li>Dispense 150 &#181;l of the 10 ng &#181;l-1 3,4-DNT solution from Step 2.3 and 4,850 &#181;l of acetonitrile into an amber sample vial. This is the internal standard for direct liquid deposition.</li>
	<li>Dispense 100 &#956;l of stock 10,000 ng &#181;l-1 TNT solution, 100 &#956;l of stock 10,000 ng &#181;l-1 RDX solution, and 800 &#181;l of acetonitrile into an amber sample vial.</li>
	<li>Dispense 100 &#956;l of the 1,000 ng &#181;l-1 TNT and RDX solution in Step 2.5 and 900 &#181;l of acetonitrile into an amber sample vial.</li>
	<li>Dispense 100 &#956;l of the 100 ng &#181;l-1 TNT and RDX solution from Step 2.6 and 900 &#181;l of acetonitrile into an amber sample vial.</li>
	<li>Dispense 100 &#956;l of the 10 ng &#181;l-1 TNT and RDX solution from Step 2.7 and 900 &#181;l of acetonitrile into an amber sample vial. This creates the 1.0 TNT/1.0 RDX ng &#956;l-1 solution standard ready for direct liquid deposition onto sample tubes.</li>
	<li>Dispense 60 &#181;l of the 10 ng &#181;l-1 solution in Step 2.7 and 940 &#181;l of acetonitrile into an amber sample vial. This creates the 0.6 TNT/0.6 RDX ng &#956;l-1 solution standard ready for direct liquid deposition onto sample tubes.</li>
	<li>Dispense 40 &#181;l of the 10 ng &#181;l-1 solution in Step 2.7 and 960 &#181;l of acetonitrile into an amber sample vial. This creates the 0.4 TNT/0.4 RDX ng &#956;l-1 solution standard ready for direct liquid deposition onto sample tubes.</li>
	<li>Dispense 20 &#181;l of the 10 ng &#181;l-1 solution in Step 2.7 and 980 &#181;l of acetonitrile into an amber sample vial. This creates the 0.2 TNT/0.2 RDX ng &#956;l-1 solution standard ready for direct liquid deposition onto sample tubes.</li>
	<li>Dispense 100 &#181;l of the 1.0 ng &#181;l-1 solution in Step 2.8 and 900 &#181;l of acetonitrile into an amber sample vial. This creates the 0.1 TNT/0.1 RDX ng &#956;l-1 solution standard ready for direct liquid deposition onto sample tubes.</li>
</ol>
3. Sample Collection
<ol>
	<li>Connect one sorbent-filled thermal desorption sample tube to a sample pump or similar equipment using a small piece of flexible silicone tubing. A red arrow is provided on the sample tubes indicating the air flow direction for sample adsorption, and it should be pointing in the direction of the silicone tubing and sample pump.</li>
	<li>Attach a piston flow meter to the sample tube at the opposite end from the sample pump attached in Step 3.1. Adjust the flow rate on the sample pump, or similar equipment, such that the flow rate is approximately 100 ml min-1 through the sample tube according to the readings from the piston flow meter. The flow rate should be set to &#177;5.0 ml min-1 of the 100 ml min-1 desired set point.</li>
	<li>Disconnect the piston flow meter from the sample tube and temporarily shut off the sample pump but leave the sample tube connected to the pump. The sample pump will be reactivated to begin sample collection. The sample tube is ready for collection.</li>
	<li>Place the sample tube with the still connected sample pump in the explosives vapor stream. The vapor source could be the headspace above a solid sample, an open environment, or a variety of analyte vaporization systems.</li>
	<li>Set a timer based on the approximate sampling times listed in Table 2. The sampling times are listed as a general guideline based on the suspected concentration of material in the vapor phase. These sampling times, with a flow rate of 100 ml min-1, will generally yield a mass in the center of the calibration curve, which is ideal for quantitation.</li>
	<li>Activate the sample pump and start the timer. Wait until the timer has stopped and shut off the sample pump. Disconnect the sample tube from the pump and place it in the packaging provided with the sample tube. Cap the tube and store for analysis.</li>
	<li>Record the unique serial number stamped onto each sample tube, the sample time, and the flow rate for the sample tube in a laboratory notebook. These values will be important for quantitation.</li>
</ol>
4. Calibration Curve Generation
<ol>
	<li>Pipet 5.0 &#181;l of the solution standard directly on the glass frit of an unused, conditioned sample tube. Hold the sample tube and pipet upright with a gloved hand during deposition.</li>
	<li>Repeat Step 4.1 for each of the six calibration standards onto three different sample tubes.</li>
	<li>Deposit 5 &#181;l of the 0.3 ng &#956;l-1 3,4-DNT on each of the tubes as well.</li>
	<li>Allow the eighteen sample tubes (three per solution concentration, six solution concentrations) to sit at RT for at least 30 min to evaporate the solvent.</li>
	<li>Use the twenty tube autosampler and the previously described TNT and RDX TDS-CIS-GC-ECD method to run and analyze all eighteen tubes O/N.24,25 A summary of the TDS-CIS-GC-ECD parameters for the method is provided in Table 1.</li>
	<li>Integrate the peaks associated with 3,4-DNT, TNT, and RDX in the chromatogram for each of the eighteen sample tubes. The 3,4-DNT, TNT and RDX peaks will occur at approximately 4.16, 4.49 and 4.95 min, respectively.</li>
	<li>Note the 3,4-DNT, TNT and RDX peak areas for each of the eighteen tubes along with the corresponding mass of TNT and RDX that was deposited on the sample tube in a spreadsheet and laboratory notebook.</li>
	<li>Normalize the peak areas for both TNT and RDX by dividing each peak area by the peak area for 3,4-DNT. Do this for all eighteen tubes.</li>
	<li>Calculate the average and standard deviation of the normalized TNT and RDX peak areas for the six standard concentrations.</li>
	<li>Plot the average normalized peak area versus mass of analyte present on the tubes for both TNT and RDX.</li>
	<li>Add a linear trend line for both the TNT and RDX data points. Identify the slope and y-intercept for each analyte. Record the slope, intercept, and R2 value in a spreadsheet and laboratory notebook.</li>
	<li>Place used sample tubes in a tube conditioner for 3 hr at 300 &#186;C and 500 ml min-1 nitrogen flow.</li>
</ol>
5. Sample Analysis
<ol>
	<li>Deposit 5.0 &#181;l of the 0.3 ng &#181;l-1 3,4-DNT on each of the sample tubes.</li>
	<li>Allow the tubes to sit at RT for at least 30 min to evaporate the solvent from the internal standard.</li>
	<li>Use the twenty tube autosampler and the previously described TNT and RDX method to run the tubes O/N on the TDS-CIS-GC-ECD.24,25 A summary of the instrumentation parameters for the analysis method is provided in Table 1.</li>
	<li>Integrate the peaks associated with 3,4-DNT, TNT, and RDX in the chromatogram for each of the eighteen sample tubes. The 3,4-DNT, TNT and RDX peaks will occur at approximately 4.16, 4.49 and 4.95 min, respectively.</li>
	<li>Note the 3,4-DNT, TNT and RDX peak areas for each of the sample tubes in a spreadsheet and laboratory notebook.</li>
	<li>Use the peak areas and calibration curve to calculate the vapor concentration in parts-per-billion by volume (ppbv) for each analyte. See Equations 1-4.</li>
	<li>Place used sample tubes in a tube conditioner for 3 hr at 300 &#186;C and 500 ml min-1 nitrogen air flow.</li>
</ol>

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We have nothing to disclose.

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).

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			<td height="42" style="height:42px;width:216px;">Name of Material/ Equipment</td>
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		</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 ...

quantitative-detection-trace-explosive-vapors-programmed-temperature

Research

JoVE Journal

Chemistry

19.6K vistas.  U.S. Naval Research Laboratory.  Traza vapores explosivos de TNT y RDX recogidos en tubos de desorción térmica de sorbente lleno se analizaron mediante un sistema de desorción a temperatura programada acoplada a GC con un detector de captura de electrones. El análisis instrumental se combina con el método de deposición directa de líquido para reducir la variabilidad de la muestra y de la cuenta de la deriva y las pérdidas de la instrumentación. 

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

Determination of the Gas-phase Acidities of Oligopeptides

Amino acid residues located at different positions in folded proteins often exhibit different degrees of acidities. For example, a cysteine residue located at or near the N-terminus of a helix is often more acidic than that at or near the C-terminus 1-6. Although extensive experimental studies on the acid-base properties of peptides have been carried out in the condensed phase, in particular in aqueous solutions 6-8, the results are often complicated by solvent effects 7. In fact, most of the active sites in proteins are located near the interior region where solvent effects have been minimized 9,10. In order to understand intrinsic acid-base properties of peptides and proteins, it is important to perform the studies in a solvent-free environment.
We present a method to measure the acidities of oligopeptides in the gas-phase. We use a cysteine-containing oligopeptide, Ala3CysNH2 (A3CH), as the model compound. The measurements are based on the well-established extended Cooks kinetic method (Figure 1) 11-16. The experiments are carried out using a triple-quadrupole mass spectrometer interfaced with an electrospray ionization (ESI) ion source (Figure 2). For each peptide sample, several reference acids are selected. The reference acids are structurally similar organic compounds with known gas-phase acidities. A solution of the mixture of the peptide and a reference acid is introduced into the mass spectrometer, and a gas-phase proton-bound anionic cluster of peptide-reference acid is formed. The proton-bound cluster is mass isolated and subsequently fragmented via collision-induced dissociation (CID) experiments. The resulting fragment ion abundances are analyzed using a relationship between the acidities and the cluster ion dissociation kinetics. The gas-phase acidity of the peptide is then obtained by linear regression of the thermo-kinetic plots 17,18.
The method can be applied to a variety of molecular systems, including organic compounds, amino acids and their derivatives, oligonucleotides, and oligopeptides. By comparing the gas-phase acidities measured experimentally with those values calculated for different conformers, conformational effects on the acidities can be evaluated.

The determination of the gas-phase acidities of cysteine-containing oligopeptides is described. The experiments are performed using a triple quadrupole mass spectrometer. The relative acidities of the peptides are measured using collision-induced dissociation experiments, and the quantitative acidities are determined using the extended Cooks kinetic method.

Amino acid residues located at different positions in folded proteins often exhibit different degrees of acidities. For example, a cysteine residue ...

Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow

While the first Electron Paramagnetic Resonance (EPR) studies regarding the effects of oxidation on the structure and stability of carbon radicals date back to the early 1980s the focus of these early papers primarily characterized the changes to the structures under extremely harsh conditions (pH or temperature)1-3. It is also known that paramagnetic molecular oxygen undergoes a Heisenberg spin exchange interaction with stable radicals that extremely broadens the EPR signal4-6. Recently, we reported interesting results where this interaction of molecular oxygen with a certain part of the existing stable radical structure can be reversibly affected simply by flowing a diamagnetic gas through the carbon samples at STP7. As flows of He, CO2, and N2 had a similar effect these interactions occur at the surface area of the macropore system.
This manuscript highlights the experimental techniques, work-up, and analysis towards affecting the existing stable radical nature in the carbon structures. It is hoped that it will help towards further development and understanding of these interactions in the community at large.

Stable radicals that are present in carbon substrates interact with paramagnetic oxygen through a Heisenberg spin exchange. This interaction can be significantly reduced under STP conditions by flowing a diamagnetic gas over the carbon system. This manuscript describes a simple method to characterize the nature of those radicals.

While the first Electron Paramagnetic Resonance (EPR) studies regarding the effects of oxidation on the structure and stability of carbon radicals date ...

Facile Preparation of 4-Substituted Quinazoline Derivatives

Reported in this paper is a very simple method for direct preparation of 4-substituted quinazoline derivatives from a reaction between substituted 2-aminobenzophenones and thiourea in the presence of dimethyl sulfoxide (DMSO). This is a unique complementary reaction system in which thiourea undergoes thermal decomposition to form carbodiimide and hydrogen sulfide, where the former reacts with 2-aminobenzophenone to form 4-phenylquinazolin-2(1H)-imine intermediate, whilst hydrogen sulfide reacts with DMSO to give methanethiol or other sulfur-containing molecule which then functions as a complementary reducing agent to reduce 4-phenylquinazolin-2(1H)-imine intermediate into 4-phenyl-1,2-dihydroquinazolin-2-amine. Subsequently, the elimination of ammonia from 4-phenyl-1,2-dihydroquinazolin-2-amine affords substituted quinazoline derivative. This reaction usually gives quinazoline derivative as a single product arising from 2-aminobenzophenone as monitored by GC/MS analysis, along with small amount of sulfur-containing molecules such as dimethyl disulfide, dimethyl trisulfide, etc. The reaction usually completes in 4-6 hr at 160 &#186;C in small scale but may last over 24 hr when carried out in large scale. The reaction product can be easily purified by means of washing off DMSO with water followed by column chromatography or thin layer chromatography.

A protocol for facile preparation of 4-substituted quinazoline derivatives from 2-aminobenzophenones, thiourea and dimethyl sulfoxide is presented.

Reported in this paper is a very simple method for direct preparation of 4-substituted quinazoline derivatives from a reaction between substituted ...

Temperature-programmed Deoxygenation of Acetic Acid on Molybdenum Carbide Catalysts

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system includes a reactor, furnace, gas and vapor sources, flow control, instrumentation to quantify reaction products (e.g., gas chromatograph), and instrumentation to monitor the reaction in real time (e.g., mass spectrometer). Here, we apply the TPRxn methodology to study molybdenum carbide catalysts for the deoxygenation of acetic acid, an important reaction among many in the upgrading/stabilization of biomass pyrolysis vapors. TPRxn is used to evaluate catalyst activity and selectivity and to test hypothetical reaction pathways (e.g., decarbonylation, ketonization, and hydrogenation). The results of the TPRxn study of acetic acid deoxygenation show that molybdenum carbide is an active catalyst for this reaction at temperatures above ca. 300 &#176;C and that the reaction favors deoxygenation (i.e., C-O bond-breaking) products at temperatures below ca. 400 &#176;C and decarbonylation (i.e., C-C bond-breaking) products at temperatures above ca. 400 &#176;C.

Presented here is a protocol for the operation of a micro-scale temperature-programmed reactor for evaluating the catalytic performance of molybdenum carbide during acetic acid deoxygenation.

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system ...

Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This flexible tool offers a detailed observation of chemical gas-phase kinetics in reacting flows under well-controlled conditions. The vast range of operating conditions available in a laminar flow reactor enables access to extraordinary combustion applications that are typically not achievable by flame experiments. These include rich conditions at high temperatures relevant for gasification processes, the peroxy chemistry governing the low temperature oxidation regime or investigations of complex technical fuels. The presented setup allows measurements of quantitative speciation data for reaction model validation of combustion, gasification and pyrolysis processes, while enabling a systematic general understanding of the reaction chemistry. Validation of kinetic reaction models is generally performed by investigating combustion processes of pure compounds. The flow reactor has been enhanced to be suitable for technical fuels (e.g. multi-component mixtures like Jet A-1) to allow for phenomenological analysis of occurring combustion intermediates like soot precursors or pollutants. The controlled and comparable boundary conditions provided by the experimental design allow for predictions of pollutant formation tendencies. Cold reactants are fed premixed into the reactor that are highly diluted (in around 99 vol% in Ar) in order to suppress self-sustaining combustion reactions. The laminar flowing reactant mixture passes through a known temperature field, while the gas composition is determined at the reactors exhaust as a function of the oven temperature. The flow reactor is operated at atmospheric pressures with temperatures up to 1,800 K. The measurements themselves are performed by decreasing the temperature monotonically at a rate of -200 K/h. With the sensitive MBMS technique, detailed speciation data is acquired and quantified for almost all chemical species in the reactive process, including radical species.

An investigation of the oxidative combustion chemistry of novel biofuels, fuel components, or jet fuels by comparison of quantitative speciation data is presented. The data can be used for kinetic model validation and enables fuel assessment strategies.This manuscript describes the atmospheric high-temperature flow reactor and demonstrates its capabilities.

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This ...

Reducing Willow Wood Fuel Emission by Low Temperature Microwave Assisted Hydrothermal Carbonization

Biomass is a sustainable fuel, as its CO2 emissions are reintegrated in biomass growth. However, the inorganic precursors in the biomass cause a negative environmental impact and slag formation. The selected short rotation coppice (SRC) willow wood has a high ash content (<img alt="Equation 1" src="/files/ftp_upload/58970/58970eq1.jpg" /> = 1.96%) and, therefore, a high content of emission and slag precursors. Therefore, the reduction of minerals from SRC willow wood by low temperature microwave assisted hydrothermal carbonization (MAHC) at 150 &#176;C, 170 &#176;C, and 185 &#176;C is investigated. An advantage of MAHC over conventional reactors is an even temperature conductance in the reaction medium, as microwaves penetrate the whole reactor volume. This allows a better temperature control and a faster cooldown. Therefore, a succession of depolymerization, transformation and repolymerization reactions can be analyzed effectively. In this study, the analysis of the mass loss, ash content and composition, heating values and molar O/C and H/C ratios of the treated and untreated SCR willow wood showed that the mineral content of the MAHC coal was reduced and the heating value increased. The process water showed a decreasing pH and contained furfural and 5-methylfurfural. A process temperature of 170 &#176;C showed the best combination of energy input and ash component reduction. The MAHC allows a better understanding of the hydrothermal carbonization process, while a large-scale industrial application is unlikely because of the high investment costs.

A protocol for the emission precursor depletion from low quality biomass by low temperature microwave assisted hydrothermal carbonization treatment is presented. This protocol includes the microwave parameters and the analysis of the biocoal product and process water.

Biomass is a sustainable fuel, as its CO2 emissions are reintegrated in biomass growth. However, the inorganic precursors in the biomass cause a negative ...

A Two-Step Pyrolysis-Gas Chromatography Method with Mass Spectrometric Detection for Identification of Tattoo Ink Ingredients and Counterfeit Products

Tattoo inks are complex mixtures of ingredients. Each of them possesses different chemical properties which have to be addressed upon chemical analysis. In this method for two-step pyrolysis online coupled to gas chromatography mass spectrometry (py-GC-MS) volatile compounds are analyzed during a first desorption run. In the second run, the same dried sample is pyrolyzed for analysis of non-volatile compounds such as pigments and polymers. These can be identified by their specific decomposition patterns. Additionally, this method can be used to differentiate original from counterfeit inks. Easy screening methods for data evaluation using the average mass spectra and self-made pyrolysis libraries are applied to speed up substance identification. Using specialized evaluation software for pyrolysis GS-MS data, a fast and reliable comparison of the full chromatogram can be achieved. Since GC-MS is used as separation technique, the method is limited to volatile substances upon desorption and after pyrolysis of the sample. The method can be applied for quick substance screening in market control surveys since it requires no sample preparation steps.

This method for two-step pyrolysis online coupled to gas chromatography with mass spectrometric detection and data evaluation protocol can be used for multi-component analysis of tattoo inks and discrimination of counterfeit products.

Tattoo inks are complex mixtures of ingredients. Each of them possesses different chemical properties which have to be addressed upon chemical analysis. ...

Analysis of Complex Molecules and Their Reactions on Surfaces by Means of Cluster-Induced Desorption/Ionization Mass Spectrometry

Desorption/Ionization Induced by Neutral SO2 Clusters (DINeC) is employed as a very soft and efficient desorption/ionization technique for mass spectrometry (MS) of complex molecules and their reactions on surfaces. DINeC is based on a beam of SO2 clusters impacting on the sample surface at low cluster energy. During cluster-surface impact, some of the surface molecules are desorbed and ionized via dissolvation in the impacting cluster; as a result of this dissolvation-mediated desorption mechanism, low cluster energy is sufficient and the desorption process is extremely soft. Both surface adsorbates and molecules of which the surface is composed of can be analyzed. Clear and fragmentation-free spectra from complex molecules such as peptides and proteins are obtained. DINeC does not require any special sample preparation, in particular no matrix has to be applied. The method yields quantitative information on the composition of the samples; molecules at a surface coverage as low as 0.1 % of a monolayer can be detected. Surface reactions such as H/D exchange or thermal decomposition can be observed in real-time and the kinetics of the reactions can be deduced. Using a pulsed nozzle for cluster beam generation, DINeC can be efficiently combined with ion trap mass spectrometry. The matrix-free and soft nature of the DINeC process in combination with the MSn capabilities of the ion trap allows for very detailed and unambiguous analysis of the chemical composition of complex organic samples and organic adsorbates on surfaces.

Neutral SO2 clusters of low kinetic energy (&#60; 0.8 eV/constituent) are used to desorb complex surface molecules such as peptides or lipids for further analysis by means of mass spectrometry using an ion trap mass spectrometer. No special sample preparation is required, and real-time observation of reactions is possible.

Desorption/Ionization Induced by Neutral SO2 Clusters (DINeC) is employed as a very soft and efficient desorption/ionization technique for mass ...

Nitrogen Compound Characterization in Fuels by Multidimensional Gas Chromatography

Certain nitrogen-containing compounds can contribute to fuel instability during storage. Hence, detection and characterization of these compounds is crucial. There are significant challenges to overcome when measuring trace compounds in a complex matrix such as fuels. Background interferences and matrix effects can create limitations to routine analytical instrumentation, such as GC-MS. In order to facilitate specific and quantitative measurements of trace nitrogen compounds in fuels, a nitrogen-specific detector is ideal. In this method, a nitrogen chemiluminescence detector (NCD) is used to detect nitrogen compounds in fuels. NCD utilizes a nitrogen-specific reaction that does not involve the hydrocarbon background. Two-dimensional (GCxGC) gas chromatography is a powerful characterization technique as it provides superior separation capabilities to one-dimensional gas chromatography methods. When GCxGC is paired with a NCD, the problematic nitrogen compounds found in fuels can be extensively characterized without background interference. The method presented in this manuscript details the process for measuring different nitrogen-containing compound classes in fuels with little sample preparation. Overall, this GCxGC-NCD method has been shown to be a valuable tool to enhance the understanding of the chemical composition of nitrogen-containing compounds in fuels and their impact on fuel stability. The % RSD for this method is &#60;5% for intraday and &#60;10% for interday analyses; the LOD is 1.7 ppm and the LOQ is 5.5 ppm.

Here, we present a method utilizing two-dimensional gas chromatography and nitrogen chemiluminescence detection (GCxGC-NCD) to extensively characterize the different classes of nitrogen-containing compounds in diesel and jet fuels.

Certain nitrogen-containing compounds can contribute to fuel instability during storage. Hence, detection and characterization of these compounds is ...

Chromatographic Fingerprinting by Template Matching for Data Collected by Comprehensive Two-Dimensional Gas Chromatography

Data processing and evaluation are critical steps of comprehensive two-dimensional gas chromatography (GCxGC), particularly when coupled to mass spectrometry. The rich information encrypted in the data may be highly valuable but difficult to access efficiently. Data density and complexity can lead to long elaboration times and require laborious, analyst-dependent procedures. Effective yet accessible data processing tools, therefore, are key to enabling the spread and acceptance of this advanced multidimensional technique in laboratories for daily use. The data analysis protocol presented in this work uses chromatographic fingerprinting and template matching to achieve the goal of highly automated deconstruction of complex two-dimensional chromatograms into individual chemical features for advanced recognition of informative patterns within individual chromatograms and across sets of chromatograms. The protocol delivers high consistency and reliability with little intervention. At the same time, analyst supervision is possible in a variety of settings and constraint functions that can be customized to provide flexibility and capacity to adapt to different needs and goals. Template matching is shown here to be a powerful approach to explore extra-virgin olive oil volatilome. Cross-alignment of peaks is performed not only for known targets, but also for untargeted compounds, which significantly increases the characterization power for a wide range of applications. Examples are presented to evidence the performance for the classification and comparison of chromatographic patterns from sample sets analyzed under similar conditions.

This protocol presents an approach to fingerprint and explore multi-dimensional data collected by comprehensive two-dimensional gas chromatography coupled to mass spectrometry. Dedicated pattern recognition algorithms (template matching) are applied to explore the chemical information encrypted in the extra-virgin olive oil volatile fraction (i.e., volatilome).