Funding support for this work was provided by the Defense Logistics Agency Energy (DLA Energy) and the Naval Air Systems Command (NAVAIR).
This research was performed while an author held an NRC Research Associateship award at the U.S. Naval Research Laboratory.

CAUTION: Please consult relevant safety data sheets (SDS) of all compounds before use. Appropriate safety practices are recommended. All work should be performed while wearing personal protective equipment such as gloves, safety glasses, lab coat, long pants, and closed-toed shoes. All standard and sample preparations should be done in a ventilated hood.
1. Preparation of standards
<ol>
	<li>Prepare a 5,000 mg/kg (ppm) solution of carbazole (calibration standard, minimum of 98% purity) by placing 0.050 g in a vial and bring the total mass of each solution to 10.000 g with isopropyl alcohol. Cap the vial immediately to prevent loss of isopropyl alcohol. This is the calibration stock solution.</li>
	<li>Prepare a carbazole solution with 100 ppm nitrogen content by diluting 1.194 mL of stock solution to 5 mL with isopropyl alcohol. This is designated as &#34;100 ppm nitrogen carbazole&#34; and is used to create the calibration standards. 
	NOTE: The concentrations of the calibration standards indicate the concentration of nitrogen in the standard, not the carbazole concentration</li>
	<li>Prepare the following calibration standards by serial dilution: 
	20 ppm nitrogen carbazole 
	10 ppm nitrogen carbazole 
	5 ppm nitrogen carbazole 
	1 ppm nitrogen carbazole 
	0.5 ppm nitrogen carbazole 
	0.025 ppm nitrogen carbazole</li>
	<li>Put 1 mL of the calibration standards into separate GC vials (6 vials total).</li>
	<li>Prepare individual 10 ppm solutions of each standard compounds listed in Table 1 in isopropyl alcohol. Place 1 mL of each standard solution in separate GC vials (10 vials total). 
	NOTE: The standard compounds listed in Table 1 will be used to classify the unknown nitrogen compounds as &#39;light nitrogen compounds&#39;, &#39;basic nitrogen compounds&#39;, or &#39;non-basic nitrogen compounds&#39;.</li>
</ol>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Standard Compound</td>
			<td>Elution Time Classification Group</td>
		</tr>
		<tr>
			<td>Pyridine</td>
			<td>Group 1 &#8211; light nitrogen compounds</td>
		</tr>
		<tr>
			<td>Trimethylamine</td>
			<td>Group 1 &#8211; light nitrogen compounds</td>
		</tr>
		<tr>
			<td>Methylaniline</td>
			<td>Group 1 &#8211; light nitrogen compounds</td>
		</tr>
		<tr>
			<td>Quinoline</td>
			<td>Group 2 &#8211; basic nitrogen compounds</td>
		</tr>
		<tr>
			<td>Diethylaniline</td>
			<td>Group 2 &#8211; basic nitrogen compounds</td>
		</tr>
		<tr>
			<td>Methylquinoline</td>
			<td>Group 2 &#8211; basic nitrogen compounds</td>
		</tr>
		<tr>
			<td>Indole</td>
			<td>Group 2 &#8211; basic nitrogen compounds</td>
		</tr>
		<tr>
			<td>Dimethylindole</td>
			<td>Group 2 &#8211; basic nitrogen compounds</td>
		</tr>
		<tr>
			<td>Ethylcarbazole</td>
			<td>Group 3 &#8211; Non-basic nitrogen compounds</td>
		</tr>
		<tr>
			<td>Carbazole</td>
			<td>Group 3 &#8211; Non-basic nitrogen compounds</td>
		</tr>
	</tbody>
</table>
Table 1: Nitrogen standards and their elution classification groups.
2. Sample preparation
<ol>
	<li>For diesel fuels: In a GC vial, add 250 &#181;L of fuel sample and 750 &#181;L of isopropyl alcohol.</li>
	<li>For jet fuels: In a GC vial, add 750 &#181;L of fuel sample and 250 &#181;L of isopropyl alcohol. 
	NOTE: If the total nitrogen concentration of either diesel or jet fuel falls below the calibration curve (0.025 ppm nitrogen) when diluted as instructed above, do not dilute. If the nitrogen concentration in a specific nitrogen group in either diesel or jet fuel falls above the calibration curve (20 ppm nitrogen), dilute sample further.</li>
</ol>
3. Instrument setup
<ol>
	<li>Instrument configuration
	<ol>
		<li>Auto-sampler: Ensure that the autosampler tray and tower are installed with a splitless inlet and wash vials in place.</li>
		<li>Nitrogen Chemiluminescence Detector: Ensure that the nitrogen chemiluminescence detector is installed with the appropriate gas lines (i.e., helium and hydrogen). A hydrogen generator can be utilized instead of a tank, if available.</li>
		<li>Duel Loop Thermal Modulator: Ensure that the duel loop thermal modulator is installed and aligned properly so that the column loop will be centered between the cold and hot jet flows during modulation.</li>
	</ol>
	</li>
	<li>Column installation
	<ol>
		<li>Ensure that the instrument is in maintenance mode (i.e., all burners and gas flows are turned off).</li>
		<li>Insert the 30 m primary column into the GC oven and connect to the splitless inlet.</li>
		<li>Measure and cut 2.75 m of the secondary column. Put a mark on the secondary column at 0.375 m and 1.375 m using a white-out pen.</li>
		<li>Place the secondary column into the Zoex modulator column holder and use the marks as guides for creating a 1 m loop within the holder for modulation.</li>
		<li>Connect the shorter end of the secondary column to the primary column using a micro-union. Check for a successful connection by turning on the gas flow and inserting the open end of the column into a vial of methanol. A successful connection is confirmed by the presence of bubbles.</li>
		<li>Place the column holder into the modulator and adjust the loops as necessary so that the loops line up properly with the cold and hot jets, as pictured in Figure 1.</li>
		<li>Insert the other end of the column into the NCD burner. Then turn on all burners and gas flows to ensure there are no leaks.</li>
		<li>Turn the oven on at the maximum temperature limit for a minimum of 2 h in order to bake-out the columns. Once completed, verify that there are no new leaks. Then, cool the oven.</li>
	</ol>
	</li>
</ol>
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/60883/60883fig1.jpg" /> 
Figure 1: Schematic representation of the GCxGC-NCD instrumentation. This figure has been reprinted from Deese et al. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/60883/60883fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol start="3">
	<li>Method parameters
	<ol>
		<li>Using the computer software, set the instrument to the parameters listed in Table 2.</li>
		<li>Set the initial oven temperature to 60 &#176;C with a ramp rate of 5 &#176;C/min to 160 &#176;C, and then change the ramp rate to 4 &#176;C until 300 &#176;C. The total run time is 55 minutes per sample.</li>
		<li>Set the hot jet temperature to be 100 &#176;C higher than the oven temperature at any point in time. Thus: set the initial hot jet temperature to 160 &#176;C with a ramp rate of 5 &#176;C/min to 260 &#176;C, and then change the ramp rate to 4 &#176;C until 400 &#176;C.</li>
		<li>Set the ancillary liquid nitrogen Dewar connected to the GC to stay between 20% and 30% full during the run.</li>
	</ol>
	</li>
</ol>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td colspan="3">Instrument Parameters</td>
		</tr>
		<tr>
			<td>NCD</td>
			<td>Nitrogen Base Temperature</td>
			<td>280 &#176;C</td>
		</tr>
		<tr>
			<td></td>
			<td>Nitrogen Burner Temperature</td>
			<td>900 &#176;C</td>
		</tr>
		<tr>
			<td></td>
			<td>Hydrogen flow rate</td>
			<td>4 mL/min</td>
		</tr>
		<tr>
			<td></td>
			<td>Oxidizer flow rate (O2)</td>
			<td>8 mL/min</td>
		</tr>
		<tr>
			<td></td>
			<td>Data collection rate</td>
			<td>100 Hz</td>
		</tr>
		<tr>
			<td>Inlet</td>
			<td>Inlet Temperature</td>
			<td>300 &#176;C</td>
		</tr>
		<tr>
			<td></td>
			<td>Inlet liner</td>
			<td>Splitless</td>
		</tr>
		<tr>
			<td></td>
			<td>Purge flow to split vent</td>
			<td>15 mL/min</td>
		</tr>
		<tr>
			<td></td>
			<td>Septum Purge Flow</td>
			<td>3 mL/min</td>
		</tr>
		<tr>
			<td></td>
			<td>Carrier gas</td>
			<td>He</td>
		</tr>
		<tr>
			<td></td>
			<td>Carrier gas flow rate</td>
			<td>1.6 mL/min</td>
		</tr>
		<tr>
			<td></td>
			<td>Syringe size</td>
			<td>10 &#181;L</td>
		</tr>
		<tr>
			<td></td>
			<td>Injection volume</td>
			<td>1 &#181;L</td>
		</tr>
		<tr>
			<td>Modulator</td>
			<td>Modulation time</td>
			<td>6000 ms</td>
		</tr>
		<tr>
			<td></td>
			<td>Hot pulse duration</td>
			<td>375 ms</td>
		</tr>
		<tr>
			<td>Columns</td>
			<td>Flow</td>
			<td>1.6 mL/min</td>
		</tr>
		<tr>
			<td></td>
			<td>Flow type</td>
			<td>Constant flow</td>
		</tr>
	</tbody>
</table>
Table 2: Instrument parameters.
4. Instrument calibration
<ol>
	<li>Place the GC sample vials containing the prepared carbazole standards and load the previously configured method into the GC software.</li>
	<li>Create a sequence that aliquots the blank (isopropyl alcohol) at the beginning followed by the prepared carbazole standards by increasing concentration.</li>
	<li>Verify that the liquid nitrogen Dewar is between 20-30% full and all instrument parameters are in &#34;ready&#34; mode. Start the sequence.</li>
	<li>Once the calibration standard set analysis is completed, use the GCImage software to load each chromatogram, background correct, and detect each carbazole peak or blob. 
	NOTE: In GCImage, the detected peaks within the chromatogram are termed as &#34;blobs&#34; by the software.</li>
	<li>In a spreadsheet program, plot the response (blob volume) against the nitrogen concentration (ppm) of each calibration standard to create a calibration curve (see Figure 2). The trend line of the curve should have R2 &#8805; 0.99.</li>
</ol>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/60883/60883fig2.jpg" /> 
Figure 2: Example GCxGC-NCD carbazole calibration curve. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/60883/60883fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
5. Sample analysis
<ol>
	<li>Place the GC sample vials in the autosampler tray and load the previously configured method.</li>
	<li>Create a sequence that has a blank (isopropyl alcohol) at the beginning and then every 5 subsequent samples to limit any build-up of fuel within the columns.</li>
	<li>Verify that enough liquid nitrogen is available in the modulator&#39;s Dewar and that all instrument parameters are in &#34;ready&#34; mode. Then, start the sequence.</li>
</ol>
6. Data analysis
<ol>
	<li>Open the chromatogram in the GCImage software for data analysis and perform a background correction</li>
	<li>Detect blobs using the following filter parameters: 
	Minimum area = 25 
	Minimum volume = 0 
	Minimum peak = 25 
	NOTE: These parameters are subject to change based on instrument response or sample matrix.</li>
	<li>Use the GCImage template function to create or load a template to group nitrogen compound classes based on the elution times of the known standards (see Table 1). 
	NOTE: Further explanation of template usage can be found in the representative results and Figure 8.</li>
	<li>Once the compounds have been grouped, export the &#34;blob set table&#34; into a spreadsheet program. Use the sum the volume of all blobs/peaks within each compound class group, and the calibration equation determined in Section 4.4 to calculate the concentration in ppm for the nitrogen compounds in each group.</li>
	<li>If desired, use the following density calculations to correct for differences in the injection volume of sample vs. standards for quantitation: 
	<img src="/files/ftp_upload/60883/60883eq2a.jpg" /> 
	NOTE: *percent difference between the ng N injected in the sample matrix vs. the standard matrix</li>
	<li>Sum all nitrogen content in each compound class to obtain the total nitrogen content of the sample, if desired. If the total nitrogen content is determined to be above 150 ppm nitrogen or a compound class bin is outside of the calibration range, dilute the sample further for analysis. Compare these results with total nitrogen content as determined by ASTM D462913 for quantification verification.</li>
</ol>

<ol>
	<li>Garner, M. W., Morris, R. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laboratory+Studies+of+Good+Hope+and+Other+Diesel+Fuel+Samples.">Laboratory Studies of Good Hope and Other Diesel Fuel Samples.</a> ARTECH Corp. Report No. J8050.93-FR. , (1982).</li><li>Morris, R. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fleet+Fuel+Stability+Analyses+and+Evaluations.">Fleet Fuel Stability Analyses and Evaluations.</a> ARTECH Corp. Report No. DTNSRDC-SME-CR-01083. , (1983).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+F-76+Fuels+from+the+Western+Pacific+Region+Sampled+in+2014.">Analysis of F-76 Fuels from the Western Pacific Region Sampled in 2014.</a> Naval Research Laboratory Letter Report 6180/0012A. , (2015).</li><li>Westbrook, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+F-76+Fuel,+Sludge,+and+Particulate+Contamination.">Analysis of F-76 Fuel, Sludge, and Particulate Contamination.</a> Southwest Research Institute Letter Report. Project No. 08.15954.14.001. , (2015).</li><li>Morris, R. E., Loegel, T. N., Cramer, J. A., Leska Myers, K. M., A, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Examination+of+Diesel+Fuels+and+Insoluble+Gums+in+Retain+Samples+from+the+West+Coast-Hawaii+Region.">Examination of Diesel Fuels and Insoluble Gums in Retain Samples from the West Coast-Hawaii Region.</a> Naval Research Laboratory Memorandum Report. No. NRL/MR/6180-15-9647. , (2015).</li><li>Maciel, G. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantification+of+Nitrogen+Compounds+in+Diesel+Fuel+Samples+by+Comprehensive+Two-Dimensional+Gas+Chromatography+Coupled+with+Quadrupole+Mass+Spectrometry.">Quantification of Nitrogen Compounds in Diesel Fuel Samples by Comprehensive Two-Dimensional Gas Chromatography Coupled with Quadrupole Mass Spectrometry.</a> Journal of Separation Science. 38 (23), 4071-4077 (2015).</li><li>Deese, R. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+Organic+Nitrogen+Compounds+and+Their+Impact+on+the+Stability+of+Marginally+Stable+Diesel+Fuels.">Characterization of Organic Nitrogen Compounds and Their Impact on the Stability of Marginally Stable Diesel Fuels.</a> Energy &amp; Fuels. 33 (7), 6659-6669 (2019).</li><li>Lissitsyna, K., Huertas, S., Quintero, L. C., Polo, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+Simple+Method+for+Quanitation+of+Nitrogen+Compounds+in+Middle+Distillates+using+Solid+Phase+Extraction+and+Comprehensive+Two-Dimensional+Gas+Chromatography.">Novel Simple Method for Quanitation of Nitrogen Compounds in Middle Distillates using Solid Phase Extraction and Comprehensive Two-Dimensional Gas Chromatography.</a> Fuel. 104, 752-757 (2013).</li><li>Machado, M. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comprehensive+two-dimensional+gas+chromatography+for+the+analysis+of+nitrogen-containing+compounds+in+fossil+fuels:+A+review.">Comprehensive two-dimensional gas chromatography for the analysis of nitrogen-containing compounds in fossil fuels: A review.</a> Talanta. 198, 263-276 (2019).</li><li>Adam, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+Benchmark+for+Basic+and+Neutral+Nitrogen+Compounds+Speciation+in+Middle+Distillates+using+Comprehensive+Two-Dimensional+Gas+Chromatography.">New Benchmark for Basic and Neutral Nitrogen Compounds Speciation in Middle Distillates using Comprehensive Two-Dimensional Gas Chromatography.</a> Journal of Chromatography A. 1148, 55-65 (2007).</li><li>Wang, F. C. Y., Robbins, W. K., Greaney, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Speciation+of+Nitrogen-Containing+Compounds+in+Diesel+Fuel+by+Comprehensive+Two-Dimensional+Gas+Chromatography.">Speciation of Nitrogen-Containing Compounds in Diesel Fuel by Comprehensive Two-Dimensional Gas Chromatography.</a> Journal of Separation Science. 27, 468-472 (2004).</li><li>Yan, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sulfur+and+Nitrogen+Chemiluminescence+Detection+in+Gas+Chromatographic+Analaysis.">Sulfur and Nitrogen Chemiluminescence Detection in Gas Chromatographic Analaysis.</a> Journal of Chromatography A. 976 (1), 3-10 (2002).</li></ol>

The authors have nothing to disclose.

The purpose of this method is to provide detailed information on the nitrogen content of diesel and jet fuels without extensive sample preparation such as liquid extractions. This is achieved by pairing a two dimensional GC system (GCxGC) with a nitrogen-specific detector (nitrogen chemiluminescence detector, NCD). The GCxGC provides significant separation of the compounds relative to traditional one-dimensional GC. The NCD provides trace nitrogen compound detection without any background interferences. Other nitrogen-sp...

Before use, fuels undergo extensive quality assurance and specification testing by refineries to verify that the fuel they are producing will not fail or cause equipment problems once disseminated. These specification tests include flash point verification, freeze point, storage stability, and many more. The storage stability tests are important as they determine if the fuels have a tendency to undergo degradation during storage, resulting in the formation of gums or particulates. There have been incidences in the past when F-76 diesel fuels have failed during storage even though they passed all specification tests1. These failures resulted in high concentrations of particulate matter in the fuels that could be detrimental to equipment such as fuel pumps. The extensive research investigation that followed this discovery suggested that there is a causal relationship between certain types of nitrogen compounds and the particulate formation2,3,4,5. However, many of the techniques used to measure nitrogen content are strictly qualitative, require extensive sample preparation, and provide little information on the identity of the suspect nitrogen compounds. The method described herein is a two-dimensional GC (GCxGC) method paired with a nitrogen chemiluminescence detector (NCD) that was developed for the purpose of characterizing and quanitifying trace nitrogen compounds in diesel and jet fuels.
Gas chromatography is used extensively in petroleum analyses and there are over sixty published ASTM petroleum methods associated with the technique. A wide range of detectors are combined with gas chromatography such as mass spectrometry (MS, ASTM D27896, D57697), Fourier-transform infrared spectroscopy (FTIR, D59868), vacuum ultraviolet spectroscopy (VUV, D80719), flame ionization detector (FID, D742310), and chemiluminesence detectors (D550411, D780712, D4629-1713). All these methods can provide significant compositional information about a fuel product. Since fuels are complex sample matrices, gas chromatography enhances compositional analysis by separating out sample compounds based on boiling point, polarity, and other interactions with the column.
To further this separation ability, two-dimensional gas chromatography (GCxGC) methods can be utilized to provide compositional maps by using sequential columns with orthogonal column chemistries. Separation of compounds occur both by polarity and boiling point, which is a comprehensive means to isolate fuel constituents. Although it is possible to analyze nitrogen-containing compounds with GCxGC-MS, the trace concentration of the nitrogen compounds within the complex sample inhibits identification14. Liquid-liquid phase extractions have been attempted in order to use GC-MS techniques; however, it was found that the extractions are incomplete and exclude important nitrogen compounds15. Additionally, others have used solid phase extraction to enhance the nitrogen signal while reducing the potential for the fuel sample matrix interference16. However, this technique has been found to irreversible retail certain nitrogen species, especially low molecular weight nitrogen-bearing species.
The nitrogen chemiluminescence detector (NCD) is a nitrogen-specific detector and has been successfully used for fuel analyses17,18,19. It utilizes a combustion reaction of nitrogen-containing compounds, the formation of nitric oxide (NO), and a reaction with ozone (see Equations 1 &#38; 2)20. This is accomplished in a quartz reaction tube that contains a platinum catalyst and is heated to 900 &#176;C in the presence of oxygen gas.
The photons emitted from this reaction are measured with a photomultiplier tube. This detector has a linear and equimolar response to all nitrogen-containing compounds because all nitrogen-containing compounds are converted to NO. It is also not prone to matrix effects because other compounds in the sample are converted to non-chemiluminescence species (CO2 and H2O) during the conversion step of the reaction (Equation 1). Thus, it is an ideal method for measuring nitrogen compounds in a complex matrix such as fuels.
<img src="/files/ftp_upload/60883/60883eq1a.jpg" />
The equimolar response of this detector is important for nitrogen compound quantitation in fuels because the complex nature of fuels does not allow for calibration of each nitrogen analyte. The selectivity of this detector facilitates the detection of trace nitrogen compounds even with a complex hydrocarbon background.

<table><tbody><tr><td>10 &amp;micro;L syringe</td><td>Agilent</td><td></td><td>gold series</td></tr><tr><td>180 &amp;micro;m x 0.18 &amp;micro;m Secondary Column</td><td>Restek</td><td>Rxi-1MS</td><td>nonpolar phase column, crossbond dimethyl polysiloxane</td></tr><tr><td>250 &amp;micro;m x 0.25 &amp;micro;m Primary Column</td><td>Restek</td><td>Rxi-17SilMS</td><td>midpolarity phase column</td></tr><tr><td>Autosampler tray and tower</td><td>Agilent</td><td>7963A</td><td></td></tr><tr><td>Carbazole</td><td>Sigma</td><td>C5132</td><td>98%</td></tr><tr><td>Diethylaniline</td><td>Aldrich</td><td>185898</td><td>&amp;ge; 99%</td></tr><tr><td>Dimethylindole</td><td>Aldrich</td><td>D166006</td><td>97%</td></tr><tr><td>Duel Loop Thermal Modulator</td><td>Zoex Corporation</td><td>ZX-1</td><td></td></tr><tr><td>Ethylcarbazole</td><td>Aldrich</td><td>E16600</td><td>97%</td></tr><tr><td>Gas chromatograph</td><td>Agilent</td><td>7890B</td><td></td></tr><tr><td>GC vials</td><td>Restek</td><td>21142</td><td></td></tr><tr><td>GCImage Software, Version 2.6</td><td>Zoex Corporation</td><td></td><td></td></tr><tr><td>Indole</td><td>Aldrich</td><td>13408</td><td>&amp;ge; 99%</td></tr><tr><td>Isopropyl Alcohol</td><td>Fisher Scientific</td><td>A461-500</td><td>Purity 99.9%</td></tr><tr><td>Methylaniline</td><td>Aldrich</td><td>236233</td><td>&amp;ge; 99%</td></tr><tr><td>Methylquinoline</td><td>Aldrich</td><td>382493</td><td>99%</td></tr><tr><td>Nitrogen Chemiluminescence Detector</td><td>Agilent</td><td>8255</td><td></td></tr><tr><td>Pyridine</td><td>Sigma-Aldrich</td><td>270970</td><td>anhydrous, 99.8%</td></tr><tr><td>Quinoline</td><td>Aldrich</td><td>241571</td><td>98%</td></tr><tr><td>Trimethylamine</td><td>Sigma-Aldrich</td><td>243205</td><td>anhydrous, &amp;ge; 99%</td></tr></tbody></table>

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.

The nitrogen-containing compound, carbazole, was used in this method as the calibration standard. Carbazole elutes at approximately 33 min from the primary column and at 2 s from the secondary column. These elution times will vary slightly depending on the exact column length and instrumentation. In order to obtain a proper calibration curve and, subsequently, good quantitation of nitrogen compounds within a sample, the calibration peaks should not be overloaded nor have any nitrogen cont...

Watch this Scientific Journal Video about Nitrogen Compound Characterization in Fuels by Multidimensional Gas Chromatography at JoVE.com

Nitrogen Compound Characterization in Fuels by Multidimensional Gas Chromatography

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 ...

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Unit 1

Principles of Chromatography

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7.5K Views.  U.S. Naval Research Laboratory. 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.

Video: Nitrogen Compound Characterization in Fuels by Multidimensional Gas Chromatography

Measurement of H2S in Crude Oil and Crude Oil Headspace Using Multidimensional Gas Chromatography, Deans Switching and Sulfur-selective Detection

A method for the analysis of dissolved hydrogen sulfide in crude oil samples is demonstrated using gas chromatography. In order to effectively eliminate interferences, a two dimensional column configuration is used, with a Deans switch employed to transfer hydrogen sulfide from the first to the second column (heart-cutting). Liquid crude samples are first separated on a dimethylpolysiloxane column, and light gases are heart-cut and further separated on a bonded porous layer open tubular (PLOT) column that is able to separate hydrogen sulfide from other light sulfur species. Hydrogen sulfide is then detected with a sulfur chemiluminescence detector, adding an additional layer of selectivity. Following separation and detection of hydrogen sulfide, the system is backflushed to remove the high-boiling hydrocarbons present in the crude samples and to preserve chromatographic integrity. Dissolved hydrogen sulfide has been quantified in liquid samples from 1.1 to 500 ppm, demonstrating wide applicability to a range of samples. The method has also been successfully applied for the analysis of gas samples from crude oil headspace and process gas bags, with measurement from 0.7 to 9,700 ppm hydrogen sulfide.

Measurement of H2S in Crude Oil and Crude Oil Headspace Using Multidimensional Gas Chromatography, Deans Switching and Sulfur-selective Detection

A multidimensional gas chromatography method for the analysis of dissolved hydrogen sulfide in liquid crude oil samples is presented. A Deans switch is used to heart-cut light sulfur gases for separation on a secondary column and detection on a sulfur chemiluminescence detector.

A method for the analysis of dissolved hydrogen sulfide in crude oil samples is demonstrated using gas chromatography. In order to effectively eliminate ...

Environment

Automated, High-resolution Mobile Collection System for the Nitrogen Isotopic Analysis of NOx

Nitrogen oxides (NOx = NO + NO2) are a family of atmospheric trace gases that have great impact on the environment. NOx concentrations directly influence the oxidizing capacity of the atmosphere through interactions with ozone and hydroxyl radicals. The main sink of NOx is the formation and deposition of nitric acid, a component of acid rain and a bioavailable nutrient. NOx is emitted from a mixture of natural and anthropogenic sources, which vary in space and time. The collocation of multiple sources and the short lifetime of NOx make it challenging to quantitatively constrain the influence of different emission sources and their impacts on the environment. Nitrogen isotopes of NOx have been suggested to vary amongst different sources, representing a potentially powerful tool to understand the sources and transport of NOx. However, previous methods of collecting atmospheric NOx integrate over long (week to month) time spans and are not validated for the efficient collection of NOx in relevant, diverse field conditions. We report on a new, highly efficient field-based system that collects atmospheric NOx for isotope analysis at a time resolution between 30 min and 2 hr. This method collects gaseous NOx in solution as nitrate with 100% efficiency under a variety of conditions. Protocols are presented for collecting air in urban settings under both stationary and mobile conditions. We detail the advantages and limitations of the method and demonstrate its application in the field. Data from several deployments are shown to 1) evaluate field-based collection efficiency by comparisons with in situ NOx concentration measurements, 2) test the stability of stored solutions before processing, 3) quantify in situ reproducibility in a variety of urban settings, and 4) demonstrate the range of N isotopes of NOx detected in ambient urban air and on heavily traveled roadways.

Automated, High-resolution Mobile Collection System for the Nitrogen Isotopic Analysis of NOx

Previous work suggests that the nitrogen isotopic composition of atmospheric nitrogen oxides might distinguish the influence of different sources in the environment. We report on an automated, mobile, field-based method for the high collection efficiency of atmospheric NOx for N isotopic analysis at an hourly time resolution.

Nitrogen oxides (NOx = NO + NO2) are a family of atmospheric trace gases that have great impact on the environment. NOx concentrations directly influence ...

On-line Analysis of Nitrogen Containing Compounds in Complex Hydrocarbon Matrixes

The shift to heavy crude oils and the use of alternative fossil resources such as shale oil are a challenge for the petrochemical industry. The composition of heavy crude oils and shale oils varies substantially depending on the origin of the mixture. In particular they contain an increased amount of nitrogen containing compounds compared to the conventionally used sweet crude oils. As nitrogen compounds have an influence on the operation of thermal processes occurring in coker units and steam crackers, and as some species are considered as environmentally hazardous, a detailed analysis of the reactions involving nitrogen containing compounds under pyrolysis conditions provides valuable information. Therefore a novel method has been developed and validated with a feedstock containing a high nitrogen content, i.e., a shale oil. First, the feed was characterized offline by comprehensive two-dimensional gas chromatography (GC &#215; GC) coupled with a nitrogen chemiluminescence detector (NCD). In a second step the on-line analysis method was developed and tested on a steam cracking pilot plant by feeding pyridine dissolved in heptane. The former being a representative compound for one of the most abundant classes of compounds present in shale oil. The composition of the reactor effluent was determined via an in-house developed automated sampling system followed by immediate injection of the sample on a GC &#215; GC coupled with a time-of-flight mass spectrometer (TOF-MS), flame ionization detector (FID) and NCD. A novel method for quantitative analysis of nitrogen containing compounds using NCD and 2-chloropyridine as an internal standard has been developed and demonstrated.

A method combining comprehensive two-dimensional gas chromatography with nitrogen chemiluminescence detection has been developed and applied to on-line analysis of nitrogen containing compounds in a complex hydrocarbon matrix.

The shift to heavy crude oils and the use of alternative fossil resources such as shale oil are a challenge for the petrochemical industry. The ...

Single-throughput Complementary High-resolution Analytical Techniques for Characterizing Complex Natural Organic Matter Mixtures

Natural organic matter (NOM) is composed of a highly complex mixture of thousands of organic compounds which, historically, proved difficult to characterize. However, to understand the thermodynamic and kinetic controls on greenhouse gas (carbon dioxide [CO2] and methane [CH4]) production resulting from the decomposition of NOM, a molecular-level characterization coupled with microbial proteome analyses is necessary. Further, climate and environmental changes are expected to perturb natural ecosystems, potentially upsetting complex interactions that influence both the supply of organic matter substrates and the microorganisms performing the transformations. A detailed molecular characterization of the organic matter, microbial proteomics, and the pathways and transformations by which organic matter is decomposed will be necessary to predict the direction and magnitude of the effects of environmental changes. This article describes a methodological throughput for comprehensive metabolite characterization in a single sample by direct injection Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), gas chromatography mass spectrometry (GC-MS), nuclear magnetic resonance (NMR) spectroscopy, liquid chromatography mass spectrometry (LC-MS), and proteomics analysis. This approach results in a fully-paired dataset which improves statistical confidence for inferring pathways of organic matter decomposition, the resulting CO2 and CH4 production rates, and their responses to environmental perturbation. Herein we present results of applying this method to NOM samples collected from peatlands; however, the protocol is applicable to any NOM sample (e.g., peat, forested soils, marine sediments, etc.).

This protocol describes a single throughput for complementary analytical and omics techniques culminating in a fully-paired characterization of natural organic matter and microbial proteomics in different ecosystems. This approach permits robust comparisons for identifying metabolic pathways and transformations important for describing greenhouse gas production and predicting responses to environmental change.

Natural organic matter (NOM) is composed of a highly complex mixture of thousands of organic compounds which, historically, proved difficult to ...

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 ...

Qualitative Characterization of the Aqueous Fraction from Hydrothermal Liquefaction of Algae Using 2D Gas Chromatography with Time-of-flight Mass Spectrometry

Two-dimensional gas chromatography coupled with time-of-flight mass spectrometry is a powerful tool for identifying and quantifying chemical components in complex mixtures. It is often used to analyze gasoline, jet fuel, diesel, bio-diesel and the organic fraction of bio-crude/bio-oil. In most of those analyses, the first dimension of separation is non-polar, followed by a polar separation. The aqueous fractions of bio-crude and other aqueous samples from biofuels production have been examined with similar column combinations. However, sample preparation techniques such as derivatization, solvent extraction, and solid-phase extraction were necessary prior to analysis. In this study, aqueous fractions obtained from the hydrothermal liquefaction of algae were characterized by two-dimensional gas chromatography coupled with time-of-flight mass spectrometry without prior sample preparation techniques using a polar separation in the first dimension followed by a non-polar separation in the second. Two-dimensional plots from this analysis were compared with those obtained from the more traditional column configuration. Results from qualitative characterization of the aqueous fractions of algal bio-crude are discussed in detail. The advantages of using a polar separation followed by a non-polar separation for characterization of organics in aqueous samples by two-dimensional gas chromatography coupled with time-of-flight mass spectrometry are highlighted.

A two-dimensional gas chromatography-time-of-flight mass spectrometry method is described for characterization of the aqueous fraction of bio-crude produced from hydrothermal liquefaction of algae. This protocol can also be employed to analyze the aqueous fraction of liquid products from fast pyrolysis, catalytic fast pyrolysis, catalytic deoxygenation and hydro-treating.

Two-dimensional gas chromatography coupled with time-of-flight mass spectrometry is a powerful tool for identifying and quantifying chemical components in ...

Bioengineering

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).

Data processing and evaluation are critical steps of comprehensive two-dimensional gas chromatography (GCxGC), particularly when coupled to mass ...

Gas Chromatography (GC) with Flame-Ionization Detection

Source: Laboratory of Dr. B. Jill Venton - University of Virginia
Gas chromatography (GC) is used to separate and detect small molecular weight compounds in the gas phase. The sample is either a gas or a liquid that is vaporized in the injection port. Typically, the compounds analyzed are less than 1,000 Da, because it is difficult to vaporize larger compounds. GC is popular for environmental monitoring and industrial applications because it is very reliable and can be run nearly continuously. GC is typically used in applications where small, volatile molecules are detected and with non-aqueous solutions. Liquid chromatography is more popular for measurements in aqueous samples and can be used to study larger molecules, because the molecules do not need to vaporize. GC is favored for nonpolar molecules while LC is more common for separating polar analytes.
The mobile phase for gas chromatography is a carrier gas, typically helium because of its&#160;low molecular weight and being chemically inert. Pressure is applied and the mobile phase moves the analyte through the column. The separation is accomplished using a column coated with a stationary phase. Open tubular capillary columns are the most popular columns and have the stationary phase coated on the walls of the capillary. Stationary phases are often derivatives of polydimethylsiloxane, with 5&#8211;10% of the groups functionalized to tune the separation. Typical functional groups are phenyl, cyanopropyl, or trifluoropropyl groups. Capillary columns are usually 5&#8211;50 m&#160;long. Narrower columns have higher resolution but require higher pressures. Packed columns can also be used where the stationary phase is coated onto beads packed in the column. Packed columns are shorter, 1&#8211;5 m. Open tubular capillaries are generally preferred because they allow higher efficiencies, faster analyses, and have higher capacities.
Flame-ionization detection (FID) is a good general detector for organic compounds in GC that detects the amount of carbon in a sample. After the column, samples are burned in a hot, hydrogen-air flame. Carbon ions are produced by the combustion. While the overall efficiency of the process is low (only 1 in 105 carbon ions produce an ion in the flame) the total amount of ions is directly proportional to the amount of carbon in the sample. Electrodes are used to measure the current from the ions. FID is a destructive detector, as the entire sample is pyrolyzed. FID is unaffected by noncombustible gases and water.

Gas Chromatography GC with Flame-Ionization Detection

Source: Laboratory of Dr. B. Jill Venton - University of Virginia
Gas chromatography (GC) is used to separate and detect small molecular weight compounds ...

JoVE Science Education

Carbon and Nitrogen Analysis of Environmental Samples

Source: Laboratories of Margaret Workman and Kimberly Frye - Depaul University
Elemental Analysis is a method used to determine elemental composition of a material. In environmental samples such as soils, scientists are particularly interested in the amounts of two ecologically important elements, nitrogen and carbon. Elemental analysis by the flash combustion technique works by oxidizing the sample with a catalyst through combustion in a high-temperature chamber. The products of combustion are then reduced to N2 and CO2 and detected with a thermal conductivity detector.
Unlike other methods for total nitrogen determination (Kjeldahl method) and total carbon determination (Walkley-Black, Heanes or Leco methods), the flash combustion technique does not use toxic chemicals and is therefore much safer to use.
This video will demonstrate combustion-based elemental analysis using the Flash EA 1112 instrument from Thermo Fisher Scientific.

Source: Laboratories of Margaret Workman and Kimberly Frye - Depaul University
Elemental Analysis is a method used to determine elemental composition of a ...

Environmental Sciences

Environmental Science

Gas Chromatography&ndash;Mass Spectrometry (GC&ndash;MS)

Gas chromatography&#8211;mass spectrometry (GC&#8211;MS) is the combination of analytical techniques of gas chromatography and mass spectrometry in a single instrument for analyzing a mixture of compounds. The gas chromatograph separates the compounds in the mixture, and the mass spectrometer analyzes each compound separately to determine the molecular masses and molecular structures.
A gas chromatograph consists of a long, narrow capillary column with a polysiloxane coating on the inner wall. The coating material features a high boiling point, low viscosity, and low polarity and functions as the stationary phase of the chromatograph. The analyte is injected into one end of the column and flushed through the column using an inert gas flow as the mobile phase. The boiling point of each compound and its interaction with the stationary phase determines the speed of movement through the column. Consequently, each compound in the mixture reaches the other end of the column at a different time. Eventually, the mass spectrometer connected to the column&#39;s end analyzes each compound separately.

Gas Chromatography&amp;#8211;Mass Spectrometry GC&amp;#8211;MS

Gas chromatography&#8211;mass spectrometry (GC&#8211;MS) is the combination of analytical techniques of gas chromatography and mass spectrometry in a ...

Nitrogen Compound Characterization in Fuels by Multidimensional Gas Chromatography

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Measurement of H₂S in Crude Oil and Crude Oil Headspace Using Multidimensional Gas Chromatography, Deans Switching and Sulfur-selective Detection

Automated, High-resolution Mobile Collection System for the Nitrogen Isotopic Analysis of NO_x