Name: gas chromatography-mass spectrometry paired with total vaporization solid-phase microextraction as a forensic tool
Uploaded: 2021-05-25T13:00:00.000+00:00
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Description: Watch this Scientific Journal Video about Gas Chromatography-Mass Spectrometry Paired with Total Vaporization Solid-Phase Microextraction as a Forensic Tool at JoVE.com

This research was supported by the National Institute of Justice (Award No. 2015-DN-BX-K058 &#38; 2018-75-CX-0035). The opinions, findings, and conclusions expressed here are those of the author and do not necessarily reflect those of the funding organizations.

1. General TV-SPME sample preparation and GC-MS analysis
NOTE: If the sample is already dissolved in a matrix, skip to Step 1.2.
<ol>
	<li>Extract or dissolve the solid sample in enough solvent (water, methanol, acetone, etc.) to reach the desired concentration. Liquid samples can be used &#8220;as is&#8221;. 
	NOTE: The amount of solid sample used depends on the desired concentration of the sample. Concentrations below 1 ppm (w/v) are recommended to avoid overloading the GC column. Analyte should be soluble in chosen organic solvent.
	<ol>
		<li>Ensure that the sample has fully dissolved.</li>
	</ol>
	</li>
	<li>Calculate the volume needed to fully vaporize the sample using Equation 3 at the chosen temperature. For example, if the experiment is to be performed at 60 &#176;C, calculate the volume needed to completely vaporize the solvent at 60 &#176;C.
	<ol>
		<li>Transfer this sample volume into a headspace vial and secure the cap. Acceptable methods for transferring liquid samples at the microliter scale include manually via glass syringe, an electronic glass syringe, or an autosampler robot capable of liquid transfers for sample preparation.</li>
	</ol>
	</li>
	<li>If derivatizing the sample, prepare the proper derivatization agent by placing ~1 mL of the agent into a headspace vial.
	<ol>
		<li>Choose the derivatization agent based on the type of derivatization needed: alkylation, acylation, or silyation. In this case, the recommended derivatization agent for the carboxylic acid and alcohol functional groups found on GHB is O-bis(trimethylsilyl) trifluoroacetamide (BSTFA). The derivatization agent may be used &#8220;as is&#8221; and does not require dilution. One mL of derivatization agent is enough to ensure complete saturation of the SPME fiber. 
		CAUTION: Derivatization agents are toxic and should be handled in a fume hood.</li>
	</ol>
	</li>
	<li>Set the proper incubation/extraction temperature based upon the calculation in step 1.2. This temperature ensures total vaporization, sufficient sample extraction, and complete derivatization (if necessary).
	<ol>
		<li>Select GC-MS parameters (oven temperature program, flow rate, inlet temperature, etc.) based on the class of the compound(s) of interest. See Step 3 for an example parameter set.</li>
		<li>Ensure that the proper inlet liner (e.g., 2 mm inner diameter or less) is in the GC inlet.</li>
	</ol>
	</li>
	<li>Ensure the SPME fiber has been properly conditioned and is in good working condition before beginning the analysis.
	<ol>
		<li>Vary the conditioning parameters based on the type of SPME fiber being used. Please see SPME fiber instructions for proper conditioning temperature and time. In general, analyzing several SPME fiber blanks until they are reproducible is sufficient to characterize a SPME fiber as fully conditioned.</li>
	</ol>
	</li>
</ol>
2. Gamma-hydroxybutyrate (GHB) and Gamma-butyrolactone (GBL) sample preparation
<ol>
	<li>Prepare a sample of GHB and/or GBL in water with a concentration of less than 1 ppm.</li>
	<li>Transfer 1 &#181;L of this sample to a 20 mL headspace vial using one of the methods described in 1.2.1.
	<ol>
		<li>Note that that the analysis of aqueous samples requires the lowest sample volumes. For example, one &#181;L of water will completely vaporize into a 20 mL headspace vial at 60 &#176;C.</li>
		<li>Cap the vial immediately.</li>
	</ol>
	</li>
	<li>Place ~1 mL of BSTFA + 1% trimethylchlorosilane (TMCS) into a separate 20 mL headspace vial and cap. 
	NOTE: GBL does not derivatize. A derivatization step is still required, however, is to ensure the water solvent derivatizes and does not interfere with the sample. 
	CAUTION: BSTFA is toxic and should be handled in a fume hood.</li>
</ol>
3. GC-MS parameters and setup for GHB and GBL in water
<ol>
	<li>Create a method using the following GC-MS parameters: 
	Initial oven temperature: 60 &#176;C held for 1 minute. 
	Oven program: 15 &#176;C/minute. 
	Final oven temperature: 280 &#176;C, held for 1 minute. 
	Flow rate: 2.5 mL/minute (speed optimized flow for a 0.25 mm i.d. column). 
	Inlet temperature: 250 &#176;C. 
	Transfer line temperature: 280 &#176;C.</li>
	<li>Ensure a narrow (2 mm i.d. or less) SPME inlet liner has been placed inside the GC inlet.</li>
	<li>Ensure the PDMS/DVB SPME fiber has been properly conditioned and is in good working order prior to analysis. 
	NOTE: PDMS/DVB SPME fibers should be conditioned in the GC inlet at 250 &#176;C for 30 minutes. PDMS/DVB SPME fibers should be an off-white color.</li>
	<li>Run the GC-MS on the sample.</li>
</ol>

<ol>
	<li>Pawliszyn, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Method+and+Device+for+Solid+Phase+Microextraction+and+Desorption.">Method and Device for Solid Phase Microextraction and Desorption.</a> United States patent. , (2005).</li><li>Pawliszyn, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Solid phase microextraction: theory and practice. , (1997).</li><li>Rainey, C. L., Bors, D. E., Goodpaster, J. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+and+optimization+of+a+total+vaporization+technique+coupled+to+solid-phase+microextraction.">Design and optimization of a total vaporization technique coupled to solid-phase microextraction.</a> Analytical Chemistry. 86 (22), 11319-11325 (2014).</li><li>Sinnott, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Chemical Engineering Design: Chemical Engineering. 6, (2005).</li><li>Davis, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Detection of Illicit Drugs in Various Matrices Via Total Vaporization Solid-Phase Microextraction (TV-SPME). , (2019).</li><li>Ash, J., Hickey, L., Goodpaster, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formation+and+identification+of+novel+derivatives+of+primary+amine+and+zwitterionic+drugs.">Formation and identification of novel derivatives of primary amine and zwitterionic drugs.</a> Forensic Chemistry. 10, 37-47 (2018).</li><li>Sauzier, G., Bors, D., Ash, J., Goodpaster, J. V., Lewis, S. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimisation+of+recovery+protocols+for+double-base+smokeless+powder+residues+analysed+by+total+vaporisation+(TV)+SPME/GC-MS.">Optimisation of recovery protocols for double-base smokeless powder residues analysed by total vaporisation (TV) SPME/GC-MS.</a> Talanta. 158, 368-374 (2016).</li><li>Bors, D., Goodpaster, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mapping+smokeless+powder+residue+on+PVC+pipe+bomb+fragments+using+total+vaporization+solid+phase+microextraction.">Mapping smokeless powder residue on PVC pipe bomb fragments using total vaporization solid phase microextraction.</a> Forensic science international. 276, 71-76 (2017).</li><li>Bors, D., Goodpaster, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+analysis+of+racing+fuels+using+total+vaporization+and+gas+chromatography+mass+spectrometry+(GC/MS).">Chemical analysis of racing fuels using total vaporization and gas chromatography mass spectrometry (GC/MS).</a> Analytical Methods. 8 (19), 3899-3902 (2016).</li><li>Beiranvand, M., Ghiasvand, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+and+optimization+of+the+VA-TV-SPME+method+for+ultrasensitive+determination+of+the+PAHs+in+polluted+water.">Design and optimization of the VA-TV-SPME method for ultrasensitive determination of the PAHs in polluted water.</a> Talanta. 212, 120809 (2020).</li></ol>

The authors have nothing to disclose.

TV-SPME has some benefits over liquid injection GC in that large sample sizes (e.g., 100 &#181;L) may be used without instrument modifications. TV-SPME also has some of the same benefits as headspace SPME. Headspace SPME does not require any extraction or filtration because any nonvolatile compounds will remain in the headspace vial and will not be adsorbed onto the fiber, yielding a clean sample. This method also helps to eliminate matrix effects due to this being a two-phase system (headspace and fiber) as opposed to a...

Solid-Phase Microextraction (SPME) is a sampling technique in which a liquid or solid sample is placed into a headspace vial and a SPME fiber, coated with a polymeric material, is then introduced into the sample headspace (or immersed in a liquid sample). The analyte is sorbed onto the fiber and then the fiber is placed inside the GC inlet for desorption1,2. Total Vaporization Solid-Phase Microextraction (TV-SPME) is a similar technique as immersion SPME but completely vaporizes a liquid sample before analytes are adsorbed onto the fiber. This allows for partitioning of the analyte between only the solvent vapor and the coating of the fiber, allowing for more of the analyte to be adsorbed onto the fiber and resulting in good sensitivity3. There are various SPME fibers available and the fiber should be chosen based on the analyte of interest, solvent/matrix, and derivatization agent. See Table 1 for established TV-SPME analytes.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Sample</td>
			<td>Analyte(s)</td>
			<td>Recommended SPME Fiber</td>
			<td>Reference(s)</td>
		</tr>
		<tr>
			<td>Human Hair</td>
			<td>Nicotine, cotinine</td>
			<td>Polydimethylsiloxane/divinylbenzene (PDMS/DVB), polyacrylate (PA)</td>
			<td>3</td>
		</tr>
		<tr>
			<td>Smokeless Powder</td>
			<td>Nitroglycerin, diphenylamine</td>
			<td>Polydimethylsiloxane (PDMS), polyethylene glycol (PEG)</td>
			<td>7, 8</td>
		</tr>
		<tr>
			<td>Racing fuel</td>
			<td>Methanol, nitromethane</td>
			<td>PEG</td>
			<td>9</td>
		</tr>
		<tr>
			<td>Water</td>
			<td>Polycyclic aromatic hydrocarbons</td>
			<td>PDMS</td>
			<td>10</td>
		</tr>
		<tr>
			<td>Beverages</td>
			<td>&#611;-Hydroxybutyric acid, &#611;-butyrolactone</td>
			<td>PDMS</td>
			<td>This Work</td>
		</tr>
		<tr>
			<td>Solid Powder</td>
			<td>Methamphetamine, amphetamine</td>
			<td>PDMS/DVB</td>
			<td>Unpublished</td>
		</tr>
	</tbody>
</table>
Table 1. Recommended SPME fibers with established TV-SPME analytes.
To perform TV-SPME, analytes are dissolved in a solvent and an aliquot of this mixture is placed into a headspace vial. Samples do not need to be filtered because only the solvent and volatile analytes will vaporize. Specific volumes of liquid samples must be used to ensure total vaporization of the sample. These volumes are determined by using the Ideal Gas Law to calculate the number of moles of a solvent multiplied by the molar volume of the liquid (Equation 1). 
<img alt="Equation 1" src="/files/ftp_upload/61880/61880equ01.jpg" /> Equation 1
where Vo is the volume of the sample (mL), P is the vapor pressure of the solvent (bar), Vv is the volume of the vial (L), R is the ideal gas constant (0.083145 <img alt="Equation 1" src="/files/ftp_upload/61880/61880equ04.jpg" />), M is the molar mass of the solvent (g/mol), T is temperature (K), and <img alt="Equation 5" src="/files/ftp_upload/61880/61880equ05.jpg" /> is the density of the solvent (g/mL).3
In order to use the correct vapor pressure, the Antoine equation (Equation 2) is used to account for the influence of temperature:4 
<img alt="Equation 2" src="/files/ftp_upload/61880/61880equ02.jpg" /> Equation 2
where T is temperature and A, B, and C are the Antoine constants for the solvent. Equation 2 may be substituted into Equation 1, yielding: 
<img alt="Equation 3" src="/files/ftp_upload/61880/61880equ03v2.jpg" /> Equation 3
Equation 3 gives the volume of the sample (Vo) that can be completely vaporized as a function of the temperature and solvent used.
To perform derivatization with TV-SPME, the SPME fiber is first exposed to a vial containing the derivatization agent for a predetermined amount of time depending on the analyte. The SPME fiber is then exposed to a new vial containing the analyte of interest. This vial is heated inside of a heated agitator. The analyte is then adsorbed onto the fiber with the derivatization agent. The derivatization of the analyte and/or the matrix takes place on the fiber before being inserted into the GC inlet for desorption. Figure 1 shows a depiction of the TV-SPME process with derivatization.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61880/61880fig01.jpg" /> 
Figure 1: Depiction of the TV-SPME process with derivatization.&#160;The SPME fiber first enters the derivatization vial where the derivatization agent (yellow circles) sorb onto the fiber. The fiber is then introduced to the sample (blue circles) and heated. Formation of the derivative (green circles) takes place on the fiber during the extraction time. <a href="https://www.jove.com/files/ftp_upload/61880/61880fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
TV-SPME is beneficial because it allows for the analyte to be derivatized during the extraction process which reduces analysis time. Other methods, such as liquid injection, require that the analyte react with the derivatizing agent in solution prior to being injected into the GC. TV-SPME also requires little to no sample preparation. A matrix containing an analyte may be placed directly into the headspace vial and analyzed. Many compounds of interest are compatible with TV-SPME. Compounds must be soluble in a solvent and sufficiently volatile to allow for vaporization. Additionally, compounds must be thermally stable to be analyzed by GC-MS. TV-SPME has been used to analyze drugs and drug metabolites, racing fuels, polycyclic aromatic hydrocarbons, and explosive materials3,5,6,7,8,9,10.

<table><tbody><tr><td>10 &amp;micro;L Syringe</td><td>Gerstel</td><td>100111-014-00</td><td></td></tr><tr><td>BSTFA + 1% TMCS (10 x 1 GM)</td><td>Regis Technologies Inc.</td><td>50442882</td><td></td></tr><tr><td>eVol XR Sample Dispensing System Kit</td><td>ThermoFisher Scientific</td><td>66002-024</td><td></td></tr><tr><td>&lt;img alt=&quot;Equation 6&quot; src=&quot;/files/ftp_upload/61880/61880equ06.jpg&quot;/&gt;-Butyrolactone (GBL)</td><td>Sigma-Aldrich</td><td>B103608-26G</td><td></td></tr><tr><td>&lt;img alt=&quot;Equation 7&quot; src=&quot;/files/ftp_upload/61880/61880equ06.jpg&quot;/&gt;-Hydroxy Butyric Acid (GHB)</td><td>Cayman Chemicals</td><td>9002506</td><td></td></tr><tr><td>Headspace Screw-Thread Vials, 18 mm</td><td>Restek</td><td>23083</td><td></td></tr><tr><td>Magnetic Screw-Thread Caps, 18 mm</td><td>Restek</td><td>23091</td><td></td></tr><tr><td>Optima water for HPLC</td><td>Fisher Chemical</td><td>W71</td><td></td></tr><tr><td>SPME Fiber Assembly Polydimethylsiloxane (PDMS)</td><td>Supelco</td><td>57341-U</td><td></td></tr><tr><td>SPME Fiber Assembly Polydimethylsiloxane/Divinylbenzene (PDMS/DVB)</td><td>Supelco</td><td>57293-U</td><td></td></tr><tr><td>Topaz 2.0 mm ID Straight Inlet Liner</td><td>Restek</td><td>23313</td><td></td></tr></tbody></table>

gas chromatography-mass spectrometry paired with total vaporization solid-phase microextraction as a forensic tool

Gas Chromatography &#8211; Mass Spectrometry (GC-MS) is a frequently used technique for the analysis of numerous analytes of forensic interest, including controlled substances, ignitable liquids, and explosives. GC-MS can be coupled with Solid-Phase Microextraction (SPME), in which a fiber with a sorptive coating is placed into the headspace above a sample or immersed in a liquid sample. Analytes are sorbed onto the fiber which is then placed inside the heated GC inlet for desorption. Total Vaporization Solid-Phase Microextraction (TV-SPME) utilizes the same technique as immersion SPME but immerses the fiber into a completely vaporized sample extract. This complete vaporization results in a partition between only the vapor phase and the SPME fiber without interference from a liquid phase or any insoluble materials. Depending upon the boiling point of the solvent used, TV-SPME allows for large sample volumes (e.g., up to hundreds of microliters). On-fiber derivatization may also be performed using TV-SPME. TV-SPME has been used to analyze drugs and their metabolites in hair, urine, and saliva. This simple technique has also been applied to street drugs, lipids, fuel samples, post-blast explosive residues, and pollutants in water. This paper highlights the use of TV-SPME to identify illegal adulterants in very small samples (microliter quantities) of alcoholic beverages. Both gamma-hydroxybutyrate (GHB) and gamma-butyrolactone (GBL) were identified at levels that would be found in spiked drinks. Derivatization by a trimethylsilyl agent allowed for conversion of the aqueous matrix and GHB into their TMS derivatives. Overall, TV-SPME is quick, easy, and requires no sample preparation aside from placing the sample into a headspace vial.

A GBL volume study was performed to demonstrate the sensitivity of TV-SPME compared to headspace and immersion SPME. A 100ppmv sample of GBL in water was prepared and placed into 20 mL headspace vials with volumes of 1, 3, 10, 30, 100, 300, 1000, 3000, and 10,000 &#181;L. The phase ratio of the samples allowed for TV-SPME (1-3 &#181;L), Headspace SPME (10 &#8211; 3,000 &#181;L) and Immersion SPME (10,000 &#181;L). All samples were analyzed in triplicate and the average peak area was plotted against the sample ...

Watch this Scientific Journal Video about Gas Chromatography-Mass Spectrometry Paired with Total Vaporization Solid-Phase Microextraction as a Forensic Tool at JoVE.com

Gas Chromatography-Mass Spectrometry Paired with Total Vaporization Solid-Phase Microextraction as a Forensic Tool

Total Vaporization Solid Phase Microextraction (TV-SPME) completely vaporizes a liquid sample whilst analytes are sorbed onto a SPME fiber. This allows for partitioning of the analyte between only the solvent vapor and the SPME fiber coating.

Gas Chromatography &#8211; Mass Spectrometry (GC-MS) is a frequently used technique for the analysis of numerous analytes of forensic interest, including ...

gas-chromatography-mass-spectrometry-paired-with-total-vaporization

Research

JoVE Journal

Chemistry

6.9K Views.  Indiana University - Purdue University Indianapolis. Total Vaporization Solid Phase Microextraction (TV-SPME) completely vaporizes a liquid sample whilst analytes are sorbed onto a SPME fiber. This allows for partitioning of the analyte between only the solvent vapor and the SPME fiber coating.

Video: Gas Chromatography-Mass Spectrometry Paired with Total Vaporization Solid-Phase Microextraction as a Forensic Tool

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.

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 ...

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 ...

Environment

Quantitative Analysis by Thermogravimetry-Mass Spectrum Analysis for Reactions with Evolved Gases

During energy conversion, material production, and metallurgy processes, reactions often have the features of unsteadiness, multistep, and multi-intermediates. Thermogravimetry-mass spectrum (TG-MS) is seen as a powerful tool to study reaction features. However, reaction details and reaction mechanics have not been effectively obtained directly from the ion current of TG-MS. Here, we provide a method of an equivalent characteristic spectrum analysis (ECSA) for analyzing the mass spectrum and giving the mass flow rate of reaction gases as precise as possible. The ECSA can effectively separate overlapping ion peaks and then eliminate the mass discrimination and temperature-dependent effect. Two example experiments are presented: (1) the decomposition of CaCO3 with evolved gas of CO2 and the decomposition of hydromagnesite with evolved gas of CO2 and H2O, to evaluate the ECSA on single-component system measurement and (2) the thermal pyrolysis of Zhundong coal with evolved gases of inorganic gases CO, H2, and CO2, and organic gases C2H4, C2H6, C3H8, C6H14, etc., to evaluate the ECSA on multi-component system measurement. Based on the successful calibration of the characteristic spectrum and relative sensitivity of specific gas and the ECSA on mass spectrum, we demonstrate that the ECSA accurately gives the mass flow rates of each evolved gas, including organic or inorganic gases, for not only single but multi-component reactions, which cannot be implemented by the traditional measurements.

Precise determination of the evolved gases&#39; flow rate is key to study the details of reactions. We provide a novel quantitative analysis method of equivalent characteristic spectrum analysis for thermogravimetry-mass spectrum analysis by establishing the calibration system of the characteristic spectrum and relative sensitivity, for obtaining the flow rate.

During energy conversion, material production, and metallurgy processes, reactions often have the features of unsteadiness, multistep, and ...

Engineering

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. ...

Profiling Volatile Compounds in Blackcurrant Fruit using Headspace Solid-Phase Microextraction Coupled to Gas Chromatography-Mass Spectrometry

There is an increasing interest in measuring volatile organic compounds (VOCs) emitted by ripe fruits for the purpose of breeding varieties or cultivars with enhanced organoleptic characteristics and thus, to increase consumer acceptance. High-throughput metabolomic platforms have been recently developed to quantify a wide range of metabolites in different plant tissues, including key compounds responsible for fruit taste and aroma quality (volatilomics). A method using headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) is described here for the identification and quantification of VOCs emitted by ripe blackcurrant fruits, a berry highly appreciated for its flavor and health benefits.
Ripe fruits of blackcurrant plants (Ribes nigrum) were harvested and directly frozen in liquid nitrogen. After tissue homogenization to produce a fine powder, samples were thawed and immediately mixed with sodium chloride solution. Following centrifugation, the supernatant was transferred into a headspace glass vial containing sodium chloride. VOCs were then extracted using a solid-phase microextraction (SPME) fiber and a gas chromatograph coupled to an ion trap mass spectrometer. Volatile quantification was performed on the resulting ion chromatograms by integrating peak area, using a specific m/z ion for each VOC. Correct VOC annotation was confirmed by comparing retention times and mass spectra of pure commercial standards run under the same conditions as the samples. More than 60 VOCs were identified in ripe blackcurrant fruits grown in contrasting European locations. Among the identified VOCs, key aroma compounds, such as terpenoids and C6 volatiles, can be used as biomarkers for blackcurrant fruit quality. In addition, advantages and disadvantages of the method are discussed, including prospective improvements. Furthermore, the use of controls for batch correction and minimization of drift intensity have been emphasized.

A headspace solid-phase microextraction-gas-chromatography platform is described here for fast, reliable, and semi-automated volatile identification and quantification in ripe blackcurrant fruits. This technique can be used to increase knowledge about fruit aroma and to select cultivars with enhanced flavor for the purpose of breeding.

There is an increasing interest in measuring volatile organic compounds (VOCs) emitted by ripe fruits for the purpose of breeding varieties or cultivars ...

Biochemistry

Capturing Actively Produced Microbial Volatile Organic Compounds from Human-Associated Samples with Vacuum-Assisted Sorbent Extraction

Volatile organic compounds (VOCs) from biological samples have unknown origins. VOCs may originate from the host or different organisms from within the host&#39;s microbial community. To disentangle the origin of microbial VOCs, volatile headspace analysis of bacterial mono- and co-cultures of Staphylococcus aureus, Pseudomonas aeruginosa, and Acinetobacter baumannii, and stable isotope probing in biological samples of feces, saliva, sewage, and sputum were performed. Mono- and co-cultures were used to identify volatile production from individual bacterial species or in combination with stable isotope probing to identify the active metabolism of microbes from the biological samples.
Vacuum-assisted sorbent extraction (VASE) was employed to extract the VOCs. VASE is an easy-to-use, commercialized, solvent-free headspace extraction method for semi-volatile and volatile compounds. The lack of solvents and the near-vacuum conditions used during extraction make developing a method relatively easy and fast when compared to other extraction options such as tert-butylation and solid phase microextraction. The workflow described here was used to identify specific volatile signatures from mono- and co-cultures. Furthermore, analysis of the stable isotope probing of human associated biological samples identified VOCs that were either commonly or uniquely produced. This paper presents the general workflow and experimental considerations of VASE in conjunction with stable isotope probing of live microbial cultures.

This protocol describes the extraction of volatile organic compounds from a biological sample with the vacuum-assisted sorbent extraction method, gas chromatography coupled with mass spectrometry using the Entech Sample Preparation Rail, and data analysis. It also describes culture of biological samples and stable isotope probing.

Volatile organic compounds (VOCs) from biological samples have unknown origins. VOCs may originate from the host or different organisms from within the ...

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 ...

Education

JoVE Science Education

Analytical Chemistry

Mass Spectrometry: Complex Analysis

Mass spectrometry is an important technique for the identification of pure compounds. However, it has some limitations for the analysis of complex mixtures, often due to excessive fragmentation making the spectrum too complicated to decipher. Mass spectrometry can be combined with suitable separation methods in sequence, forming hyphenated methods, which are useful in the analysis of complex mixtures.
GC&#8211;MS is a powerful hyphenated method commonly used in forensics and environmental laboratories for precise analysis of mixtures. Gas chromatography uses narrow capillary columns to separate components of a thermally stable volatile mixture and passes them to the mass spectrometer for analysis.
LC&#8211;MS is another hyphenated method that couples liquid chromatography with a mass spectrometer to analyze nonvolatile mixtures. To make liquid chromatography compatible with a mass spectrometer, suitable pressure-maintaining ionization interfaces or atmospheric-pressure ionization techniques like electrospray ionization, which is applicable for polar and ionic compounds, or atmospheric-pressure chemical ionization, which applies to less polar molecules, are used.
Another hybrid method, called tandem mass spectroscopy, uses multiple mass analyzers in sequence. Compared to other hyphenated methods, tandem spectroscopy is faster, more sensitive, and more selective due to smaller chemical noise. Tandem spectroscopy can be further combined with separation techniques to form GC&#8211;MS/MS or LC&#8211;MS/MS for more complex mixture analysis.
Capillary electrophoresis&#8211;mass spectrometry is a very sensitive technique commonly used to analyze large biomolecules like DNA, proteins, and polypeptides. This method feeds quadrupole mass analyzers with capillary effluents after passing through an electrospray ionization interface.

The analysis of complex mixtures requires the combination of separation methods and mass spectrometry in sequence, termed hyphenated methods.
GC&#8211;MS ...

JoVE Core

Unit 1

Principles of Mass Spectrometry

KEY TERMS AND CONCEPTS

Gas Chromatography: Introduction

Gas chromatography (GC) is a technique for separating and analyzing volatile compounds in a sample. Its primary purpose is to identify and quantify components in complex mixtures, making it essential in fields such as environmental analysis, pharmaceuticals, and petrochemicals. GC is also called vapor-phase chromatography (VPC) or gas-liquid partition chromatography (GLPC).
In GC,&#160; a sample is vaporized and mixed with an inert carrier gas (the mobile phase), which transports it through a column. The column is packed or coated with a stationary phase, either a liquid or solid material. Compounds in the sample are separated based on their boiling points, and compounds with lower boiling points elute first. The elution order- the sequence in which the compound exits the column- is visible on a chromatogram, where each peak corresponds to a specific compound.
There are two main types of gas chromatography:
1. Gas-liquid chromatography (GLC): In GLC, the stationary phase is a nonvolatile, thermally stable, chemically inert liquid, while the mobile phase is a carrier gas, typically helium. This technique is commonly used to separate compounds based on their boiling points.
&#160; 2. Gas-solid chromatography (GSC): GSC uses solid particulates like diatomaceous earth as the stationary phase and a carrier gas like helium as the mobile phase. GSC is primarily used for permanent gases and small polar molecules not retained by gas-liquid columns due to severe tailing of elution peaks.

Gas chromatography (GC) is a technique for separating and analyzing volatile compounds in a sample. Its primary purpose is to identify and quantify ...