Name: quantitative analysis by thermogravimetry-mass spectrum analysis for reactions with evolved gases
Uploaded: 2018-10-29T14:00:00.000+00:00
Duration: 6 min 51 s
Description: Watch this Scientific Journal Video about Quantitative Analysis by Thermogravimetry-Mass Spectrum Analysis for Reactions with Evolved Gases at JoVE.com

The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (Grant No. 51506199).

1. Calibration of ECSA for the TG-MS System
<ol>
	<li>Calibration of the characteristic spectrum
	<ol>
		<li>Prepare the evolved gases of CO2, H2O, CH4, He, etc. to be calibrated, modulating the gas pressure at 0.15 MPa.</li>
		<li>Connect the gas cylinder to the TG-MS system by stainless steel tube and purge the individual gas into the TG-MS system with a flow rate of 100 mL/min.</li>
		<li>Monitor the mass spectrum of the individual gas. Carefully watch and compare the characteristic peak of gases to be calibrated and the possible impurity gases in the mass spectrum by TG-MS to confirm the species and purity of the gases. 
		NOTE: The above-mentioned gases can be bought directly in gas cylinders or decomposed from some testing samples (except He). He is used as carrier gas in both the calibration and the test. 
		CAUTION: For some substances which are harmful to the TG or MS, the carrier gas must be used.</li>
	</ol>
	</li>
	<li>Calibration of the relative sensitivity
	<ol>
		<li>Purge the reference gas He with a flow rate of 300 mL/min into the TG-MS system for 20 min to clean the system.</li>
		<li>Purge synchronously one type of calibrated gas, such as CO2 or H2O, and the reference gas He into the TG-MS system with a flow rate of 100 mL/min.</li>
		<li>Calculate the relative sensitivity of each gas according to the known flow rate and the mass spectrum (Equation 1). 
		<img alt="Equation 1" src="/files/ftp_upload/58233/58233eq1.jpg" /> 
		Here, 
		<img alt="Equation 2" src="/files/ftp_upload/58233/58233eq2.jpg" /> = relative sensitivity of the k gas to the reference gas 
		<img alt="Equation 3" src="/files/ftp_upload/58233/58233eq3.jpg" /> = the given flow rate of the reference gas 
		<img alt="Equation 4" src="/files/ftp_upload/58233/58233eq4.jpg" /> = the given flow rate of the k gas 
		<img alt="Equation 5" src="/files/ftp_upload/58233/58233eq5.jpg" /> = the determined ion current for the k gas by MS, and 
		<img alt="Equation 6" src="/files/ftp_upload/58233/58233eq6.jpg" /> = the determined ion current for reference gas. 
		NOTE: The volumetric flow rates of the calibrated and reference gas must be known in advance.</li>
	</ol>
	</li>
</ol>
2. Testing Process of ECSA for the TG-MS System
<ol>
	<li>Preparation of the samples used for the test
	<ol>
		<li>Preparation of the samples of CaCO3 and hydromagnesite
		<ol>
			<li>Collect 10-g samples of CaCO3 with an average diameter of 15 &#181;m.</li>
			<li>Collect 10 g of a white block of hydromagnesite, break it into pieces of &#60; 3 mm in size, and grind the pieces with a machine-stirred mill to approximately 10 &#181;m.</li>
			<li>Dry all the samples for 24 h in the oven at a temperature of 105 &#176;C. 
			NOTE: The above steps can be implemented in parallel.</li>
		</ol>
		</li>
		<li>Preparation of the samples of Zhundong coals
		<ol>
			<li>Collect 20 g of Zhundong coal from the coalfield located at the Mori Kazak Autonomous County, Xinjiang province in China.</li>
			<li>To eliminate any external moisture, dry the coal in the oven at a temperature of 105 &#176;C for 24 h.</li>
			<li>Break and ground the coal in a mill to obtain a particle size range of 180 - 355 m.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Test of the thermal reactions
	<ol>
		<li>Purge the TG-MS system with the carrier gas He for 2 h to expel the air and moisture. Meanwhile, preheat the instrument to around 500 &#176;C and, then, cool it down to room temperature. 
		NOTE: The He gas was used as carrier gas for all the tests.</li>
		<li>Monitor the atmosphere by using MS in the first 20 min, carefully watching and comparing the characteristic peak of CO2, He, and the impurity gases of O2, N2, and H2O in the mass spectrum, to guarantee the lowest content of air and moisture, not affecting the experimental measurements.</li>
		<li>Weigh a sample of 10 mg by using the precision electronic balance and put the sample into an Al2O3 crucible.</li>
		<li>Put the Al2O3 crucible with the sample into the TG and close the furnace.</li>
		<li>Set the operating parameters. (1) For the CaCO3 test, start the temperature at 20 &#176;C and heat to 550 &#176;C with a heating rate of 10 K/min; then, for the modulating temperature program, heat to 800 &#176;C with alternating heating rates of 10 K/min and 20 K/min. (2) For the hydromagnesite and coal test, start the temperature at 20 &#176;C and use a heating rate of 10 K/min, a hold time of 15 min, a stopping temperature of 1,000 &#176;C, and a gas flow rate of 20 mL/min; keep an m/z range of 2 - 200 for mode EI and 10 - 410 for mode PI. 
		NOTE: Mode PI was used to identify the organic gases, mainly used for the test of Zhundong coal pyrolysis in this study.</li>
	</ol>
	</li>
</ol>
3. Qualitative and Quantitative Analysis
<ol>
	<li>Get the 3-D mass spectrum data recorded by the computer connected with the TG-MS instrument.</li>
	<li>Calculate the actual parameters, including the mass flow rate and the concentration of each evolved gas, by using the ECSA method, based on the determined calibrated characteristic peak (step 2.1) and the relative sensitivity (step 2.2).</li>
	<li>Analyze the thermal reaction according to the actual parameters9.</li>
</ol>

<ol>
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The authors have nothing to disclose.

This protocol could be easily modified to accommodate other measurements for studying evolved gases and pyrolysis reactions by a TG-MS system. As we know, the evolved volatile from the pyrolysis of biomass, coal, or other solid/liquid fuel does not always include only the inorganic gases (e.g., CO, H2, and CO2) but also the organic ones (e.g., C2H4, C6H5OH, and C7H8). Moreover, massive fragments would result from the organic gases, and secondary reactions would occur during pyrolysis11. Even though several conventional measurement methods, like the normal TG-MS coupling system, Fourier transform infrared (FTIR) spectrometry12, high-performance liquid chromatography (HPLC)13, and UV-vis absorption and fluorescence spectroscopies14, have been employed for the characterization of the volatile gases and tar, there are still some issues to be solved, including the minimization of the secondary reactions, the mitigation of recondensation of evolved volatile gases during measurement, and the reduction of excessive fragments. ECSA developed based on a TG-DTA-EI/PI-MS system can be used to investigate accurately the pyrolysis characteristics for real-time, in situ measurement. Because of the fundamentality, applicability, and generality of the ECSA, the quantitative analysis for massive volatile gases from pyrolysis can be easily implemented9.
It should be considered that ECSA based on the TG-MS system is a powerful tool to analyze the thermal reaction processes with evolved gases for not only the simple system but also for the complicated one. A key step to implement the ECSA method is to successfully build the calibration factor and the relative sensitivity of the required gases. It also should be noted that the testing conditions of MS must be the same (or very similar) as those for calibration. Specifically, the reference gas for calibrating the relative sensitivity must be the same as the reference gas for the testing process, and it must never react with the evolved gases. In this study, helium is chosen as the reference gas in order to analyze CO2 and H2O in the measurement. Further, we believe that the ECSA can be used to characterize the elementary reactions if the calibration factor and relative sensitivity of the reactants or products in the elementary reactions are successfully built. On the other hand, since the ECSA separates the mass spectrum of all evolved gases into the spectra of different components, the matrix constructed by the ion current of various evolved gases must be solved before the quantitative results are obtained. The matrix can be expected to be large, should there be a large quantity of evolved gas species. Therefore, matrix solution is also key to the implementation of ECSA.
Finally, ECSA has much more advantages than the traditional TG-MS analysis methods. The key one is that the ECSA can provide the exact quantitative information (i.e., the flow rate, the concentration, and the partial pressure) for all gases. Another advantage is that, since ECSA treats with the IC of mass spectrum from the point of coupling characteristics (i.e., the equal relative pressure between TG and MS), it radically eliminates the mass discrimination of MS and the temperature-dependent effect of TG. And further, the issue of time delay during the measurement of reactions with evolved gases (especially solid particle reactions) can also be effectively resolved by varying the flow rate of the carrier gas and the temperature of TG. However, due to the MS, the ECSA cannot be used to determine reactions without evolved gases, and there is still some difficulty in dealing with the elementary reactions. Since all reactions accompany a change of heat, we are developing a new method to correlate the heat change into the ECSA to provide quantitative information for reactions without evolved gases but with heat change.

Understanding in depth the real features of a reaction process is one critical issue for the development of advanced materials and the establishment of a new energy conversion system or metallurgy production process1. Almost all reactions are carried out under unsteady conditions, and because their parameters, including the concentration and flow rate of reactants and products, always change with the temperature or pressure, it is difficult to clearly characterize the reaction feature by only one parameter, for instance through the Arrhenius Equation. In fact, the concentration implies only the relationship between the component and the mixture. Real reaction behavior might not be affected, even though the concentration of a component in one complicated reaction is adjusted to a great extent since the other components might have a stronger influence on it. On the contrary, the flow rate of each component, as an absolute quantity, can give persuasive information to understand the characteristics of the reactions, especially very complicated ones.
At present, the TG-MS coupling system equipped with the electron ionization (EI) technique has been used as a prevalent tool for analyzing the features of reactions with evolved gases2,3,4. However, first, it should be noted that the ion current (IC) obtained from an MS system makes it difficult to directly reflect the flow rate or concentration of the evolved gas. The massive IC overlap, fragment, severe mass discrimination, and diffusion effect of gases in the furnace of a thermogravimeter can greatly hamper the quantitative analysis for TG-MS5. Second, EI is the most common and readily available strong ionization technique. An MS system equipped with EI easily results in fragments and does not often directly reflect some organic gases with a larger molecular weight. Therefore, MS systems with different soft ionization techniques (e.g., photoionization [PI]) are required simultaneously to be hyphenated to a thermobalance and applied to evolved gas analysis6. Third, the intensity of the IC at some mass-to-charge ratios (m/z) cannot be used to determine the dynamic characteristic of any reaction gas, because it is often affected by the other ICs for a complex reaction with multicomponent evolved gases. For example, the drop in the IC curve of a specific gas does not necessarily indicate a decrease in its flow rate or concentration; instead, maybe it is affected by the other gases in the complex system. Thus, it is important to take into account all gases&#39; ICs, certainly with a carrier gas and inert gas.
In fact, quantitative analysis based on mass spectrum greatly depends on the determination of the calibration factor and relative sensitivity of the TG-MS system. Maciejewski and Baiker7 investigated in a thermal analyzer-mass spectrometer (TA-MS) system, in which the TA is connected by a heated capillary to a quadrupole MS, the effect of experimental parameters, including the concentration of gases species, temperature, flow rate, and properties of the carrier gas, on the sensitivity of the mass spectrometric analysis. The evolved gases were calibrated by the decomposition of the solids via a well-known, stoichiometric reaction and injecting a certain amount of gas into the carrier gas stream with a constant rate. The experimental results show that there is a negative linear correlation of the MS signal intensity of evolved gas to that of the carrier gas flow rate, and the evolved gas MS intensity is not influenced by the temperature and the amount of analyzed gas. Further, based on the calibration method, Maciejewski et al.8 invented the pulse thermal analysis (PTA) method, which provides an opportunity to determine the flow rate by simultaneously monitoring the changes of the mass, enthalpy, and gas composition resulted from the reaction course. However, it is still hard to give persuasive information about the complicated reaction (e.g., coal combustion/gasification) by using the traditional TG-MS analysis or PTA methods.
In order to overcome the difficulties and disadvantages of the traditional measuring and analysis method for the TG-MS system, we developed the quantitative analysis method of ECSA9. The fundamental principle of ECSA is based on the TG-MS coupling mechanism. The ECSA can take into account all gases&#39; ICs, including the reaction gases&#39;, carrier gases&#39;, and inert gases&#39;. After building the calibration factor and relative sensitivity of some gas, the real mass or molar flow rate of each component can be determined by the calculation of the IC matrix (i.e., the mass spectrum of TG-MS). Compared with the other methods, ECSA for the TG-MS system can effectively separate the overlapping spectrum and eliminate the mass discrimination and the temperature-dependent effect of TG. The data produced by ECSA have proved to be reliable via a comparison between the mass flow rate of evolved gas and mass loss data by differential thermogravimetry (DTG). In this study, we used an advanced TG-DTA-EI/PI-MS instrument10 to carry out the experiments (Figure 1). This instrument consists of a cylindrical quadrupole MS and a horizontal thermogravimetry-differential thermal analyzer (TG-DTA) equipped with both EI and PI mode, and with a skimmer interface. ECSA for the TG-MS system determines the physics parameters of all evolved gases by utilizing the actual TG-MS coupling mechanism (i.e., an equal relative pressure) to implement the quantitative analysis. The overall analysis process includes a calibration, the test itself, and data analysis (Figure 2). We present two example experiments: (1) the decomposition of CaCO3 with only evolved gas of CO2 and the decomposition of hydromagnesite with evolved gas of CO2 and H2O, to evaluate the ECSA on a single-component system measurement and (2) the thermal pyrolysis of brown coal with evolved gases of inorganic gases CO, H2, and CO2, and organic gases CH4, C2H4, C2H6, C3H8, C6H14, etc., to evaluate the ECSA on a multi-component system measurement. ECSA based on the TG-MS system is a comprehensive solution method for quantitatively determining the amount of evolved gas in thermal reactions.

<table><tbody><tr><td>CaCO&lt;sub&gt;3&lt;/sub&gt; and Ca(OH)&lt;sub&gt;2&lt;/sub&gt;</td><td>Sinopharm Chemical Reagent</td><td></td><td></td></tr><tr><td>hydromagnesite</td><td>Bangko Coarea in Tibet</td><td></td><td></td></tr><tr><td>Zhundong coal</td><td>the coal field in the Mori Kazak Autonomous County, Junggar basin, Xinjiang province of China</td><td></td><td></td></tr><tr><td>ThermoMass Photo/H</td><td>Rigaku Corporation</td><td></td><td></td></tr><tr><td>The STA449F3 synchronous thermal analyzer and QMS403C quadrupole MS analyzer</td><td>NETZSCH</td><td></td><td></td></tr></tbody></table>

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.

The thermal decomposition of CaCO3 is a relatively simple reaction, which was used to demonstrate the applicability of the ECSA method. After calibrating the characteristic peak and relative sensitivity of CO2 to carrier gas He, the actual mass flow rate of CO2 evolved by the thermal decomposition of CaCO3 was calculated by the ECSA method and was compared with the actual mass loss (Figure 3). It is shown that there is a good agreement between the mass flow rate of CO2 calculated by ECSA and the mass loss data by DTG during the entire measurement process. The relative error of mass flow rate of evolved gas to that of DTG is significantly lower, as shown by the blue and yellow lines in Figure 4. Also, the thermal decomposition process of hydromagnesite was analyzed by ECSA and the calibration data of CO2 and H2O (Figure 4). The carrier gas flow rate was chosen as 100 mL/min and the heating rate was set at 5, 10, 15, and 20 K/min. The calculated results were also in good agreement with the experimental TG/DTG data.
To further demonstrate the qualitative analysis of organic gases and the ability of ECSA to quantitatively determine the flow rate of a complicated reaction system, pyrolysis of Zhundong coal was carried out10. Combining both the PI and EI measuring modes, 16 types of volatile gases, including H2, CH4, H2O, CO, CO2, C2H4 (ethene), C3H6 (propene), C4H8 (butylene), C5H10 (pentene), C6H10 (hexadiene), C7H8 (toluene), C6H6O (phenol), C8H10 (ethylbenzene), C7H8O (anisole), C9H12 (propyl benzene), and C10H14 (butylbenzene), were clearly identified (Figure 5). After a detailed determination of mass spectrum and sensitivity of each gas to the carrier gas, the mass flow rate of each gas can be calculated. Straightforwardly, the ion current from the mass spectrum can be used to compare based on the same operating parameters (Figure 6).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/58233/58233fig1.jpg" /> 
Figure 1: Schematic diagram of the TG-DTA-EI/PI-MS system equipped with the EI and PI devices and skimmer-type interface. This TG-DTA-EI/PI-MS system mainly consists of a cylindrical quadrupole MS and a horizontal thermogravimetry-differential thermal analyzer (TG-DTA) equipped both the EI and PI devices. The MS and TG-DTA are connected by the skimmer interface. This figure has been modified from Li et al.10. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58233/58233fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/58233/58233fig2.jpg" /> 
Figure 2: Process diagram of ECSA for testing the thermal reactions. The overall analysis process can be divided into three parts that are calibration, test, and data analysis. The calibration part first provides the information of the characteristic spectrum and relative sensitivity of each gas in the reaction; this information is used for the subsequent calculation of the physics parameters, such as the flow rate, following the test. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58233/58233fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/58233/58233fig3.jpg" /> 
Figure 3: Comparison of the mass flow rate of evolved gas with the mass loss of DTG for the thermal decomposition of CaCO3. A comparison in mass loss between ECSA calculation results and measurement results from DTG was used to validate the reliability of the ECSA method. It is shown that there is a good agreement between the calculation by the ECSA and the measurements by DTG, and the relative error of mass flow rate of CO2 to that of DTG is significantly lower. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58233/58233fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/58233/58233fig4.jpg" /> 
Figure 4: Thermal decomposition process of hydromagnesite. These panels show (a) a 3-D mass spectrum graph plotted against temperature and m/z, (b) mass flow rates of CO2 calculated by ECSA at a heating rate of 5, 10, 15, and 20 K/min, (c) mass flow rates of H2O calculated by ECSA at a heating rate of 5, 10, 15, and 20 K/min, and (d) a comparison between ECSA-based flow rates and experimental TG/DTG data. Here, the carrier gas flow rate was chosen as 100 mL/min. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58233/58233fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/58233/58233fig5.jpg" /> 
Figure 5: 3-D mass spectrum graph of raw coal with the temperature and m/z in modes of EI and PI. (a) The EI mode was mainly used to identify inorganic gases such as CO2 and H2O, while (b) the PI mode was mainly done to identify organic gases such as C6H6 and C7H8. A joint use of EI and PI provides a comprehensive information for the pyrolysis of coal. This figure has been modified from Li et al.10. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58233/58233fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/58233/58233fig6.jpg" /> 
Figure 6: Mass ion curves of CH4 and C6H6O evolved from the raw coal sample and the pretreated Zhundong coal samples. One kind of inorganic gas, (a) CH4, and one organic gas, (b) C6H6O, were chosen to be represented in mass ion curves, for interpreting the function of ECSA on a quantitative analysis of the pyrolysis characteristics of different pretreated coals. Here the pretreated method includes the H2O-washed coal and HCl-washed coal. This figure has been modified from Li et al.10. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58233/58233fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Quantitative Analysis by Thermogravimetry-Mass Spectrum Analysis for Reactions with Evolved Gases at JoVE.com

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

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 ...

quantitative-analysis-thermogravimetry-mass-spectrum-analysis-for

Nanyang Technological University

Research

JoVE Journal

Engineering

9.3K Views.  University of Science and Technology Beijing. Deze methode kan helpen bij het beantwoorden van belangrijke vragen in de energie, chemie en het metallurgieveld over het identificeren van kinetische reactieparameters en geëvolueerde gassamenstellingen. Voor mij is een voordeel van deze techniek dat de massavloeistof van individuele gassen die uit reacties is voortgekomen kwalitatief en kwantitatief nauwkeurig kan worden bepaald. Door middel van deze methode, kan inzicht geven in reacties in de energie, chemie, metallurgie systeem, en ga z...

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

Analysis of Volatile and Oxidation Sensitive Compounds Using a Cold Inlet System and Electron Impact Mass Spectrometry

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The analysis of volatile and oxidation sensitive compounds by mass spectrometry is not easily achieved, as all state-of-the-art mass spectrometric methods require at least one sample preparation step, e.g., dissolution and dilution of the analyte (electrospray ionization), co-crystallization of the analyte with a matrix compound (matrix-assisted laser desorption/ionization), or transfer of the prepared samples into the ionization source of the mass spectrometer, to be conducted under atmospheric conditions. Here, the use of a sample inlet system is described which enables the analysis of volatile metal organyls, silanes, and phosphanes using a sector field mass spectrometer equipped with an electron impact ionization source. All sample preparation steps and the sample introduction into the ion source of the mass spectrometer take place either under air-free conditions or under vacuum, enabling the analysis of compounds highly susceptible to oxidation. The presented technique is especially of interest for inorganic chemists, working with metal organyls, silanes, or phosphanes, which have to be handled using inert conditions, such as the Schlenk technique. The principle of operation is presented in this video.

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The presented technique is especially of interest for inorganic chemists, working with metal organyls, silanes, or phosphanes which have to be handled using inert conditions, such as the Schlenk technique.

This video presents a protocol for the mass spectrometrical analysis of volatile and oxidation sensitive compounds using electron impact ionization. The ...

Chemistry

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 ...

PTR-ToF-MS Coupled with an Automated Sampling System and Tailored Data Analysis for Food Studies: Bioprocess Monitoring, Screening and Nose-space Analysis

Proton Transfer Reaction (PTR), combined with a Time-of-Flight (ToF) Mass Spectrometer (MS) is an analytical approach based on chemical ionization that belongs to the Direct-Injection Mass Spectrometric (DIMS) technologies. These techniques allow the rapid determination of volatile organic compounds (VOCs), assuring high sensitivity and accuracy. In general, PTR-MS requires neither sample preparation nor sample destruction, allowing real time and non-invasive analysis of samples. PTR-MS are exploited in many fields, from environmental and atmospheric chemistry to medical and biological sciences. More recently, we developed a methodology based on coupling PTR-ToF-MS with an automated sampler and tailored data analysis tools, to increase the degree of automation and, consequently, to enhance the potential of the technique. This approach allowed us to monitor bioprocesses (e.g. enzymatic oxidation, alcoholic fermentation), to screen large sample sets (e.g. different origins, entire germoplasms) and to analyze several experimental modes (e.g. different concentrations of a given ingredient, different intensities of a specific technological parameter) in terms of VOC content. Here, we report the experimental protocols exemplifying different possible applications of our methodology: i.e. the detection of VOCs released during lactic acid fermentation of yogurt (on-line bioprocess monitoring), the monitoring of VOCs associated with different apple cultivars (large-scale screening), and the in vivo study of retronasal VOC release during coffee drinking (nosespace analysis).

Proton Transfer Reaction Time of Flight Mass Spectrometry allows high-sensitivity, rapid and non-invasive analysis of volatile organic compounds. To demonstrate its potential, we give three examples: lactic acid fermentation of yogurt (on-line bioprocess monitoring), different apple genotypes (large-scale screening), and retronasal space after drinking coffee (nosespace analysis).

Proton Transfer Reaction (PTR), combined with a Time-of-Flight (ToF) Mass Spectrometer (MS) is an analytical approach based on chemical ionization that ...

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 ...

Quantitative Analysis of Vacuum Induction Melting by Laser-induced Breakdown Spectroscopy

Vacuum induction melting is a popular method for refining high purity metal and alloys. Traditionally, standard process control in metallurgy involves several steps, include drawing samples, cooling, cutting, transport to the laboratory, and analysis. The whole analysis process requires more than 30 minutes, which hinders on-line process control. Laser-induced breakdown spectroscopy is an excellent on-line analysis method that can satisfy the requirements of vacuum induction melting because it is fast and noncontact and does not require sample preparation. The experimental facility uses a lamp-pumped Q-switched laser to ablate melted liquid steel with an output energy of 80 mJ, a frequency of 5 Hz, a FWHM pulse width of 20 ns, and a working wavelength of 1,064 nm. A multi-channel linear charge coupled device (CCD) spectrometer is used to measure the emission spectrum in real time, with a spectral range from 190 to 600 nm and a resolution of 0.06 nm at a wavelength of 200 nm. The protocol includes several steps: standard alloy sample preparation and an ingredient test, smelting of standard samples and determination of the laser breakdown spectrum, and construction of the elements concentration quantitative analysis curve of each element. To realize the concentration analysis of unknown samples, the spectrum of a sample also needs to be measured and disposed with the same process. The composition of all main elements in the melted alloy can be quantitatively analyzed with an internal standard method. The calibration curve shows that the limit of detection of most metal elements ranges from 20-250 ppm. The concentration of elements, such as Ti, Mo, Nb, V, and Cu, can be lower than 100 ppm, and the concentrations of Cr, Al, Co, Fe, Mn, C, and Si range from 100-200 ppm. The R2 of some calibration curves can exceed 0.94.

During vacuum induction melting, laser-induced breakdown spectroscopy is used to perform real-time quantitative analysis of the main-ingredient elements of a molten alloy.

Vacuum induction melting is a popular method for refining high purity metal and alloys. Traditionally, standard process control in metallurgy involves ...

Derivatization and Separation of Barley Flour Metabolites into Four Fractions

Metabolomic Analysis of Barley by Gas Chromatography/Mass Spectrometry

Climate change increases drought risk to agriculture and impacts both food nutrient content and overall food security. Metabolomics is one way to observe and quantify the impacts of drought on grain and other agricultural products. The identified metabolites may allow for the identification of the biochemical response that allows the plant to tolerate stressful environments. The methodology presented herein allowed for the total metabolomic analysis of barley flour using gas chromatography/mass spectrometry (GC/MS). 
Barley flour metabolite extracts were fractionated into four fractions based on polarity. To allow for analysis by GC/MS, metabolites were derivatized to increase volatility and metabolite separation: fatty acids esters were derivatized into fatty acid methyl esters; sugars were oximated into their straight chain form; and metabolites with hydroxyl groups were converted to their corresponding silyl ethers. The derivatized samples were injected into the GC/MS and the generated mass spectra were used for metabolite identification by comparing the generated spectra to the National Institute of Standards and Technology (NIST) Tandem Mass Spectra library. The method described here can also be used to examine the total metabolome for other plants, furthering our understanding of the biochemical responses of stressed plants.

A method for metabolomic analysis of barley is presented. The method entails fractionation and derivatization of metabolites and analysis thereof by gas chromatography/mass spectrometry (GC/MS). Metabolomic analysis can be used to determine the effect of intercropping and drought stress on the grain.

Climate change increases drought risk to agriculture and impacts both food nutrient content and overall food security. Metabolomics is one way to observe ...

Environment

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

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.

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 ...

Identification and Quantification of Decomposition Mechanisms in Lithium-Ion Batteries; Input to Heat Flow Simulation for Modeling Thermal Runaway

The risks and possible accidents related to the normal use of lithium-ion batteries remain a serious concern. In order to get a better understanding of thermal runaway (TR), the exothermic decomposition reactions in anode and cathode were studied, using a Simultaneous Thermal Analysis (STA)/Gas Chromatography-Mass Spectrometry (GC-MS)/Fourier Transform Infrared (FTIR) spectrometer system. These techniques allowed the identification of the reaction mechanisms in each electrode, owing to the analysis of evolved gaseous species, the amount of heat released and mass loss. These results provided insight into the thermal events happening within a broader temperature range than covered in previously published models. This allowed the formulation of an improved thermal model to depict TR. The heat of reaction, activation energy, and frequency factor (thermal triplets) for each major exothermic process at material level were investigated in a Lithium Nickel-Manganese-Cobalt-Oxide (NMC (111))-Graphite battery cell. The results were analyzed, and their kinetics were derived. These data can be used to successfully simulate the experimental heat flow.

This work aims at determining the reaction kinetics of Li-ion battery cathode and anode materials undergoing thermal runaway (TR). Simultaneous Thermal Analysis (STA)/Fourier Transform Infrared (FTIR) spectrometer/Gas Chromatography Mass Spectrometry (GC-MS) were used to reveal thermal events and to detect evolved gases.

The risks and possible accidents related to the normal use of lithium-ion batteries remain a serious concern. In order to get a better understanding of ...

Unveiling Tea Aroma Complexity with Solvent-Assisted Flavor Evaporation Method

Tea Aroma Analysis Based on Solvent-Assisted Flavor Evaporation Enrichment

Tea aroma is an important factor in tea quality, but it is challenging to analyze due to the complexity, low concentration, diversity, and lability of the volatile components of tea extract. This study presents a method for obtaining and analyzing the volatile components of tea extract with odor preservation using solvent-assisted flavor evaporation (SAFE) and solvent extraction followed by gas chromatography-mass spectrometry (GC-MS). SAFE is a high-vacuum distillation technique that can isolate volatile compounds from complex food matrices without any non-volatile interference. A complete step-by-step procedure for tea aroma analysis is presented in this article, including the tea infusion preparation, solvent extraction, SAFE distillation, extract concentration, and analysis by GC-MS. This procedure was applied to two tea samples (green tea and black tea), and qualitative as well as quantitative results on the volatile composition of the tea samples were obtained. This method can not only be used for the aroma analysis of various types of tea samples but also for molecular sensory studies on them.

Author Spotlight: Exploring Tea Aroma Using Solvent-Assisted Flavor Evaporation Technique 

Presented here is a method for enriching and analyzing the volatile components of tea extracts using solvent-assisted flavor evaporation and solvent extraction followed by gas chromatography-mass spectrometry, which can be applied to all types of tea samples.

Tea aroma is an important factor in tea quality, but it is challenging to analyze due to the complexity, low concentration, diversity, and lability of the ...

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

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