JS is indebted to Prof. B. Hoge of the Inorganic Chemistry department, Bielefeld University, for the idea of establishing the presented inlet system. The analyzed phosphane was a generous gift from Prof. B. Hoge. Sample preparation of the analyzed compound was performed by M. Wiesemann. Photographs of the phospane were taken by Dr. J. Bader. The mechanical workshop of the faculty of chemistry is acknowledged for the manufacturing of the interface and the glass workshop of the faculty of chemistry for the manufacturing of the lockable test tubes with flanges. Prof. B. Hoge and Prof. H. Gr&#246;ger are acknowledged for funding of this publication.

1. Sample Preparation
<ol>
	<li>Use custom-made lockable test tubes with a flange (Figure 1) for transportation and transfer of the samples into the mass spectrometer. Prior to filling with sample, evacuate the lockable test tubes attached to a multiple manifold Schlenk line and remove residual water by heating with a heat gun. Vent the test tube with dry Argon and evacuate again, while heating.</li>
	<li>Immerse the lockable test tube into a cold trap filled with liquid nitrogen (CAUTION: Be careful when working with liquid nitrogen). Condense the sample into the test tube from a sample container attached to a manifold of the Schlenk line, close the lock on top of the test tube as well as the manifold and remove the locked test tube from the nitrogen bath. As mass spectrometry is very sensitive, a small amount is sufficient. Most of the analyte will remain in the lockable test tube during the analysis and is available for further experiments after the measurement.</li>
</ol>
<img alt="Figure 1" fo:content-width="5in" src="/files/ftp_upload/51858/51858fig1highres.jpg" width="500" /> 
Figure 1. Lockable test tube used for transfer of samples. A)&#160;Flange for attachment to the cold inlet system,&#160;(B) Teflon tap of the test tube to enable transport of a compound under air-free conditions, (C)&#160;screw to operate the Teflon tap.
2. Measurement of Mass Spectra
<ol>
	<li>Prior to sample measurement, tune and calibrate the mass spectrometer according to the instructions supplied by the manufacturer of your mass spectrometer (here, an Autospec X (Vacuum Generators, now Waters Corp., Manchester, UK) is used.&#160;Use perflourokerosene (PFK) as a standard&#160;and tune the mass spectrometer to a resolution of ca. 2,800 at m/z 119, 10% valley definition). Remove the push rod of the direct inlet from the ion source and install the outer interface for the test tube (Figure 2). To prevent heating of the push rod tip, set the inlet method to &#8220;septum&#8221; in the control software of the mass spectrometer.</li>
	<li>Connect the flange of the lockable test tube filled with the sample to the outer interface. Open the needle valve of the outer interface and evacuate the inlet. After evacuation, carefully open the ball valve to the ion source to complete the evacuation step. Close the needle valve of the outer interface. CAUTION: The Teflon tap of the test tube has to be closed in this step.</li>
	<li>Start a mass measurement in the software of the mass spectrometer. With closed needle valve, open the Teflon tap of the test tube very briefly, allowing gas phase molecules of the analyte to enter the outer part of the interface. Close the Teflon tap again. 
	NOTE: The outer part of the interface together with the space between the Teflon tap and the flange of the lockable test tube (compare Figures 1 and 2B) serves as an analyte gas reservoir during the analysis.</li>
	<li>Carefully open the needle valve while observing the vacuum gauge of the ion source. This step allows analyte molecules to enter the ion source of the mass spectrometer. The vacuum should not fall below 10-5 mbar during the measurement. 
	NOTE: Depending on the volatility of the analyte mass spectra of good quality are obtained at approximately 10-6 mbar. The mass spectrum of the sample is now recorded. Usually, the sample amount leaking into the instrument through the needle valve is sufficient to record mass spectra for several minutes. In case the intensity of the ions decreases, opening the needle valve a little more allows for more acquisition time. If the quality of the mass spectra recorded at 70 eV is not satisfying, mass spectra can be recorded using lower kinetic energies of the electrons, e.g., 20 eV.</li>
</ol>
<img alt="Figure 2" fo:content-width="5in" src="/files/ftp_upload/51858/51858fig2highres.jpg" width="500" /> 
Figure 2. Cold inlet system with empty lockable test tube fitted to the ion source of a VG Autospec X. A)&#160;Lockable test tube, (B)&#160;flange connection between test tube an cold inlet system, (C)&#160;needle valve, (D)&#160;stainless steel plate with seal as connection to the ion source, (E)&#160;interface of the direct inlet, the ceramic tip of the push rod is visible.
3. After the Measurement
<ol>
	<li>Close the needle valve of the outer interface. Close the ball valve to the ion source. Stop the acquisition of mass spectra in the software.</li>
	<li>Evacuate the inlet system while opening the needle valve completely. Vent the interface while ball valve and needle valve are closed. Evacuate the interface again, open the needle valve during this step in order to remove residual sample vapor in the interface. Repeat this step at least 3x.</li>
	<li>Remove the lockable test tube from the interface. Continue with next sample or remove the outer interface from the flange of the ion source and replace it with the push rod.</li>
</ol>

<ol><li>Field, F. H., Franklin, J. L. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aField%2C+FH+%22Electron+Impact+phenomena+and+the+Properties+of+Gaseous+Ions+Revised+Edition%22">Electron Impact phenomena and the Properties of Gaseous Ions Revised Edition</a>. , Academic Press. (1957).</li>
<li>Schaeffer, O. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((An+Improved+Mass+Spectrometer+Ion+Source%5BTitle%5D)+AND+%22Rev.+Sci.+Instrum%22%5BJournal%5D)">An Improved Mass Spectrometer Ion Source.</a> Rev. Sci. Instrum. 25, 660-662 (1954).</li>
<li>Yamashita, M., Fenn, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Electrospray+Ion+Source+-+Another+Variation+of+the+Free-Jet+Theme%5BTitle%5D)+AND+%22J.+Phys.+Chem%22%5BJournal%5D)">Electrospray Ion Source - Another Variation of the Free-Jet Theme.</a> J. Phys. Chem. 88, 4451-4459 (1984).</li>
<li>Lubben, A. T., McIndoe, J. S., Weller, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Coupling+an+electrospray+ionization+mass+spectrometer+with+a+glovebox%3A+A+straightforward%2C+powerful%2C+and+convenient+combination+for+analysis+of+air-sensitive+organometallics%5BTitle%5D)+AND+%22Organometallics%22%5BJournal%5D)">Coupling an electrospray ionization mass spectrometer with a glovebox: A straightforward, powerful, and convenient combination for analysis of air-sensitive organometallics.</a> Organometallics. 27, 3303-3306 (2008).</li>
<li>Cooper, G. J. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Structural+and+Compositional+Control+in+%7BM12%7D+Cobalt+and+Nickel+Coordination+Clusters+Detected+Magnetochemically+and+with+Cryospray+Mass+Spectrometry%5BTitle%5D)+AND+%22Angewandte+Chemie+International+Edition%22%5BJournal%5D)">Structural and Compositional Control in {M12} Cobalt and Nickel Coordination Clusters Detected Magnetochemically and with Cryospray Mass Spectrometry.</a> Angewandte Chemie International Edition. 46, 1340-1344 (2007).</li>
<li>Wang, W. S., Tseng, P. W., Chou, C. H., Shiea, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Detection+of+reactive+1%2C2%2C3-hexatriene-5-one+monomer+by+low-temperature+atmospheric+pressure+ionization+mass+spectrometry%5BTitle%5D)+AND+%22Rapid+Communications+in+Mass+Spectrometry%22%5BJournal%5D)">Detection of reactive 1,2,3-hexatriene-5-one monomer by low-temperature atmospheric pressure ionization mass spectrometry.</a> Rapid Communications in Mass Spectrometry. 12, 931-934 (1998).</li>
<li>Wang, C. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Detection+of+a+thermally+unstable+intermediate+in+the+Wittig+reaction+using+low-temperature+liquid+secondary+ion+and+atmospheric+pressure+ionization+mass+spectrometry%5BTitle%5D)+AND+%22Journal+of+the+American+Society+for+Mass+Spectrometry%22%5BJournal%5D)">Detection of a thermally unstable intermediate in the Wittig reaction using low-temperature liquid secondary ion and atmospheric pressure ionization mass spectrometry.</a> Journal of the American Society for Mass Spectrometry. 9, 1168-1174 (1998).</li>
<li>Eelman, M. D., Blacquiere, J. M., Moriarty, M. M., Fogg, D. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Shining+new+light+on+an+old+problem%3A+Retooling+MALDI+mass+spectrometry+for+organotransition-metal+catalysis%5BTitle%5D)+AND+%22Angewandte+Chemie-International+Edition%22%5BJournal%5D)">Shining new light on an old problem: Retooling MALDI mass spectrometry for organotransition-metal catalysis.</a> Angewandte Chemie-International Edition. 47, 303-306 (2008).</li>
<li>Linden, H. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Liquid+injection+field+desorption+ionization%3A+a+new+tool+for+soft+ionization+of+samples+including+air-sensitive+catalysts+and+non-polar+hydrocarbons%5BTitle%5D)+AND+%22Eur.+J.+Mass+Spectrom%22%5BJournal%5D)">Liquid injection field desorption ionization: a new tool for soft ionization of samples including air-sensitive catalysts and non-polar hydrocarbons.</a> Eur. J. Mass Spectrom. 10, 459-468 (2004).</li>
<li>Gross, J. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Liquid+injection+field+desorption%2Fionization+of+reactive+transition+metal+complexes%5BTitle%5D)+AND+%22Analytical+and+Bioanalytical+Chemistry%22%5BJournal%5D)">Liquid injection field desorption/ionization of reactive transition metal complexes.</a> Analytical and Bioanalytical Chemistry. 386, 52-58 (2006).</li>
<li>Peterson, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Mass+Spectrometer+All-Glass+Heated+Inlet%5BTitle%5D)+AND+%22Analytical+Chemistry%22%5BJournal%5D)">Mass Spectrometer All-Glass Heated Inlet.</a> Analytical Chemistry. 34, 1850-1851 (1962).</li>
<li>Stafford, C., Morgan, T. D., Brunfeldt, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+mass+spectrometer+all-glass+heated+inlet%5BTitle%5D)+AND+%22International+Journal+of+Mass+Spectrometry+and+Ion+Physics%22%5BJournal%5D)">A mass spectrometer all-glass heated inlet.</a> International Journal of Mass Spectrometry and Ion Physics. 1, 87-92 (1968).</li>
<li>Hayes, S. A., Berger, R. J. F., Mitzel, N. W., Bader, J., Hoge, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Chlorobis%28pentafluoroethyl%29phosphane%3A+Improved+Synthesis+and+Molecular+Structure+in+the+Gas+Phase%5BTitle%5D)+AND+%22Chemistry-a+European+Journal%22%5BJournal%5D)">Chlorobis(pentafluoroethyl)phosphane: Improved Synthesis and Molecular Structure in the Gas Phase.</a> Chemistry-a European Journal. 17, 3968-3976 (2011).</li>
<li>Zakharov, A. V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Functionalized+Bis%28pentafluoroethyl%29phosphanes%3A+Improved+Syntheses+and+Molecular+Structures+in+the+Gas+Phase%5BTitle%5D)+AND+%22European+Journal+of+Inorganic+Chemistry%22%5BJournal%5D)">Functionalized Bis(pentafluoroethyl)phosphanes: Improved Syntheses and Molecular Structures in the Gas Phase.</a> European Journal of Inorganic Chemistry. , 3392-3404 (2013).</li>
</ol>

The authors have nothing to disclose.

The acquisition of mass spectra from compounds which decompose under standard sample preparation procedures is presented in this protocol. The presented technique is designed for the analysis of metal organyls, silanes and phosphane, which are highly susceptible to oxidation and/or hydrolysis, making it interesting especially for inorganic chemists. In order to achieve optimal results, vacuum or air-free conditions have to be preserved throughout the analysis. Therefore the protocol should be followed meticulously. In ca...

The analysis of compounds, such as metal organyls, silanes, or phosphanes by mass spectrometry is not always feasible. Several of these compounds are known to decompose rapidly when in contact with air. Therefore the most crucial steps when measuring mass spectra are sample preparation, the transfer of the analyte into the mass spectrometer and ion generation in the absence of air. In this protocol, we describe a strategy to meet these requirements and present an inlet system, which makes it possible to obtain mass spectra of volatile compounds previously not to be analyzed by mass spectrometry due to their difficult handling and rapid decomposition under ambient conditions. Thereby, unambiguous identification of novel or existing volatile metal organyls, silanes and phosphanes, susceptible to oxidation or hydrolysis, can now be performed with the assistance of mass spectrometry. There are two requirements which have to be met in order to analyze compounds which are susceptible to oxidation or hydrolysis: sample preparation and ion generation under inert conditions. The last premise can be easily met using a mass spectrometer with an ion source operating under vacuum. This is the case with most matrix-assisted-laser-desorption/ionization (MALDI) mass spectrometers and with all electron impact ionization (EI) mass spectrometers1,2. Electrospray ionization (ESI) is not readily compatible for the analysis of compounds susceptible to oxidation or hydrolysis, as the ionization process takes place under ambient conditions3. However, for some compounds which react not vigorously with oxygen or water, the drying and nebulizing gas with which most ESI sources are operated is sufficient for analysis by mass spectrometry4. This is also the case for Ionization strategies similar to ESI, e.g., low-temperature ESI, low-temperature atmospheric pressure ionization, and low-temperature liquid secondary ion mass spectrometry5-7. In contrast, sample preparation and transfer into the ion source under inert conditions is much more challenging. Both MALDI and ESI instruments have been coupled with glove boxes in order to enable sample preparation of compounds susceptible to oxidation and/or hydrolysis in an inert atmosphere4,8. The mass spectrometer is interfaced to the glove box either with a transfer capillary (ESI) or directly attached to the glove box (MALDI). The coupling of a glove box to a mass spectrometer via a transfer capillary would also be possible using another ionization strategy &#8211; liquid injection field desorption/ionization (LIFDI) &#8211; with which the analysis of sensitive compounds was reported9,10.
Additionally, MALDI and LIFDI are not suitable for the analysis of highly volatile compounds. MALDI requires the co-crystallization of the analyte with a matrix and LIFDI requires the deposition of the analyte onto an emitter from a solution. With both ionization strategies it is very likely that the analyte will evaporate along with the solvent. In contrast to MALDI instruments, EI mass spectrometers usually offer several methods for introducing the sample into the ion source: the direct inlet probe (small amounts of solids, oils, or waxes are deposited into an aluminum crucible which is introduced using a push rod), a septum inlet (for liquids), or coupling with a gas chromatograph. Again, at least part of the sample transfer takes place under ambient conditions and is difficult to perform under an inert atmosphere.
In the 1960&#8217;s, a sample inlet system was presented which enables the introduction of samples under vacuum into the ion source of an EI instrument &#8211; the all-glass heated inlet system (AGHIS)11,12. Here, the sample was located inside a sealed piece of glass capillary, which was inserted into the AGHIS. Subsequently, the AGHIS was evacuated and the glass container with the sample was broken. The AGHIS was then heated to evaporate the sample which reached the ion source of an EI mass spectrometer by means of a leak. When the glass capillary with the sample was prepared inside a glove box, the sample could be introduced into the mass spectrometer without any contact to air. However, the AGHIS is an apparatus which is not commercially available and difficult to assemble even for a skilled glassblower workshop. Due to the large dimensions switching between direct inlet using a push rod and AGHIS is not straight forward.
In our mass spectrometry lab, we developed a similar inlet system in the style of the AGHIS. However, as it is not possible to heat the inlet system, the analyte has to exhibit a certain volatility in order to enter the ion source of the mass spectrometer. The volatility of the analyte has to be sufficient, to allow for the transfer of the compound under vacuum at liquid nitrogen temperature &#8211; either by boiling or sublimation. The custom-made inlet system consists of a stainless steel plate, which is positioned at the direct inlet system, a stainless steel tube with a needle valve, and a flange, to which a lockable test tube containing the sample can be attached. The installation of the cold inlet system requires no modifications to the mass spectrometer (Autospec X, Vacuum Generators, now Waters Corp., Manchester, UK) &#8211; switching between cold inlet system and direct inlet using a push rod can be performed easily within seconds.
The presented inlet system is of particular use when metal organyls, silanes, or phosphanes, susceptible to oxidation or hydrolysis, have to be analyzed. These compounds are commonly analyzed using nuclear magnetic resonance (NMR) spectroscopy or&#160;infrared (IR) spectroscopy. Unfortunately, these methods allow not always for an unambiguous identification of a compound because they yield incomplete information, e.g., when elements such as chlorine or bromine are part of the molecule. Gas electron diffraction on the other hand is able to provide detailed information about the analyte, however, the method is very time consuming, sample preparation is difficult, and only few groups are able to conduct these analysis13,14. Here, the cold inlet system for the analysis of metal organyls, silanes, or phosphanes, susceptible to oxidation or hydrolysis by EI mass spectrometry is of great use for (in)organic chemists enabling the unambiguous identification of novel compounds by supplying them with information regarding the mass of a molecule and of characteristic fragment ions. The only prerequisite for the measurement of mass spectra for a substance is a certain volatility at reduced pressure.

<table><tbody><tr><td>VG Autospec X</td><td>Micromass Co. UK Ltd (now Waters)</td><td></td><td>Other EI mass spectrometers with direct inlet using a push rod should also be compatible with this technique</td></tr><tr><td>Lockable test tubes with flange</td><td></td><td></td><td>Custom made, teflon tap should be used for locking the test tube</td></tr><tr><td>Interface for lockable test tubes</td><td></td><td></td><td>Custom made, interface is prepared from stainless steel. Needle valve has to be included into the interface-design!</td></tr><tr><td>Schlenk line</td><td></td><td></td><td>Custom made, has to include vacuum pump for evacuation of thest tubes and cold trap with liquid nitrogen for trapping of the sample</td></tr></tbody></table>

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.

An EI mass spectrum of tris(trifluoromethyl)phosphane is presented in Figure 3, a compound, which decomposes rapidly when in contact with air (Figure 4). The presented interface allows for the straight forward measurement of mass spectra for these compounds. The operation of the novel interface is easy and fast and presents no obstacle when operating the mass spectrometer with the routinely applied direct inlet using the push rod.
<p class="jove_content" fo:keep-together.within-page=...

Watch this Scientific Journal Video about Analysis of Volatile and Oxidation Sensitive Compounds Using a Cold Inlet System and Electron Impact Mass Spectrometry at JoVE.com

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 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 ...

analysis-volatile-oxidation-sensitive-compounds-using-cold-inlet

Research

JoVE Journal

Chemistry

9.6K Views.  Bielefeld University.  Deze video geeft een protocol voor de massaspectrometrische analyse van de vluchtige en oxidatie gevoelige verbindingen met elektronimpactionisatie ionisatie. De voorgestelde techniek is bijzonder interessant voor anorganische chemici werken met metaal organyls, silanen of fosfanen die moeten worden behandeld met inerte omstandigheden, zoals de Schlenk-techniek. 

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

Characterizing Bacterial Volatiles using Secondary Electrospray Ionization Mass Spectrometry (SESI-MS)

Secondary electrospray ionization mass spectrometry (SESI-MS) is a method developed for the rapid detection of volatile compounds, without the need for sample pretreatment. The method was first described by Fenn and colleagues1 and has been applied to the detection of illicit drugs2 and explosives3-4, the characterization of skin volatiles5, and the analysis of breath6-7.
SESI ionization occurs by proton transfer reactions between the electrospray solution and the volatile analyte, and is therefore suitable for the analysis of hetero-organic molecules, just as in traditional electrospray ionization (ESI). However, unlike standard ESI, the proton transfer process of SESI occurs in the vapor phase rather than in solution (Fig. 1), and therefore SESI is best suited for detecting organic volatiles and aerosols.
We are expanding the use of SESI-MS to the detection of bacterial volatiles as a method for bacterial identification and characterization8. We have demonstrated that SESI-MS volatile fingerprinting, combined with a statistical analysis method, can be used to differentiate bacterial genera, species, and mixed cultures in a variety of growth media.8 Here we provide the steps for obtaining bacterial volatile fingerprints using SESI-MS, including the instrumental parameters that should be optimized to ensure robust bacterial identification and characterization.

Characterizing Bacterial Volatiles using Secondary Electrospray Ionization Mass Spectrometry SESI-MS

Secondary electrospray ionization mass spectrometry (SESI-MS) enables the detection of volatile organic compounds (VOCs) without the need for any sample pretreatment. This protocol provides instructions for the rapid (within minutes) characterization of bacterial VOCs using SESI-MS.

Secondary electrospray ionization mass spectrometry (SESI-MS) is a method developed for the rapid detection of volatile compounds, without the need for ...

Bioengineering

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 ...

Extraction of Aqueous Metabolites from Cultured Adherent Cells for Metabolomic Analysis by Capillary Electrophoresis-Mass Spectrometry

Metabolomic analysis is a promising omics approach to not only understand the specific metabolic regulation in cancer cells compared to normal cells but also to identify biomarkers for early-stage cancer detection and prediction of chemotherapy response in cancer patients. Preparation of uniform samples for metabolomic analysis is a critical issue that remains to be addressed. Here, we present an easy and reliable protocol for extracting aqueous metabolites from cultured adherent cells for metabolomic analysis using capillary electrophoresis-mass spectrometry (CE-MS). Aqueous metabolites from cultured cells are analyzed by culturing and washing cells, treating cells with methanol, extracting metabolites, and removing proteins and macromolecules with spin columns for CE-MS analysis. Representative results using lung cancer cell lines treated with diamide, an oxidative reagent, illustrate the clearly observable metabolic shift of cells under oxidative stress. This article would be especially valuable to students and investigators involved in metabolomics research, who are new to harvesting metabolites from cell lines for analysis by CE-MS.

The purpose of this article is to describe a protocol for extraction of aqueous metabolites from cultured adherent cells for metabolomic analysis, particularly, capillary electrophoresis-mass spectrometry.

Metabolomic analysis is a promising omics approach to not only understand the specific metabolic regulation in cancer cells compared to normal cells but ...

Cancer Research

Fizzy Extraction of Volatile Organic Compounds Combined with Atmospheric Pressure Chemical Ionization Quadrupole Mass Spectrometry

Chemical analysis of volatile and semivolatile compounds dissolved in liquid samples can be challenging. The dissolved components need to be brought to the gas phase, and efficiently transferred to a detection system. Fizzy extraction takes advantage of the effervescence phenomenon. First, a carrier gas (here, carbon dioxide) is dissolved in the sample by applying overpressure and stirring the sample. Second, the sample chamber is decompressed abruptly. Decompression leads to the formation of numerous carrier gas bubbles in the sample liquid. These bubbles assist the release of the dissolved analyte species from the liquid to the gas phase. The released analytes are immediately transferred to the atmospheric pressure chemical ionization interface of a triple quadrupole mass spectrometer. The ionizable analyte species give rise to mass spectrometric signals in the time domain. Because the release of the analyte species occurs over short periods of time (a few seconds), the temporal signals have high amplitudes and high signal-to-noise ratios. The amplitudes and areas of the temporal peaks can then be correlated with concentrations of the analytes in the liquid samples subjected to fizzy extraction, which enables quantitative analysis. The advantages of fizzy extraction include: simplicity, speed, and limited use of chemicals (solvents).

Fizzy extraction is a new laboratory technique for analysis of volatile and semivolatile compounds. A carrier gas is dissolved in the liquid sample by applying overpressure and stirring the sample. The sample chamber is then decompressed. The analyte species are liberated to the gas phase due to effervescence.

Chemical analysis of volatile and semivolatile compounds dissolved in liquid samples can be challenging. The dissolved components need to be brought 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 ...

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

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

Versatile Dual-Inlet Sample Introduction System for Multi-Mode Single Particle Inductively Coupled Plasma Mass Spectrometry Analysis and Validation

Metal-containing nanoparticles (NP) can be characterized with inductively coupled plasma mass spectrometers (ICP-MS) in terms of their size and number concentration by using the single-particle mode of the instrument (spICP-MS). The accuracy of measurement depends on the setup, operational conditions of the instrument and specific parameters that are set by the user. The transport efficiency of the ICP-MS is crucial for the quantification of the NP and usually requires a reference material with homogenous size distribution and a known particle number concentration.
Currently, NP reference materials are available for only a few metals and in limited sizes. If particles are characterized without a reference standard, the results of both size and particle number may be biased. Therefore, a dual-inlet setup for characterizing nanoparticles with spICP-MS was developed to overcome this problem. This setup is based on a conventional introduction system consisting of a pneumatic nebulizer (PN) for nanoparticle solutions and a microdroplet generator (&#181;DG) for ionic calibration solutions. A new and flexible interface was developed to facilitate the coupling of &#181;DG, PN and the ICP-MS system. The interface consists of available laboratory components and allows for the calibration, nanoparticle (NP) characterization and cleaning of the arrangement, while the ICP-MS instrument is still running.
Three independent analysis modes are available for determining particle size and number concentration. Each mode is based on a different calibration principle. While mode I (counting) and mode III (&#181;DG) are known from the literature, mode II (sensitivity), is used to determine the transport efficiency by inorganic ionic standard solutions only. It is independent of NP reference materials. The &#181;DG based inlet system described here guarantees superior analyte sensitivities and, therefore, lower detection limits (LOD). The size dependent LODs achieved are less than 15 nm for all NP (Au, Ag, CeO2) investigated.

Here we provide a protocol for the use of a dual-inlet system for single particle inductively coupled mass spectrometry which allows for a standard independent nanoparticle characterization.

Metal-containing nanoparticles (NP) can be characterized with inductively coupled plasma mass spectrometers (ICP-MS) in terms of their size and number ...

Fruit Volatile Analysis Using an Electronic Nose

Numerous and diverse physiological changes occur during fruit ripening, including the development of a specific volatile blend that characterizes fruit aroma. Maturity at harvest is one of the key factors influencing the flavor quality of fruits and vegetables1. The validation of robust methods that rapidly assess fruit maturity and aroma quality would allow improved management of advanced breeding programs, production practices and postharvest handling. 
Over the last three decades, much research has been conducted to develop so-called electronic noses, which are devices able to rapidly detect odors and flavors2-4. Currently there are several commercially available electronic noses able to perform volatile analysis, based on different technologies. The electronic nose used in our work (zNose, EST, Newbury Park, CA, USA), consists of ultra-fast gas chromatography coupled with a surface acoustic wave sensor (UFGC-SAW). This technology has already been tested for its ability to monitor quality of various commodities, including detection of deterioration in apple5; ripeness and rot evaluation in mango6; aroma profiling of thymus species7; C6 volatile compounds in grape berries8; characterization of vegetable oil9 and detection of adulterants in virgin coconut oil10. 
This system can perform the three major steps of aroma analysis: headspace sampling, separation of volatile compounds, and detection. In about one minute, the output, a chromatogram, is produced and, after a purging cycle, the instrument is ready for further analysis. The results obtained with the zNose can be compared to those of other gas-chromatographic systems by calculation of Kovats Indices (KI). Once the instrument has been tuned with an alkane standard solution, the retention times are automatically converted into KIs. However, slight changes in temperature and flow rate are expected to occur over time, causing retention times to drift. Also, depending on the polarity of the column stationary phase, the reproducibility of KI calculations can vary by several index units11. A series of programs and graphical interfaces were therefore developed to compare calculated KIs among samples in a semi-automated fashion. These programs reduce the time required for chromatogram analysis of large data sets and minimize the potential for misinterpretation of the data when chromatograms are not perfectly aligned.
We present a method for rapid volatile compound analysis in fruit. Sample preparation, data acquisition and handling procedures are also discussed.

A rapid method for volatile compound analysis in fruit is described. The volatile compounds present in the headspace of a homogenate of the sample are rapidly separated and detected with ultra-fast gas chromatography (GC) coupled with a surface acoustic wave (SAW) sensor. A procedure for data handling and analysis is also discussed.

Numerous and diverse physiological changes occur during fruit ripening, including the development of a specific volatile blend that characterizes fruit ...

Biology

Introduction to Mass Spectrometry

Source: Laboratory of Dr. Khuloud Al-Jamal - King&#39;s College London

Mass spectrometry is an analytical chemistry technique that enables the identification of unknown compounds within a sample, the quantification of known materials, the determination of the structure, and chemical properties of different molecules.
A mass spectrometer is composed of an ionization source, an analyzer,&#160;and a detector. The process involves the ionization of chemical compounds to generate ions. When using inductively coupled plasma (ICP), samples containing elements of interest are introduced into argon plasma as aerosol droplets. The plasma dries the aerosol, dissociates the molecules, and then removes an electron from the components to be detected by the mass spectrometer. Other ionization methods such as electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) are used to analyze biological samples. Following the ionization procedure, ions are separated in the mass spectrometer according to their mass-to-charge ratio (m/z), and the relative abundance of each ion type is measured. Finally, the detector commonly consists in an electron multiplier where the collision of ions with a charged anode leads to a cascade of increasing number of electrons, which can be detected by an electrical circuit connected to a computer.
In this video, the procedure of ICP-MS analysis will be described by the detection of 56Fe as an example.

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

Samenvatting

Meer video's verkennen