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Aviv Amirav - One of the best experts on this subject based on the ideXlab platform.
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gc ms with photoionization of cold molecules in supersonic Molecular Beams approaching the softest ionization method
Journal of Mass Spectrometry, 2020Co-Authors: Alexander B Fialkov, Elias Ikonen, Tiina Laaksonen, Aviv AmiravAbstract:A new type of photoionization ion source was developed for the ionization of cold molecules in supersonic Molecular Beams (named Cold PI). The system was based on a GC-MS with supersonic Molecular Beams and its fly-through EI of cold molecules ion source (Cold EI) plus quadrupole mass analyzer. A continuously operated deuterium VUV photoionization lamp was added and placed above and between the supersonic nozzle and skimmer whereas the Cold EI ion source served only as a portion of the ion transfer ion optics. The supersonic nozzle and skimmer were voltage biased and the VUV light crossed the supersonic expansion about 10 mm from the nozzle. We obtained over three orders of magnitude enhancement in the relative abundance of the Molecular ion of squalane in Cold PI versus in photoionization of this compound as a thermal compound. Accordingly, we also proved that standard photoionization is not as soft ionization method as previously perceived for large compounds. We found that Cold PI is as soft as and possibly softer than field ionization; thus, it could be the softest known ionization method. The ionization yield was about 200-300 times weaker than with Cold EI yet our limit of detection was about 200 femtogram in SIM mode for cholesterol and pyrene which is reasonable. Practically, all hydrocarbons gave only Molecular ions with rather uniform response whereas alcohols gave some Molecular ions plus major fragment ions particularly with a loss of water (similarly to field ionization). We tested Cold PI in the GC-MS analysis of diesel fuels and analyzed the time averaged data for group type information. We also found that we can analyze the diesel fuels by fast under 20-s flow injection analysis in which the generated averaged mass spectrum of Molecular ions only could serve for the characterization of fuels.
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the pre separation of oxygen containing compounds in oxidised heavy paraffinic fractions and their identification by gc ms with supersonic Molecular Beams
Journal of Mass Spectrometry, 2019Co-Authors: H Potgieter, Piet De Coning, Riaan Bekker, Egmont Richard Rohwer, Aviv AmiravAbstract:The heavy petroleum fractions produced during refining processes need to be upgraded to useable products to increase their value. Hydrogenated heavy paraffinic fractions can be oxidised to produce high value products that contain a variety of oxygenates. These heavy oxygenated paraffinic fractions need to be characterised to enable the control of oxidation processes and to understand product properties. The accurate identification of the oxygenates present in these fractions by electron ionisation (EI) mass spectrometry is challenging due to the complexity of these heavy fractions. Adding to this challenge is the limited applicability of EI mass spectral libraries due to the absence of Molecular ions from the EI mass spectra of many oxygenates. The separation of oxygenates from the complex hydrocarbon matrix prior to high temperature GC-MS (HT-GC-MS) analysis reduces the complexity of these fractions and assists in the accurate identification of these oxygenates. Solid phase extraction (SPE) and supercritical fluid chromatography (SFC) were employed as prefractionation techniques. GC-MS with supersonic Molecular Beams (SMBs) (also named GC-MS with cold-EI) utilises a SMB interface with which EI is done with vibrationally cold sample compounds in a fly-through ion source (cold-EI) resulting in a substantial increase in the Molecular ion signal intensity in the mass spectrum. This greatly enhances the accurate identification of the oxygenates in these fractions. This study investigated the ionisation behaviour of oxygenated compounds using cold-EI. The prefractionation by SPE and SFC and the subsequent analysis with GC-MS with cold-EI were applied to an oxygenated heavy paraffinic fraction.
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electron ionization lc ms with supersonic Molecular Beams the new concept benefits and applications
Journal of Mass Spectrometry, 2015Co-Authors: Boaz Seemann, Alexander B Fialkov, Tal Alon, Svetlana Tsizin, Aviv AmiravAbstract:A new type of electron ionization LC-MS with supersonic Molecular Beams (EI-LC-MS with SMB) is described. This system and its operational methods are based on pneumatic spray formation of the LC liquid flow in a heated spray vaporization chamber, full sample thermal vaporization and subsequent electron ionization of vibrationally cold molecules in supersonic Molecular Beams. The vaporized sample compounds are transferred into a supersonic nozzle via a flow restrictor capillary. Consequently, while the pneumatic spray is formed and vaporized at above atmospheric pressure the supersonic nozzle backing pressure is about 0.15 Bar for the formation of supersonic Molecular Beams with vibrationally cold sample molecules without cluster formation with the solvent vapor. The sample compounds are ionized in a fly-though EI ion source as vibrationally cold molecules in the SMB, resulting in 'Cold EI' (EI of vibrationally cold molecules) mass spectra that exhibit the standard EI fragments combined with enhanced Molecular ions. We evaluated the EI-LC-MS with SMB system and demonstrated its effectiveness in NIST library sample identification which is complemented with the availability of enhanced Molecular ions. The EI-LC-MS with SMB system is characterized by linear response of five orders of magnitude and uniform compound independent response including for non-polar compounds. This feature improves sample quantitation that can be approximated without compound specific calibration. Cold EI, like EI, is free from ion suppression and/or enhancement effects (that plague ESI and/or APCI) which facilitate faster LC separation because full separation is not essential. The absence of ion suppression effects enables the exploration of fast flow injection MS-MS as an alternative to lengthy LC-MS analysis. These features are demonstrated in a few examples, and the analysis of the main ingredients of Cannabis on a few Cannabis flower extracts is demonstrated. Finally, the advantages of EI-LC-MS with SMB are listed and discussed.
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Measurement and optimization of organic chemical reaction yields by GC–MS with supersonic Molecular Beams
Tetrahedron, 2012Co-Authors: Aviv Amirav, Alexander Gordin, Boaz Seemann, Youlia Hagooly, Shlomo Rozen, Bogdan Belgorodsky, Hanit Marom, Michael Gozin, Alexander B FialkovAbstract:Abstract A new type of gas chromatograph mass spectrometer (GC–MS) was used for semi-online monitoring of organic chemical reactions for their yield optimization, mechanism elucidation, and for obtaining information on the reaction products identity and purity. It was used with reaction mixtures without prior separation and purification as needed for NMR, thereby saving time and effort. Our unique GC–MS named 5975-SMB Supersonic GC–MS is based on GC interface with the MS with supersonic Molecular Beams (SMB) and on ionization of the sample molecules during their axial flight through an open electron ionization ion source as vibrationally cold molecules. GC–MS with SMB is demonstrated to significantly extend the range of compounds amenable for analysis, practically always giving Molecular ions, enabling effective fast GC–MS analysis, and providing elemental formulas via isotope abundance analysis with unit mass resolution quadrupole MS. In addition, it uniquely provides uniform response to all compounds, a feature, which is vital for the measurement of chemical reaction yields. In this manuscript, four different organic synthetic reactions were studied and are described. Based on the collected data, we were able to better understand how the reaction conditions should be optimized in order to maximize the yields and purity of target products. Consequently, we propose that GC–MS with SMB can serve as a novel tool for the fast optimization of chemical reactions.
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a low thermal mass fast gas chromatograph and its implementation in fast gas chromatography mass spectrometry with supersonic Molecular Beams
Journal of Chromatography A, 2011Co-Authors: Alexander B Fialkov, Mati Morag, Aviv AmiravAbstract:Abstract A new type of low thermal mass (LTM) fast gas chromatograph (GC) was designed and operated in combination with gas chromatography mass spectrometry (GC–MS) with supersonic Molecular Beams (SMB), including GC–MS–MS with SMB, thereby providing a novel combination with unique capabilities. The LTM fast GC is based on a short capillary column inserted inside a stainless steel tube that is resistively heated. It is located and mounted outside the standard GC oven on its available top detector port, while the capillary column is connected as usual to the standard GC injector and supersonic Molecular beam interface transfer line. This new type of fast GC–MS with SMB enables less than 1 min full range temperature programming and cooling down analysis cycle time. The operation of the fast GC–MS with SMB was explored and 1 min full analysis cycle time of a mixture of 16 hydrocarbons in the C10H22 up to C44H90 range was achieved. The use of 35 mL/min high column flow rate enabled the elution of C44H90 in less than 45 s while the SMB interface enabled splitless acceptance of this high flow rate and the provision of dominant Molecular ions. A novel compound 9-benzylazidanthracene was analyzed for its purity and a synthetic chemistry process was monitored for the optimization of the chemical reaction yield. Biodiesel was analyzed in jet fuel (by both GC–MS and GC–MS–MS) in under 1 min as 5 ppm fatty acid methyl esters. Authentic iprodion and cypermethrin pesticides were analyzed in grapes extract in both full scan mode and fast GC–MS–MS mode in under 1 min cycle time and explosive mixture including TATP, TNT and RDX was analyzed in under 1 min combined with exhibiting dominant Molecular ion for TATP. Fast GC–MS with SMB is based on trading GC separation for speed of analysis while enhancing the separation power of the MS via the enhancement of the Molecular ion in the electron ionization of cold molecules in the SMB. This paper further discusses several features of fast GC and fast GC–MS and the various trade-offs involved in having powerful and practical fast GC–MS.
Alexander B Fialkov - One of the best experts on this subject based on the ideXlab platform.
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gc ms with photoionization of cold molecules in supersonic Molecular Beams approaching the softest ionization method
Journal of Mass Spectrometry, 2020Co-Authors: Alexander B Fialkov, Elias Ikonen, Tiina Laaksonen, Aviv AmiravAbstract:A new type of photoionization ion source was developed for the ionization of cold molecules in supersonic Molecular Beams (named Cold PI). The system was based on a GC-MS with supersonic Molecular Beams and its fly-through EI of cold molecules ion source (Cold EI) plus quadrupole mass analyzer. A continuously operated deuterium VUV photoionization lamp was added and placed above and between the supersonic nozzle and skimmer whereas the Cold EI ion source served only as a portion of the ion transfer ion optics. The supersonic nozzle and skimmer were voltage biased and the VUV light crossed the supersonic expansion about 10 mm from the nozzle. We obtained over three orders of magnitude enhancement in the relative abundance of the Molecular ion of squalane in Cold PI versus in photoionization of this compound as a thermal compound. Accordingly, we also proved that standard photoionization is not as soft ionization method as previously perceived for large compounds. We found that Cold PI is as soft as and possibly softer than field ionization; thus, it could be the softest known ionization method. The ionization yield was about 200-300 times weaker than with Cold EI yet our limit of detection was about 200 femtogram in SIM mode for cholesterol and pyrene which is reasonable. Practically, all hydrocarbons gave only Molecular ions with rather uniform response whereas alcohols gave some Molecular ions plus major fragment ions particularly with a loss of water (similarly to field ionization). We tested Cold PI in the GC-MS analysis of diesel fuels and analyzed the time averaged data for group type information. We also found that we can analyze the diesel fuels by fast under 20-s flow injection analysis in which the generated averaged mass spectrum of Molecular ions only could serve for the characterization of fuels.
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electron ionization lc ms with supersonic Molecular Beams the new concept benefits and applications
Journal of Mass Spectrometry, 2015Co-Authors: Boaz Seemann, Alexander B Fialkov, Tal Alon, Svetlana Tsizin, Aviv AmiravAbstract:A new type of electron ionization LC-MS with supersonic Molecular Beams (EI-LC-MS with SMB) is described. This system and its operational methods are based on pneumatic spray formation of the LC liquid flow in a heated spray vaporization chamber, full sample thermal vaporization and subsequent electron ionization of vibrationally cold molecules in supersonic Molecular Beams. The vaporized sample compounds are transferred into a supersonic nozzle via a flow restrictor capillary. Consequently, while the pneumatic spray is formed and vaporized at above atmospheric pressure the supersonic nozzle backing pressure is about 0.15 Bar for the formation of supersonic Molecular Beams with vibrationally cold sample molecules without cluster formation with the solvent vapor. The sample compounds are ionized in a fly-though EI ion source as vibrationally cold molecules in the SMB, resulting in 'Cold EI' (EI of vibrationally cold molecules) mass spectra that exhibit the standard EI fragments combined with enhanced Molecular ions. We evaluated the EI-LC-MS with SMB system and demonstrated its effectiveness in NIST library sample identification which is complemented with the availability of enhanced Molecular ions. The EI-LC-MS with SMB system is characterized by linear response of five orders of magnitude and uniform compound independent response including for non-polar compounds. This feature improves sample quantitation that can be approximated without compound specific calibration. Cold EI, like EI, is free from ion suppression and/or enhancement effects (that plague ESI and/or APCI) which facilitate faster LC separation because full separation is not essential. The absence of ion suppression effects enables the exploration of fast flow injection MS-MS as an alternative to lengthy LC-MS analysis. These features are demonstrated in a few examples, and the analysis of the main ingredients of Cannabis on a few Cannabis flower extracts is demonstrated. Finally, the advantages of EI-LC-MS with SMB are listed and discussed.
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Measurement and optimization of organic chemical reaction yields by GC–MS with supersonic Molecular Beams
Tetrahedron, 2012Co-Authors: Aviv Amirav, Alexander Gordin, Boaz Seemann, Youlia Hagooly, Shlomo Rozen, Bogdan Belgorodsky, Hanit Marom, Michael Gozin, Alexander B FialkovAbstract:Abstract A new type of gas chromatograph mass spectrometer (GC–MS) was used for semi-online monitoring of organic chemical reactions for their yield optimization, mechanism elucidation, and for obtaining information on the reaction products identity and purity. It was used with reaction mixtures without prior separation and purification as needed for NMR, thereby saving time and effort. Our unique GC–MS named 5975-SMB Supersonic GC–MS is based on GC interface with the MS with supersonic Molecular Beams (SMB) and on ionization of the sample molecules during their axial flight through an open electron ionization ion source as vibrationally cold molecules. GC–MS with SMB is demonstrated to significantly extend the range of compounds amenable for analysis, practically always giving Molecular ions, enabling effective fast GC–MS analysis, and providing elemental formulas via isotope abundance analysis with unit mass resolution quadrupole MS. In addition, it uniquely provides uniform response to all compounds, a feature, which is vital for the measurement of chemical reaction yields. In this manuscript, four different organic synthetic reactions were studied and are described. Based on the collected data, we were able to better understand how the reaction conditions should be optimized in order to maximize the yields and purity of target products. Consequently, we propose that GC–MS with SMB can serve as a novel tool for the fast optimization of chemical reactions.
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a low thermal mass fast gas chromatograph and its implementation in fast gas chromatography mass spectrometry with supersonic Molecular Beams
Journal of Chromatography A, 2011Co-Authors: Alexander B Fialkov, Mati Morag, Aviv AmiravAbstract:Abstract A new type of low thermal mass (LTM) fast gas chromatograph (GC) was designed and operated in combination with gas chromatography mass spectrometry (GC–MS) with supersonic Molecular Beams (SMB), including GC–MS–MS with SMB, thereby providing a novel combination with unique capabilities. The LTM fast GC is based on a short capillary column inserted inside a stainless steel tube that is resistively heated. It is located and mounted outside the standard GC oven on its available top detector port, while the capillary column is connected as usual to the standard GC injector and supersonic Molecular beam interface transfer line. This new type of fast GC–MS with SMB enables less than 1 min full range temperature programming and cooling down analysis cycle time. The operation of the fast GC–MS with SMB was explored and 1 min full analysis cycle time of a mixture of 16 hydrocarbons in the C10H22 up to C44H90 range was achieved. The use of 35 mL/min high column flow rate enabled the elution of C44H90 in less than 45 s while the SMB interface enabled splitless acceptance of this high flow rate and the provision of dominant Molecular ions. A novel compound 9-benzylazidanthracene was analyzed for its purity and a synthetic chemistry process was monitored for the optimization of the chemical reaction yield. Biodiesel was analyzed in jet fuel (by both GC–MS and GC–MS–MS) in under 1 min as 5 ppm fatty acid methyl esters. Authentic iprodion and cypermethrin pesticides were analyzed in grapes extract in both full scan mode and fast GC–MS–MS mode in under 1 min cycle time and explosive mixture including TATP, TNT and RDX was analyzed in under 1 min combined with exhibiting dominant Molecular ion for TATP. Fast GC–MS with SMB is based on trading GC separation for speed of analysis while enhancing the separation power of the MS via the enhancement of the Molecular ion in the electron ionization of cold molecules in the SMB. This paper further discusses several features of fast GC and fast GC–MS and the various trade-offs involved in having powerful and practical fast GC–MS.
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classical electron ionization mass spectra in gas chromatography mass spectrometry with supersonic Molecular Beams
Rapid Communications in Mass Spectrometry, 2008Co-Authors: Alexander Gordin, Alexander B Fialkov, Aviv AmiravAbstract:A major benefit of gas chromatography/mass spectrometry (GC/MS) with a supersonic Molecular beam (SMB) interface and its fly-through ion source is the ability to obtain electron ionization of vibrationally cold molecules (cold EI), which show enhanced Molecular ions. However, GC/MS with an SMB also has the flexibility to perform ‘classical EI’ mode of operation which provides mass spectra to mimic those in commercial 70 eV electron ionization MS libraries. Classical EI in SMB is obtained through simple reduction of the helium make-up gas flow rate, which reduces the SMB cooling efficiency; hence the vibrational temperatures of the molecules are similar to those in traditional EI ion sources. In classical EI-SMB mode, the relative abundance of the Molecular ion can be tuned and, as a result, excellent identification probabilities and very good matching factors to the NIST MS library are obtained. Classical EI-SMB with the fly-through dual cage ion source has analyte sensitivity similar to that of the standard EI ion source of a basic GC/MS system. The fly-through EI ion source in combination with the SMB interface can serve for cold EI, classical EI-SMB, and cluster chemical ionization (CCI) modes of operation, all easily exchangeable through a simple and quick change (not involving hardware). Furthermore, the fly-through ion source eliminates sample scattering from the walls of the ion source, and thus it offers full sample inertness, tailing-free operation, and no ion-molecule reaction interferences. It is also robust and enables increased column flow rate capability without affecting the sensitivity. Copyright © 2008 John Wiley & Sons, Ltd.
Alexander Gordin - One of the best experts on this subject based on the ideXlab platform.
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Measurement and optimization of organic chemical reaction yields by GC–MS with supersonic Molecular Beams
Tetrahedron, 2012Co-Authors: Aviv Amirav, Alexander Gordin, Boaz Seemann, Youlia Hagooly, Shlomo Rozen, Bogdan Belgorodsky, Hanit Marom, Michael Gozin, Alexander B FialkovAbstract:Abstract A new type of gas chromatograph mass spectrometer (GC–MS) was used for semi-online monitoring of organic chemical reactions for their yield optimization, mechanism elucidation, and for obtaining information on the reaction products identity and purity. It was used with reaction mixtures without prior separation and purification as needed for NMR, thereby saving time and effort. Our unique GC–MS named 5975-SMB Supersonic GC–MS is based on GC interface with the MS with supersonic Molecular Beams (SMB) and on ionization of the sample molecules during their axial flight through an open electron ionization ion source as vibrationally cold molecules. GC–MS with SMB is demonstrated to significantly extend the range of compounds amenable for analysis, practically always giving Molecular ions, enabling effective fast GC–MS analysis, and providing elemental formulas via isotope abundance analysis with unit mass resolution quadrupole MS. In addition, it uniquely provides uniform response to all compounds, a feature, which is vital for the measurement of chemical reaction yields. In this manuscript, four different organic synthetic reactions were studied and are described. Based on the collected data, we were able to better understand how the reaction conditions should be optimized in order to maximize the yields and purity of target products. Consequently, we propose that GC–MS with SMB can serve as a novel tool for the fast optimization of chemical reactions.
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classical electron ionization mass spectra in gas chromatography mass spectrometry with supersonic Molecular Beams
Rapid Communications in Mass Spectrometry, 2008Co-Authors: Alexander Gordin, Alexander B Fialkov, Aviv AmiravAbstract:A major benefit of gas chromatography/mass spectrometry (GC/MS) with a supersonic Molecular beam (SMB) interface and its fly-through ion source is the ability to obtain electron ionization of vibrationally cold molecules (cold EI), which show enhanced Molecular ions. However, GC/MS with an SMB also has the flexibility to perform ‘classical EI’ mode of operation which provides mass spectra to mimic those in commercial 70 eV electron ionization MS libraries. Classical EI in SMB is obtained through simple reduction of the helium make-up gas flow rate, which reduces the SMB cooling efficiency; hence the vibrational temperatures of the molecules are similar to those in traditional EI ion sources. In classical EI-SMB mode, the relative abundance of the Molecular ion can be tuned and, as a result, excellent identification probabilities and very good matching factors to the NIST MS library are obtained. Classical EI-SMB with the fly-through dual cage ion source has analyte sensitivity similar to that of the standard EI ion source of a basic GC/MS system. The fly-through EI ion source in combination with the SMB interface can serve for cold EI, classical EI-SMB, and cluster chemical ionization (CCI) modes of operation, all easily exchangeable through a simple and quick change (not involving hardware). Furthermore, the fly-through ion source eliminates sample scattering from the walls of the ion source, and thus it offers full sample inertness, tailing-free operation, and no ion-molecule reaction interferences. It is also robust and enables increased column flow rate capability without affecting the sensitivity. Copyright © 2008 John Wiley & Sons, Ltd.
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classical electron ionization mass spectra in gas chromatography mass spectrometry with supersonic Molecular Beams
Rapid Communications in Mass Spectrometry, 2008Co-Authors: Alexander Gordin, Alexander B Fialkov, Aviv AmiravAbstract:A major benefit of gas chromatography/mass spectrometry (GC/MS) with a supersonic Molecular beam (SMB) interface and its fly-through ion source is the ability to obtain electron ionization of vibrationally cold molecules (cold EI), which show enhanced Molecular ions. However, GC/MS with an SMB also has the flexibility to perform ‘classical EI’ mode of operation which provides mass spectra to mimic those in commercial 70 eV electron ionization MS libraries. Classical EI in SMB is obtained through simple reduction of the helium make-up gas flow rate, which reduces the SMB cooling efficiency; hence the vibrational temperatures of the molecules are similar to those in traditional EI ion sources. In classical EI-SMB mode, the relative abundance of the Molecular ion can be tuned and, as a result, excellent identification probabilities and very good matching factors to the NIST MS library are obtained. Classical EI-SMB with the fly-through dual cage ion source has analyte sensitivity similar to that of the standard EI ion source of a basic GC/MS system. The fly-through EI ion source in combination with the SMB interface can serve for cold EI, classical EI-SMB, and cluster chemical ionization (CCI) modes of operation, all easily exchangeable through a simple and quick change (not involving hardware). Furthermore, the fly-through ion source eliminates sample scattering from the walls of the ion source, and thus it offers full sample inertness, tailing-free operation, and no ion-molecule reaction interferences. It is also robust and enables increased column flow rate capability without affecting the sensitivity. Copyright © 2008 John Wiley & Sons, Ltd.
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gas chromatography mass spectrometry with supersonic Molecular Beams
Journal of Mass Spectrometry, 2008Co-Authors: Aviv Amirav, Marina Poliak, Alexander Gordin, Alexander B FialkovAbstract:Gas chromatography-mass spectrometry (GC-MS) with supersonic Molecular Beams (SMBs) (also named Supersonic GC-MS) is based on GC and MS interface with SMBs and on the electron ionization (EI) of vibrationally cold analytes in the SMBs (cold EI) in a fly-through ion source. This ion source is inherently inert and further characterized by fast response and vacuum background filtration capability. The same ion source offers three modes of ionization including cold EI, classical EI and cluster chemical ionization (CI). Cold EI, as a main mode, provides enhanced Molecular ions combined with an effective library sample identification, which is supplemented and complemented by a powerful isotope abundance analysis method and software. The range of low-volatility and thermally labile compounds amenable for analysis is significantly increased owing to the use of the contact-free, fly-through ion source and the ability to lower sample elution temperatures through the use of high column carrier gas flow rates. Effective, fast GC-MS is enabled particularly owing to the possible use of high column flow rates and improved system selectivity in view of the enhancement of the Molecular ion. This fast GC-MS with SMB can be further improved via the added selectivity of MS-MS, which by itself benefits from the enhancement of the Molecular ion, the most suitable parent ion for MS-MS. Supersonic GC-MS is characterized by low limits of detection (LOD), and its sensitivity is superior to that of standard GC-MS, particularly for samples that are hard for analysis. The GC separation of the Supersonic GC-MS can be improved with pulsed flow modulation (PFM) GC x GC-MS. Electron ionization LC-MS with SMB can also be combined with the Supersonic GC-MS, with fast and easy switching between these two modes of operation.
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gas chromatography mass spectrometry with supersonic Molecular Beams
Journal of Mass Spectrometry, 2008Co-Authors: Aviv Amirav, Marina Poliak, Alexander Gordin, Alexander B FialkovAbstract:A new approach for liquid chromatography mass spectrometry (LC-MS) is described, based on achieving soft thermal vaporization followed by supersonic expansion and direct sample compound ionization, while in a supersonic Molecular beam (SMB). The soft Molecular vaporization step utilizes spray formation that is continued by fast thermal vaporization inside a channel supersonic nozzle, followed by ultrafast supercooling in a supersonic expansion. The short time (several microseconds) spent by the vaporized compound in the heated nozzle prior to its expansion cooling may result in incomplete vibrational equilibrium and thus reduced degree of dissociation. In addition, even if vibrational equilibrium at the nozzle temperature is obtained, the sample compounds have significantly reduced time for their dissociation, which is thus further minimized (kinetic consideration). As soon as the molecules expand and form a SMB, they are supercooled and any further dissociation is avoided. While in the SMB, the sample molecules can be ionized either by electron ionization as described in this paper or by hyperthermal surface ionization. The major goal of this method is to obtain high quality library searchable electron ionization mass spectra, for a broad range of thermally labile compounds, with higher sensitivity than that achievable by particle beam LC-MS. The soft thermal vaporization nozzle is described and mass spectral results with corticosterone are demonstrated. The potential advantageous features of this new method are discussed.
Shai Dagan - One of the best experts on this subject based on the ideXlab platform.
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fast very fast and ultra fast gas chromatography mass spectrometry of thermally labile steroids carbamates and drugs in supersonic Molecular Beams
Journal of the American Society for Mass Spectrometry, 1996Co-Authors: Shai Dagan, Aviv AmiravAbstract:Gas chromatography-mass spectrometry (GC-MS) analyses of thermally labile compounds have been studied by using a short column fast gas chromatograph, coupled with fly-through electron ionization in supersonic Molecular Beams. Thirty-two compounds, which include steroids, carbamate pesticides, antibiotic drugs, and other pharmaceutical compounds, have been analyzed and the details of their GC-MS analysis are provided. The ability to analyze thermally labile compounds is discussed in relation to the speed of analysis. A new term, “speed enhancement factor” (SEF), is defined as the product of column length reduction and the carrier gas linear velocity increase, as compared with normal GC-MS conditions. Fast, very fast, and ultra-fast GC-MS are defined with a SEF in the ranges of 5–30, 30–400, and 400–4000, respectively. Trade-offs in the degree of dissociation, speed, gas chromatograph resolution, and sensitivity were studied and examined with thermally labile molecules. The experimental factors that affect the dissociation are described with emphasis on its reduction. We claim that the use of supersonic Molecular Beams for sampling and ionization provides the ultimate capability in the GC-MS of thermally labile compounds. The obtained 70-eV electron ionization mass spectra are shown, and an enhanced relative abundance of the Molecular ion is demonstrated together with library search capability of these mass spectra, which is better than that reported with particle beam liquid chromatography-mass spectrometry. The performance of fast GC-MS in supersonic Molecular Beams is compared with other methods of fast GC-MS and with particle beam liquid chromatography-mass spectrometry.
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cluster chemical ionization and deuterium exchange mass spectrometry in supersonic Molecular Beams
Journal of the American Society for Mass Spectrometry, 1996Co-Authors: Shai Dagan, Aviv AmiravAbstract:A cluster-based chemical ionization method has been developed that produces protonated Molecular ions from molecules introduced through a supersonic Molecular beam interface. Mixed clusters of the analyte and a clustering agent (water or methanol) are produced in the expansion region of the beam, and are subsequently ionized by “fly through” electron impact (EI) ionization, which results in a mass spectrum that is a combination of protonated Molecular ion peaks together with the conventional EI fragmentation pattern. The technique is presented and discussed as a tool complementary to electron impact ionization in supersonic Molecular Beams. Surface-induced dissociation on a rhenium oxide surface is also applied to simplify the mass spectra of clusters and reveal the analyte spectrum. The high gas flow rates involved with the supersonic Molecular beam interface that enable the easy introduction of the clustering agents also have been used to introduce deuterating agents. An easy-to-use, fast, and routine on-line deuterium exchange method was developed to exchange active hydrogens (NH, OH). This method, combined with electron impact ionization, is demonstrated and discussed in terms of the unique information available through the EI fragmentation patterns, its ability to help in isomer identification, and possible applications with fast gas chromatography-mass spectrometry in supersonic Molecular Beams.
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Electron impact mass spectrometry of alkanes in supersonic Molecular Beams
Journal of the American Society for Mass Spectrometry, 1995Co-Authors: Shai Dagan, Aviv AmiravAbstract:The electron impact mass spectrometry of straight chain alkanes C_8H_18-C_40H_82, squalane, methylstearate, 1-chlorohexadecane, 1-bromohexadecane, and dioctylphthalate was studied by sampling them with supersonic Molecular Beams. A fly-through Brink-type electron impact ion source was used, utilizing a vacuum background ion filtration technique based on differences between the kinetic energy of the supersonic beam species and that of thermal molecules. The 70-eV electron impact mass spectra of all the alkanes were characterized by a pronounced or dominant Molecular weight peak together with all the fragment ions normally exhibited by the standard thermal 70-eV EI mass spectra. In contrast, the NIST library of most of these molecules did not show any Molecular weight peak. By eliminating tile intraMolecular thermal vibrational energy we gained control over the degree of Molecular ion fragmentation by the electron energy. At an electron energy of 18 eV the Molecular ion dissociation was further reduced considerably, with only a small absolute reduction in the peak height by less than a factor of 2. The effect of vibrational cooling increased with the Molecular size and number of atoms. Pronounced differences were observed between the mass spectra of the straight chain triacontane and its branched isomer squalane. Similar mass spectra of octacosane (C_28H_58) achieved with 70-eV EI in a supersonic Molecular beam were obtained with a magnetic sector mass spectrometer by using an electron energy of 14 eV and an ion source temperature of 150 °C. However, this ion source temperature precluded the gas chromatography-mass spectrometry (GC-MS) of octacosane. The GC-MS of alkanes was studied with an ion trap gas chromatograph-mass spectrometer at an ion source temperature of 230 °C. Thermal peak tailing was observed for C_20H_42 and heavier alkanes, whereas for C_28H_58 and heavier alkanes the severe peak tailing made quantitative GC-MS impractical. In contrast, no peak tailing existed even with C_40H_82 for GC-MS in supersonic Molecular Beams. The minimum detected amount of eicosane (C_20, H_42) was shown to be 60 fg. This was demonstrated by using single ion monitoring with the quadrupole mass analyzer tuned to the Molecular weight peak of 282 u. The coupling of electron impact mass spectrometry in supersonic Molecular Beams with hyperthermal surface ionization and a fast GC-MS inlet is briefly discussed.
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fast high temperature and thermolabile gc ms in supersonic Molecular Beams
International Journal of Mass Spectrometry and Ion Processes, 1994Co-Authors: Shai Dagan, Aviv AmiravAbstract:Abstract This work describes and evaluates the coupling of a fast gas chromatograph (GC) based on a short column and high carrier gas flow rate to a supersonic Molecular beam mass spectrometer (MS). A 50 cm long megabore column serves for fast GC separation and connects the injector to the supersonic nozzle source. Sampling is achieved with a conventional syringe based splitless sample injection. The injector contains no septum and is open to the atmosphere. The linear velocity of the carrier gas is controlled by a by-pass (make-up) gas flow introduced after the column and prior to the supersonic nozzle. The supersonic expansion serves as a jet separator and the skimmed supersonic Molecular beam (SMB) is highly enriched with the heavier organic molecules. The supersonic Molecular beam constituents are ionized either by electron impact (EI) or hyperthermal surface ionization (HSI) and mass analyzed. A 1 s fast GC—MS of four aromatic molecules in methanol is demonstrated and some fundamental aspects of fast GC—MS with time limit constraints are outlined. The flow control (programming) of the speed of analysis is shown and the analysis of thermolabile and relatively non-volatile molecules is demonstrated and discussed. The tail-free, fast GC—MS of several mixtures is shown and peak tailing of caffeine is compared with that of conventional GC—MS. The improvement of the peak shapes with the SMB—MS is analyzed with the respect to the elimination of thermal vacuum chamber background. The extrapolated minimum detected amount was about 400 ag of anthracence- d 10 , with an elution time which was shorter than 2s. Repetitive injections could be performed within less than 10 s. The fast GC—MS in SMB seems to be ideal for fast target compound analysis even in real world, complex mixtures. The few seconds GC—MS separation and quantification of lead (as tetraethyllead) in gasoline, caffeine in coffee, and codeine in a drug is demonstrated. Controlled HSI selectivity is demonstrated in the range of 10 1 to 10 4 anthracene/decane which helped to simplify the selective analysis of aromatic molecules in gasoline. The contribution of SMB to the operation of the fast GC—MS is summarized and the compatibility with conventional GC having a megabore column is shown. Splitless injections of 100 μL sample solutions for trace level concentration detection is also presented (with a conventional GC).
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Proposal for Laser Cooling of Complex Polyatomic Molecules.
Chemphyschem : a European journal of chemical physics and physical chemistry, 2016Co-Authors: Ivan Kozyryev, Louis Baum, Kyle Matsuda, John M DoyleAbstract:An experimentally feasible strategy for direct laser cooling of polyatomic molecules with six or more atoms is presented. Our approach relies on the attachment of a metal atom to a complex molecule, where it acts as an active photon cycling site. We describe a laser cooling scheme for alkaline earth monoalkoxide free radicals taking advantage of the phase space compression of a cryogenic buffer-gas beam. Possible applications are presented including laser cooling of chiral molecules and slowing of Molecular Beams using coherent photon processes.
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intense atomic and Molecular Beams via neon buffer gas cooling
New Journal of Physics, 2009Co-Authors: David Patterson, Julia Rasmussen, John M DoyleAbstract:We realize a continuous, intense, cold Molecular and atomic beam source based on buffer-gas cooling. Hot vapor (up to 600 K) from an oven is mixed with cold (15 K) neon buffer gas, and then emitted into a high-flux beam. The novel use of cold neon as a buffer gas produces a forward velocity distribution and low-energy tail that is comparable to much colder helium-based sources. We expect this source to be trivially generalizable to a very wide range of atomic and Molecular species with significant vapor pressure below 1000 K. The source has properties that make it a good starting point for laser cooling of molecules or atoms, cold collision studies, trapping, or nonlinear optics in buffer-gas-cooled atomic or Molecular gases. A continuous guided beam of cold deuterated ammonia with a flux of 3×1011 ND3 molecules s−1 and a continuous free-space beam of cold potassium with a flux of 1×1016 K atoms s−1 are realized.
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intense atomic and Molecular Beams via neon buffer gas cooling
arXiv: Atomic Physics, 2008Co-Authors: David Patterson, Julia Rasmussen, John M DoyleAbstract:We realize a continuous guided beam of cold deuterated ammonia with a flux of 3e11 ND3 molecules/s and a continuous free-space beam of cold potassium with a flux of 1e16 K atoms/s. A novel feature of the buffer gas source used to produce these Beams is cold neon, which, due to intermediate Knudsen number beam dynamics, produces a forward velocity and low-energy tail that is comparable to much colder helium-based sources. We expect this source to be trivially generalizable to a very wide range of atomic and Molecular species with significant vapor pressure below 1000 K. This source has properties that make it a good starting point for laser cooling of molecules or atoms, cold collision studies, trapping, or nonlinear optics in buffer-gas-cooled atomic or Molecular gases.
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buffer gas cooling of atomic and Molecular Beams
Physical Review A, 2002Co-Authors: Dima Egorov, Bretislav Friedrich, Wieland Schöllkopf, Thierry Lahaye, John M DoyleAbstract:We demonstrate direct loading and cooling of a thermal beam into a cryogenic helium buffer gas. Our test species is rubidium; we observe a thermal beam with $3\ifmmode\times\else\texttimes\fi{}{10}^{13}{\mathrm{s}}^{\ensuremath{-}1}$ flux entering a cryocell and thermalizing with a 4.2-K buffer gas. There is no evidence of clustering or other spurious loss mechanisms. The cooling technique should be applicable to a wide variety of species, including radicals.