1
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Elkabets O, Neumark B, Amirav A. Sample Injection for Real-Time Analysis (SIRTA) Using GC-MS with Cold EI. J Am Soc Mass Spectrom 2024; 35:378-385. [PMID: 38234102 PMCID: PMC10853959 DOI: 10.1021/jasms.3c00412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/29/2023] [Revised: 12/26/2023] [Accepted: 01/03/2024] [Indexed: 01/19/2024]
Abstract
There is a continual demand for advanced methods and instruments for real-time analysis (RTA). Most of the current RTA techniques based on MS involve ambient desorption ionization technology. However, flow injection of liquid extracted samples is another option without added modifications or cost to existing LC-MS instruments. In this work, we introduce a new RTA approach named sample injection for real-time analysis (SIRTA) using GC-MS with Cold EI. In SIRTA, the standard GC column is replaced with a 1 m long 0.1 mm I.D. fused silica capillary that connects the GC injector to the MS transfer-line of Cold EI. Thus, SIRTA with Cold EI imposes no need for any additional instrumentation; hence, it is characterized by zero added cost. Like in flow injection in MS of LC-MS, the sample is dissolved in ∼1 mL methanol or another solvent. Subsequently, the vial is placed in the GC-MS autosampler while using a standard syringe for injection without any GC separation. The analysis takes merely 0.2-0.7 min, ensuring rapid and consecutive analyses. Unlike standard EI, Cold EI enables SIRTA by taking advantage of its fly through open ion source to avoid overwhelming the ion source during the elution of solvents while still providing enhanced molecular ions for nearly all analytes. In this study, we demonstrated SIRTA Cold EI analysis of 12 compounds and 7 mixtures, including various prescription and illicit drugs, cannabis and petroleum samples, and other synthetic organic compounds including those with molecular weight up to 800 g/mol.
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Affiliation(s)
- Oneg Elkabets
- School
of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel
| | - Benny Neumark
- School
of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel
| | - Aviv Amirav
- School
of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel
- Aviv
Analytical Ltd, 24 Hanagar
Street, Hod Hasharon 4527713, Israel
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2
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Elkabets O, Neumark B, Amirav A. Fast saliva analysis by GC-MS with Cold EI and Open Probe Fast GC-MS with Cold EI for the detection of cannabis usage. J Mass Spectrom 2023; 58:e4981. [PMID: 37950648 DOI: 10.1002/jms.4981] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2023] [Revised: 10/03/2023] [Accepted: 10/11/2023] [Indexed: 11/13/2023]
Abstract
Saliva is a body fluid that is much easier to collect and analyze than blood. Thus, saliva analysis for the detection of delta 9-tetrahydrocannabinol (delta 9-THC) can serve as a tool for law enforcement agents to detect cannabis consumption by drivers. Fast saliva analysis for the presence of delta 9-THC and/or cannabidiol (CBD) is described with both gas chromatography-mass spectrometry (GC-MS) with Cold electron ionization (EI) with good separation and in 10 min and/or with Open Probe Fast GC-MS with Cold EI in under 1 min full analysis cycle time. Saliva was taken directly from donors' tongues on a thin glass rod that was used "as is" for analysis. The saliva was thermally desorbed with a modified ChromatoProbe device inside the gas chromatograph (GC) injector and in an Open Probe (Agilent name QuickProbe) for its sub-1-min analysis. Cold EI is based on coupling of the GC and mass spectrometer (MS) with a supersonic molecular beam and on EI of vibrationally cold sample molecules during their flight through a contact-free ion source (thereby named Cold EI). A revised type of Open Probe Fast GC-MS on the bench is also described. Our saliva analysis was characterized by: Saliva can be collected in the field and transported to the lab for analyses "as is" without any sample preparation. Easy detection of cannabis consumption from cigarettes and/or other cannabis products. Distinction between the isomers delta 9-THC and CBD. Ultra-fast analysis in under 1 min using Open Probe Fast GC-MS with Cold EI.
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Affiliation(s)
- Oneg Elkabets
- School of Chemistry, Tel Aviv University, Tel Aviv, Israel
| | - Benny Neumark
- School of Chemistry, Tel Aviv University, Tel Aviv, Israel
| | - Aviv Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv, Israel
- Aviv Analytical Ltd, Hod Hasharon, Israel
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3
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Amirav A, Yakovchuk A. Sensitivity comparison of gas chromatography-mass spectrometry with Cold EI and standard EI. J Mass Spectrom 2023; 58:e4950. [PMID: 37271583 DOI: 10.1002/jms.4950] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Received: 03/12/2023] [Revised: 05/03/2023] [Accepted: 05/13/2023] [Indexed: 06/06/2023]
Abstract
Gas chromatography-mass spectrometry (GC-MS) with Cold EI is based on interfacing GC and MS with supersonic molecular beams (SMBs) along with electron ionization of vibrationally cold sample compounds in SMB in a fly-through ion source (hence the name Cold EI). Cold EI improves all the central performance aspects of GC-MS, and in this paper, we focus on its improvement of signal-to-noise ratio (S/N) and limits of detection (LODs). We found that the harder the compound for analysis with standard EI, the greater the Cold EI gain in S/N and LOD. The lower LOD and higher S/N of Cold EI emerge from a few reasons: (a) similar ionization yield as standard EI, (b) enhanced abundance of molecular ions, (c) elimination of vacuum background noise, (d) elimination of ion source-related peak tailing and degradation, (e) ability to lower the elution temperatures via the use of high column flow rates, and (f) greater range of thermally labile and low-volatility compounds that can be analyzed. We demonstrate the superior S/N and lower LOD of Cold EI versus standard EI in a range of compounds, from the simple-to-analyze octafluoronaphthalene all the way to reserpine and an organo-metallic compound that cannot be analyzed by standard EI. These compounds include methyl stearate, cholesterol, n-C32 H66 , large polycyclic aromatic hydrocarbons, dioctyl phthalates, diundecyl phthalate, pentachlorophenol, benzidine, lambda-cyhalothrin, and methidathion. The significantly lower Cold EI LODs that can be over 1000 times better than in standard EI further result in far superior response linearity and greater measurement dynamic range.
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Affiliation(s)
- Aviv Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv, Israel
- Aviv Analytical Ltd, Hod Hasharon, Israel
| | - Alex Yakovchuk
- School of Chemistry, Tel Aviv University, Tel Aviv, Israel
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4
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Neumark B, Elkabets O, Shefer G, Buch A, Stern N, Amirav A. Whole blood analysis for medical diagnostics by GC-MS with Cold EI. J Mass Spectrom 2022; 57:e4873. [PMID: 35796286 PMCID: PMC9540862 DOI: 10.1002/jms.4873] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/06/2022] [Revised: 06/19/2022] [Accepted: 06/26/2022] [Indexed: 06/15/2023]
Abstract
This study covers a new method and related instrumentation for whole blood analysis for medical diagnostics. Two-μL whole blood samples were collected using "minimal invasive" diabetes lancet and placed on a thin glass rod mounted on a newly designed BloodProbe. The BloodProbe with the whole blood sample was inserted directly into a ChromatoProbe mounted on the GC inlet, and thus, no sample preparation was involved. The analysis was performed within 10 min using a GC-MS with Cold EI that is based on interfacing GC and MS with supersonic molecular beams (SMB) along with electron ionization of vibrationally cold sample compounds in the SMB (hence the name Cold EI). Our blood analysis revealed several observations: (1) Detailed mass chromatograms were generated with full range of all the nonpolar lipids in blood including fatty acids, cholesterol, cholesteryl esters, vitamin E, monoglycerides, diglycerides, and triglycerides. (2) The analysis of whole blood was found to be as informative as the conventional clinical analysis of blood serum. (3) Cholesteryl esters were more sensitive than free cholesterol alone to the effect of diet of obese people. (4) Major enhancement of several fatty acid methyl esters was found in the blood of a cancer patient with liver dysfunction. (5) Vitamin E as both α- and β-tocopherol was found with person-dependent ratio of these two compounds. (6) Elemental sulfur S8 was identified in blood. (7) Several drugs and other compounds were found and need further study of their correlation to medical issues.
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Affiliation(s)
- Benny Neumark
- School of ChemistryTel Aviv UniversityTel AvivIsrael
| | - Oneg Elkabets
- School of ChemistryTel Aviv UniversityTel AvivIsrael
| | - Gabi Shefer
- The Institute of Endocrinology, Metabolism and HypertensionTel‐Aviv Sourasky Medical CenterTel AvivIsrael
| | - Assaf Buch
- The Institute of Endocrinology, Metabolism and HypertensionTel‐Aviv Sourasky Medical CenterTel AvivIsrael
| | - Naftali Stern
- The Institute of Endocrinology, Metabolism and HypertensionTel‐Aviv Sourasky Medical CenterTel AvivIsrael
- The Sagol Center for Epigenetics of Aging and MetabolismTel‐Aviv Sourasky Medical CenterTel AvivIsrael
- Sackler Faculty of MedicineTel Aviv UniversityTel AvivIsrael
| | - Aviv Amirav
- School of ChemistryTel Aviv UniversityTel AvivIsrael
- Aviv AnalyticalHod HasharonIsrael
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5
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Margolin Eren KJ, Prest HF, Amirav A. Nitrogen and hydrogen as carrier and make-up gases for GC-MS with Cold EI. J Mass Spectrom 2022; 57:e4830. [PMID: 35472728 PMCID: PMC9285341 DOI: 10.1002/jms.4830] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/10/2022] [Accepted: 04/15/2022] [Indexed: 06/14/2023]
Abstract
Gas chromatography-mass spectrometry (GC-MS) with Cold EI is based on interfacing GC and MS with a supersonic molecular beam (SMB) and sample compounds ionization with a fly-through ion source as vibrationally cold compounds in the SMB (hence the name Cold EI). We explored the use of nitrogen and hydrogen as carrier and make-up gases with Cold EI and found: Nitrogen is very effective in cooling compounds in SMB and while helium requires 60 ml/min nitrogen provides effective cooling with only 7-8 ml/min combined column and make-up flow rate. Hydrogen is less effective than helium and requires higher flow rates. The transition from helium to nitrogen (or hydrogen) is simple and fast and requires just closing the helium valve and opening the nitrogen valve. The same column used with helium can be used with nitrogen or hydrogen. The same elution times could be obtained with nitrogen or hydrogen as with helium. The GC separation with nitrogen was reduced compared with helium and peak widths were increased by an average factor of 1.5 for similar elution times. Hydrogen provided ~0.7 narrower peak widths than helium. The signal with nitrogen was reduced compared with helium by an average factor of 3.3 and the signal loss was reduced with higher compounds mass. With hydrogen the signal loss was about a factor of 1.5 but the baseline noise was higher thus with similar S/N as with nitrogen. USEPA 8270 semivolatile mixture was easily analyzed with both nitrogen and hydrogen carrier gases.
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Affiliation(s)
| | | | - Aviv Amirav
- School of ChemistryTel Aviv UniversityTel AvivIsrael
- Aviv Analytical LtdHod HasharonIsrael
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6
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Amirav A, Fialkov AB, Gordin A, Elkabets O, Margolin Eren KJ. Cold Electron Ionization (EI) Is Not a Supplementary Ion Source to Standard EI. It is a Highly Superior Replacement Ion Source. J Am Soc Mass Spectrom 2021; 32:2631-2635. [PMID: 34652909 PMCID: PMC8589250 DOI: 10.1021/jasms.1c00241] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/15/2021] [Revised: 09/30/2021] [Accepted: 10/01/2021] [Indexed: 06/13/2023]
Abstract
GC-MS usually employs a 70 eV electron ionization (EI) ion source, which provides mass spectra with detailed fragment ion information that are amenable for library search and identification with names and structures at the isomer level. However, conventional EI often suffers from low intensity or the absence of molecular ions, which reduces detection and identification capabilities in analyses. In an attempt to enhance the molecular ions, several softer ion sources are being used to supplement standard EI, including chemical ionization (CI), atmospheric pressure chemical ionization (APCI), field ionization (FI), photoionization (PI), and low electron energy EI. However, the most advantageous way to enhance molecular ions is to use cold EI, which employs 70 eV EI of cold molecules in supersonic molecular beams. Cold EI yields classical EI mass spectra with highly enhanced molecular ions, which still provides high detectability and library-searchable mass spectra. In this paper, we explain and discuss why cold EI is not a supplementary ion source to standard EI, but rather it is a highly superior replacement to standard EI. With cold EI, there is no need for standard EI or any other supplemental ion source. We describe 16 benefits and unique features of cold EI that not only yield better results for existing applications but also significantly extend the range of compounds and applications amenable for GC-MS analysis.
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Affiliation(s)
- Aviv Amirav
- School
of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel
- Aviv
Analytical Ltd., 24 Hanagar
Street, Hod Hasharon 4527713, Israel
| | | | - Alexander Gordin
- School
of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel
| | - Oneg Elkabets
- School
of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel
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7
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Amirav A, Neumark B, Margolin Eren KJ, Fialkov AB, Tal N. Cannabis and its cannabinoids analysis by gas chromatography-mass spectrometry with Cold EI. J Mass Spectrom 2021; 56:e4726. [PMID: 33955098 DOI: 10.1002/jms.4726] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Revised: 03/14/2021] [Accepted: 03/15/2021] [Indexed: 06/12/2023]
Abstract
Cannabis extracts and products were analyzed by gas chromatography-mass spectrometry (GC-MS) with Cold EI for their full content including terpenes, sesquiterpenes, sesquiterpinols, fatty acids, delta 9-tetrahydrocannabinol (THC), cannabidiol (CBD), other cannabinoids, hydrocarbons, sterols, diglycerides, triglycerides, and impurities. GC-MS with Cold EI is based on interfacing GC and MS with supersonic molecular beams (SMB) along with electron ionization of vibrationally cold sample compounds in the SMB in a fly-through ion source (hence the name Cold EI). GC-MS with Cold EI improves all the performance aspects of GC-MS, enables the analysis of Cannabinoids with OH groups without derivatization, while providing enhanced molecular ions for improved identification, and enables internal quantitation without calibration. We found over 50 cannabinoid compounds including a new one with a Cold EI mass spectrum very similar to delta 9-THC as well as relatively large cannabinoids with molecular weight above m/z = 400. Because the analysis was universal in full scan and not targeted, we found impurities such as bromo CBD and fluticasone propionate and could monitor the formation of oxidized CBD during decarboxylation. In addition, GC-MS with Cold EI enabled nontargeted full analysis of terpenes, sesquiterpenes, and sesquiterpinols in cannabis extracts with good internal quantitation. GC-MS with Cold EI further served with very good sensitivity for the concentration determination of delta 9-THC in CBD-related products. Finally, cannabis drugs such as EP-1 used in Israel for treatment of epilepsy and for children with autism spectrum disorder (ASD) were analyzed for their full cannabinoids content for learning on the entourage effect and for drug activity optimization.
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Affiliation(s)
- Aviv Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv, Israel
- Aviv Analytical Ltd, Hod Hasharon, Israel
| | - Benny Neumark
- School of Chemistry, Tel Aviv University, Tel Aviv, Israel
| | | | | | - Noam Tal
- School of Chemistry, Tel Aviv University, Tel Aviv, Israel
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8
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Alon T, Amirav A. Comparison of Isotope Abundance Analysis and Accurate Mass Analysis in their Ability to Provide Elemental Formula Information. J Am Soc Mass Spectrom 2021; 32:929-935. [PMID: 33779170 PMCID: PMC8154599 DOI: 10.1021/jasms.0c00419] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Revised: 03/09/2021] [Accepted: 03/09/2021] [Indexed: 06/12/2023]
Abstract
Deriving elemental formulas from mass spectra used to be an exclusive feature provided only by expensive high-resolution mass spectrometry instruments. Nowadays this feature can be used on unit resolution quadrupole-based mass spectrometers (MS) combining isotope abundance analysis (IAA) and mass accuracy analysis (MAA) with surprising accuracy that is commonly lower than 1 ppm mass accuracy. In this Article, we assess the usefulness of both MAA and IAA in the elemental formula deriving process performed on unit resolution MS data with constant resolution across the m/z range. The methods' effective filtration power (EFP) are estimated along with their ability to provide useful elemental information under nonideal experimental conditions. The term effective mass accuracy (EMA) is introduced so that the identification power of IAA can be expressed in a familiar way and compared more readily to MAA. We found that IAA alone commonly has an EMA under 5 ppm. IAA and MAA work well together and provide improved results with median EMA < 1 ppm for calibrated MS or <3 ppm for uncalibrated MS. We have also found that even though these methods cannot be fully trusted to pinpoint the exact elemental formula under poor experimental conditions, IAA can still accurately provide the exact number of several heteroatoms such as sulfur, chlorine, and bromine, while MAA cannot. Under such conditions, a combination of both methods can also provide good insight into the amount of carbon, hydrogen, and other elements in the elemental formula.
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Affiliation(s)
- Tal Alon
- School
of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel
- Afeka
School of Engineering, Tel Aviv, 6910717, Israel
- Aviv
Analytical Ltd., 24 Hanagar
Street, Hod Hasharon, 4527713, Israel
| | - Aviv Amirav
- School
of Chemistry, Tel Aviv University, Tel Aviv 6997801, Israel
- Aviv
Analytical Ltd., 24 Hanagar
Street, Hod Hasharon, 4527713, Israel
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9
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Margolin Eren KJ, Elkabets O, Amirav A. A comparison of electron ionization mass spectra obtained at 70 eV, low electron energies, and with cold EI and their NIST library identification probabilities. J Mass Spectrom 2020; 55:e4646. [PMID: 32996658 DOI: 10.1002/jms.4646] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 08/05/2020] [Accepted: 08/11/2020] [Indexed: 06/11/2023]
Abstract
Electron ionization (EI) mass spectra of 46 compounds from several different compound classes were measured. Their molecular ion abundances were compared as obtained with 70-eV EI, with low eV EI (such as 14 eV), and with EI mass spectra of vibrationally cold molecules in supersonic molecular beams (Cold EI). We further compared these mass spectra in their National Institute of Standards and Technology (NIST) library identification probabilities. We found that Low eV EI is not a soft ionization method, and it has little or no influence on the molecular ion relative abundances for large molecules and those with weak or no molecular ions. Low eV EI for compounds with abundant or dominant molecular ions in their 70 eV mass spectra results in the reduction of low mass fragment ions abundances thereby reducing their NIST library identification probabilities thus rarely justifies its use in real-world applications. Cold EI significantly enhances the relative abundance of the molecular ions particularly for large compounds; yet, it retains the low mass fragment ions; hence, Cold EI mass spectra can be effectively identified by the NIST library. Different standard EI ion sources provide different 70 eV EI mass spectra. Among the Agilent technologies ion sources, the "Extractor" exhibits relatively abundant molecular ions compared with the "Inert" ion source, while the "High efficiency source" (HES) provides mass spectra with depleted molecular ions compared with the "Inert" ion source or NIST library mass spectra. These conclusions are demonstrated and supported by experimental data in nine figures and two tables.
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Affiliation(s)
| | - Oneg Elkabets
- School of Chemistry, Tel Aviv University, Tel Aviv, 6997801, Israel
| | - Aviv Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv, 6997801, Israel
- Aviv Analytical LTD, 24 Hanagar Street, Hod Hasharon, 4527713, Israel
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10
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Tsizin S, Fialkov AB, Amirav A. Analysis of impurities in pharmaceuticals by LC-MS with cold electron ionization. J Mass Spectrom 2020; 55:e4587. [PMID: 32662574 DOI: 10.1002/jms.4587] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 06/08/2020] [Accepted: 06/08/2020] [Indexed: 06/11/2023]
Abstract
Pharmaceuticals require careful and precise determination of their impurities that might harm the user upon consumption. Although today, the most common technique for impurities identification is liquid chromatography-mass spectrometry (LC-MS/MS), it has several downsides due to the nature of the ionization method. Also, the analyses in many cases are targeted thus despite being present, some of the compounds will not be revealed. In this paper, we propose and show a new method for untargeted analysis and identification of impurities in active pharmaceutical ingredients (APIs). The instrument used for these analyses is a novel electron ionization (EI) LC-MS with supersonic molecular beams (SMB). The EI-LC-MS-SMB was implemented for analyses of several drug samples spiked with an impurity. The instrument provides EI mass spectra with enhanced molecular ions, named Cold EI, which increases the identification probabilities when the compound is identified with the aid of an EI library like National Institute of Standards and Technology (NIST). We analyzed ibuprofen and its impurities, and both the API and the expected impurity were identified with names and structures by the NIST library. Moreover, other unexpected impurities were found and identified proving the ability of the EI-LC-MS-SMB system for truly untargeted analysis. The results show a broad dynamic range of four orders of magnitude at the same run with a signal-to-noise ratio of over 10 000 for the API and almost uniform response.
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Affiliation(s)
- Svetlana Tsizin
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
| | | | - Aviv Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
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11
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Fialkov AB, Ikonen E, Laaksonen T, Amirav A. GC-MS with photoionization of cold molecules in supersonic molecular beams-Approaching the softest ionization method. J Mass Spectrom 2020; 55:e4516. [PMID: 32567120 DOI: 10.1002/jms.4516] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Revised: 03/18/2020] [Accepted: 03/23/2020] [Indexed: 06/11/2023]
Abstract
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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Affiliation(s)
| | | | | | - Aviv Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
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12
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Tsizin S, Fialkov AB, Amirav A. Electron Ionization Mass Spectrometry for Both Liquid and Gas Chromatography in One System without the Need for Hardware Adjustments. J Am Soc Mass Spectrom 2020; 31:1713-1721. [PMID: 32543199 DOI: 10.1021/jasms.0c00136] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
A new instrument that bridges the gap between gas chromatography (GC) and liquid chromatography (LC) mass spectrometry (MS) was developed. In this instrument GC-MS and electron ionization LC-MS were combined in one MS system with method based mode changing. The LC pneumatic spray formation interface to MS was mounted on top of an otherwise unused GC detector slot and was connected with a flow restriction capillary to the MS through the GC oven and into the MS transfer line, parallel to the GC capillary column. The LC output mobile phase flow is directed into a spray formation and vaporization chamber. The pneumatic spray results in fine spray droplets that are thermally vaporized at a pressure equal to or greater than ambient. A portion of the vaporized mixture is directed into the heated flow restriction capillary that connects the spray formation and vaporization chamber into the electron ionization (EI) ion source, while most of the vaporized spray is released to the atmosphere. The combined GC-MS and LC-MS system can work either with standard EI or with cold EI via interfacing the flow restriction capillary into a supersonic nozzle forming a supersonic molecular beam of a vibrationally cold sample compound. We found that EI-LC-MS with cold EI has many benefits when compared with standard EI. The EI-LC-MS interface can also serve for flow injection analysis. The performance of the combined system is demonstrated in the analysis of a few sample mixtures by both GC-MS and LC-MS analysis, sequentially without hardware adjustments.
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Affiliation(s)
- Svetlana Tsizin
- School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel
| | | | - Aviv Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel
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13
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Abstract
We report the finding of doubly charged molecular ions in a range of relatively large molecules including hydrocarbons upon their electron ionization as vibrationally cold molecules in supersonic molecular beams (SMB) (also named as Cold EI). Furthermore, we also report the detection by mass spectrometry of triply charged molecular ions in large PAHs such as decacyclene and ovalene upon their cooling in SMB. We found that the relative abundance of doubly charged molecular ions strongly depends on the internal vibrational cooling. While after some vibrational cooling the fragmentation pattern became cooling independent, the relative abundance of the doubly charged molecular ions was noticeably increased upon further cooling via increasing of the cooling make-up gas flow rate. In addition, the relative abundance of the doubly charged molecular ions was strongly increased with the compounds' size, and its electron energy threshold was lower than expected. These observations indicate a new mechanism that involves two separate electron ionization processes in the same compound, most likely with the same electron but at two separate atoms (places) in large molecules, to reduce Coulombic repulsion energy that can lead to fragmentation into two singly charged ions. These findings are shedding new light on electron ionization mass spectra. Accordingly, electron ionization mass spectra are the result of three separate mechanisms with relative magnitudes that depend on the compound size: (a) single electron ionization; (b) double electron ionization; and (c) single electron ionization with subsequent internal excitation by the same ionizing electron in another place.
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Affiliation(s)
| | | | - Uri Keshet
- School of Chemistry , Tel Aviv University , Tel Aviv 6997801 , Israel
| | - Svetlana Tsizin
- School of Chemistry , Tel Aviv University , Tel Aviv 6997801 , Israel
| | - Aviv Amirav
- School of Chemistry , Tel Aviv University , Tel Aviv 6997801 , Israel
- Aviv Analytical Ltd. , 24 Hanagar Street Hod , Hasharon 4527713 , Israel
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Fialkov AB, Lehotay SJ, Amirav A. Less than one minute low-pressure gas chromatography - mass spectrometry. J Chromatogr A 2019; 1612:460691. [PMID: 31759639 DOI: 10.1016/j.chroma.2019.460691] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Revised: 11/05/2019] [Accepted: 11/06/2019] [Indexed: 01/08/2023]
Abstract
Conventional gas chromatography - mass spectrometry (GC-MS) takes 20-40 min per sample, which is undesirably slow in any application if speed can be increased while still meeting analytical needs. In this study, we achieved reasonably good separations with full analysis cycle times of less than 1 min by combining for the first time low-pressure (LP) GC-MS with low thermal mass (LTM) resistive-heating for rapid temperature ramping and cooling of the capillary column. The analytical column is threaded into the LTM thin-walled metal tubing in an instrumental device known as "LTM Fast GC" that is mounted at the top of the gas chromatograph in a detector port. The column inlet and outlet are connected to the GC injector and MS transfer line as usual. For LPGC-MS, a 40 cm, 0.1 mm. i.d. uncoated flow restrictor capillary connected at the injector is coupled with a 2.6 m, 0.25 mm i.d., 0.25 µm film thickness analytical column leading to the MS. Thus, the inlet operates at normal GC pressures, but the analytical column is under vacuum, which increases the optimal helium carrier gas flow velocity thereby increasing speed of full range separations while maintaining acceptable quality of chromatography. This column configuration in LTM-LPGC-MS trades a 64-fold gain in speed of analysis vs. standard GC-MS for a 4-fold loss in chromatographic peak capacity, thereby converting analysis time from minutes into seconds in common applications. For example, jet fuel containing fatty acid methyl esters (akin to biofuel) was separated in 25 s with <1 min full analysis cycle time. An EPA Method 8270 mixture of 76 analytes was also analyzed in <1 min full cycle time by LTM-LPGC-MS. Other examples include very fast analysis of heroin in a street drug powder and elucidation of a new organic synthetic compound. In this report, we describe and discuss the several advantageous and practical features of LTM-LPGC-MS, as well as its trade-offs.
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Affiliation(s)
| | - Steven J Lehotay
- U.S. Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 10938, USA
| | - Aviv Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel; Aviv Analytical Ltd., 24 Hanagar Street, Hod Hasharon 4527713, Israel.
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Potgieter H, de Coning P, Bekker R, Rohwer E, Amirav A. The pre-separation of oxygen containing compounds in oxidised heavy paraffinic fractions and their identification by GC-MS with supersonic molecular beams. J Mass Spectrom 2019; 54:328-341. [PMID: 30720234 DOI: 10.1002/jms.4340] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2018] [Revised: 01/21/2019] [Accepted: 01/28/2019] [Indexed: 06/09/2023]
Abstract
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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Affiliation(s)
- Hein Potgieter
- Operations and Analytics Department, Group Technology R&T, Sasol, Sasolburg, South Africa
| | - Piet de Coning
- Operations and Analytics Department, Group Technology R&T, Sasol, Sasolburg, South Africa
| | - Riaan Bekker
- Operations and Analytics Department, Group Technology R&T, Sasol, Sasolburg, South Africa
| | - Egmont Rohwer
- Department of Chemistry, University of Pretoria, Pretoria, South Africa
| | - Aviv Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv, Israel
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Keshet U, Goldshlag P, Amirav A. Pesticide analysis by pulsed flow modulation GCxGC-MS with Cold EI—an alternative to GC-MS-MS. Anal Bioanal Chem 2017; 410:5507-5519. [DOI: 10.1007/s00216-017-0757-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Revised: 10/29/2017] [Accepted: 11/08/2017] [Indexed: 10/18/2022]
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Tsizin S, Seemann B, Alon T, Amirav A. Second hydrogen atom abstraction by molecular ions. J Mass Spectrom 2017; 52:638-642. [PMID: 28685904 DOI: 10.1002/jms.3966] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Revised: 06/25/2017] [Accepted: 07/03/2017] [Indexed: 06/07/2023]
Abstract
We report the observation of a new physical phenomenon of the addition of 2 hydrogen atoms to molecular ions thus forming [M + 2H]+ ions. We demonstrate such second hydrogen atom abstraction onto the molecular ions of pentaerythritol and trinitrotoluene (TNT). We used both gas chromatography mass spectrometry (GC-MS) with supersonic molecular beam (SMB) with methanol added into its make-up gas and electron ionization (EI) liquid chromatography mass spectrometry (LC-MS) with SMB with methanol as the LC solvent. We found that the formation of methanol clusters resulted upon EI in the formation of dominant protonated pentaerythritol ion at m/z = 137 plus about 70% relative abundance of pentaerythritol molecular ion with 2 additional hydrogen atoms at m/z = 138 which is well above the 5.7% natural C13 isotope abundance of protonated pentaerythritol. Similarly, we found an abundant protonated TNT ion at m/z = 228 and a similar abundance of TNT molecular ion with 2 additional hydrogen atoms at m/z = 229. Upon the use of deuterated methanol (CD3 OD) as the solvent, we observed an abundant m/z = 231 (M + 2D)+ of TNT with 2 deuterium atoms. We found such abundant second hydrogen atom abstraction with butylglycolate and at low abundances in dioctylphthalate, Vitamin K3, phenazine, and RDX. At this time, we are unable to report the magnitude and frequency of occurrence of this phenomenon in standard electrospray LC-MS. This observation could have important implications on the provision of elemental formula from mass spectra that are involved with protonated molecules. Accordingly, while accurate mass measurements can serve for the generation of elemental formula, their further support and improvement via isotope abundance analysis are questionable. Consequently, if a given compound can be analyzed by both GC-MS and LC-MS, its GC-MS analysis can be superior for the provision of accurate elemental formulae if its EI mass spectrum exhibits abundant molecular ions such as with GC-MS with SMB (also known as cold EI).
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Affiliation(s)
- Svetlana Tsizin
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
| | - Boaz Seemann
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
| | - Tal Alon
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
| | - Aviv Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
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Keshet U, Alon T, Fialkov AB, Amirav A. Open Probe fast GC-MS - combining ambient sampling ultra-fast separation and in-vacuum ionization for real-time analysis. J Mass Spectrom 2017; 52:417-426. [PMID: 28455844 DOI: 10.1002/jms.3941] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Revised: 04/02/2017] [Accepted: 04/25/2017] [Indexed: 06/07/2023]
Abstract
An Open Probe inlet was combined with a low thermal mass ultra-fast gas chromatograph (GC), in-vacuum electron ionization ion source and a mass spectrometer (MS) of GC-MS for obtaining real-time analysis with separation. The Open Probe enables ambient sampling via sample vaporization in an oven that is open to room air, and the ultra-fast GC provides ~30-s separation, while if no separation is required, it can act as a transfer line with 2 to 3-s sample transfer time. Sample analysis is as simple as touching the sample, pushing the sample holder into the Open Probe oven and obtaining the results in 30 s. The Open Probe fast GC was mounted on a standard Agilent 7890 GC that was coupled with an Agilent 5977A MS. Open Probe fast GC-MS provides real-time analysis combined with GC separation and library identification, and it uses the low-cost MS of GC-MS. The operation of Open Probe fast GC-MS is demonstrated in the 30-s separation and 50-s full analysis cycle time of tetrahydrocannabinol and cannabinol in Cannabis flower, sub 1-min analysis of trace trinitrotoluene transferred from a finger onto a glass surface, vitamin E in canola oil, sterols in olive oil, polybrominated flame retardants in plastics, alprazolam in Xanax drug pill and free fatty acids and cholesterol in human blood. The extrapolated limit of detection for pyrene is <1 fg, but the concentration is too high and the software noise calculation is untrustworthy. The broad range of compounds amenable for analysis is demonstrated in the analysis of reserpine. The possible use with alternate standard GC-MS and Open Probe fast GC-MS is demonstrated in the analysis of heroin in its street drug powder. The use of Open Probe with the fast GC acting as a transfer line is demonstrated in <10-s analysis without separation of ibuprofen and estradiol. Copyright © 2017 John Wiley & Sons, Ltd.
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Affiliation(s)
- U Keshet
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
| | - T Alon
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
| | - A B Fialkov
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
| | - A Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
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Alon T, Amirav A. How enhanced molecular ions in Cold EI improve compound identification by the NIST library. Rapid Commun Mass Spectrom 2015; 29:2287-92. [PMID: 26522322 DOI: 10.1002/rcm.7392] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Revised: 09/06/2015] [Accepted: 09/08/2015] [Indexed: 05/05/2023]
Abstract
RATIONALE Library-based compound identification with electron ionization (EI) mass spectrometry (MS) is a well-established identification method which provides the names and structures of sample compounds up to the isomer level. The library (such as NIST) search algorithm compares different EI mass spectra in the library's database with the measured EI mass spectrum, assigning each of them a similarity score called 'Match' and an overall identification probability. Cold EI, electron ionization of vibrationally cold molecules in supersonic molecular beams, provides mass spectra with all the standard EI fragment ions combined with enhanced Molecular Ions and high-mass fragments. As a result, Cold EI mass spectra differ from those provided by standard EI and tend to yield lower matching scores. However, in most cases, library identification actually improves with Cold EI, as library identification probabilities for the correct library mass spectra increase, despite the lower matching factors. METHODS This research examined the way that enhanced molecular ion abundances affect library identification probability and the way that Cold EI mass spectra, which include enhanced molecular ions and high-mass fragment ions, typically improve library identification results. It involved several computer simulations, which incrementally modified the relative abundances of the various ions and analyzed the resulting mass spectra. RESULTS The simulation results support previous measurements, showing that while enhanced molecular ion and high-mass fragment ions lower the matching factor of the correct library compound, the matching factors of the incorrect library candidates are lowered even more, resulting in a rise in the identification probability for the correct compound. CONCLUSIONS This behavior which was previously observed by analyzing Cold EI mass spectra can be explained by the fact that high-mass ions, and especially the molecular ion, characterize a compound more than low-mass ions and therefore carries more weight in library search identification algorithms. These ions are uniquely abundant in Cold EI, which therefore enables enhanced compound characterization along with improved NIST library based identification.
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Affiliation(s)
- Tal Alon
- School of Chemistry, Tel Aviv University, Tel Aviv, 6997801, Israel
- Afeka Academic College of Engineering, Tel Aviv, 6998812, Israel
| | - Aviv Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv, 6997801, Israel
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Amirav A, Keshet U, Danon A. Soft Cold EI - approaching molecular ion only with electron ionization. Rapid Commun Mass Spectrom 2015; 29:1954-1960. [PMID: 26443393 DOI: 10.1002/rcm.7305] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2015] [Revised: 08/02/2015] [Accepted: 08/06/2015] [Indexed: 06/05/2023]
Abstract
RATIONALE Cold EI is defined as electron ionization of cold molecules in supersonic molecular beams (SMB). Gas chromatography/mass spectrometry (GC/MS) with Cold EI provides informative mass spectra, which combine the usual library-searchable EI fragment ions with enhanced molecular ions for improved library-based identification probabilities. However, in some cases, such as in the analysis of complex petrochemical matrices, a soft ionization method that provides only molecular ions is desirable. METHODS GC/MS with Cold EI was used with a fly-through ion source at selected electron energies, including at low electron energies, in an attempt to observe molecular ions alone. RESULTS We explored low electron energy Cold EI and found that once the sample compound is cooled by the supersonic expansion it can be reheated via reflected scattered helium atoms near the skimmer. Furthermore, once a labile molecular ion is formed it can undergo undesirable collision-induced dissociation (CID) in the same way as in tandem mass spectrometry (MS/MS), and the magnitude of such CID can be significant for labile molecular ions such as those of hydrocarbons. In order to reduce these adverse effects we reduced the helium pressure at the ion source and MS vacuum chamber by increasing the nozzle-skimmer distance. Cold EI at low electron energies was explored with a squalane isomer (C30 H62 ) and with n-C24 H50 . CONCLUSIONS It was found that an increased nozzle-skimmer distance resulted in a noticeable increase in the abundance ratio of molecular ions to low mass fragment ions. Consequently, Cold EI at low electron energies and a large nozzle-skimmer distance converts EI into Soft Cold EI while further approaching the ideal of a molecular ion only ionization method.
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Affiliation(s)
- Aviv Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
| | - Uri Keshet
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
| | - Albert Danon
- Nuclear Research Center Negev, P.O. Box 9001, Beer Sheva, Israel
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Seemann B, Alon T, Tsizin S, Fialkov AB, Amirav A. Electron ionization LC-MS with supersonic molecular beams--the new concept, benefits and applications. J Mass Spectrom 2015; 50:1252-63. [PMID: 26505770 DOI: 10.1002/jms.3695] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2015] [Revised: 08/19/2015] [Accepted: 08/20/2015] [Indexed: 05/28/2023]
Abstract
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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Affiliation(s)
- Boaz Seemann
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
| | - Tal Alon
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
| | - Svetlana Tsizin
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
| | | | - Aviv Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv, 69978, Israel
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23
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Amirav A, Gordin A, Hagooly Y, Rozen S, Belgorodsky B, Seemann B, Marom H, Gozin M, Fialkov AB. Measurement and optimization of organic chemical reaction yields by GC–MS with supersonic molecular beams. Tetrahedron 2012. [DOI: 10.1016/j.tet.2012.05.031] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Fialkov AB, Morag M, Amirav A. A low thermal mass fast gas chromatograph and its implementation in fast gas chromatography mass spectrometry with supersonic molecular beams. J Chromatogr A 2011; 1218:9375-83. [DOI: 10.1016/j.chroma.2011.10.053] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2011] [Revised: 10/18/2011] [Accepted: 10/20/2011] [Indexed: 10/15/2022]
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26
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Affiliation(s)
- Marina Poliak
- School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel
| | - Alexander Gordin
- School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel
| | - Aviv Amirav
- School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel
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Alon T, Amirav A. Isotope abundance analysis for improved sample identification with tandem mass spectrometry. Rapid Commun Mass Spectrom 2009; 23:3668-3672. [PMID: 19899190 DOI: 10.1002/rcm.4306] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Tandem mass spectrometry (MS/MS) is widely used for trace level sample analysis in complex mixtures. However, sample identification in MS/MS is challenging and not as trustworthy as with electron ionization (EI) mass spectral libraries. This paper presents a novel method for the combination of isotope abundance analysis (IAA) and EI-MS/MS for improved sample identification even at trace level in complex matrices. Accordingly, the first quadrupole is scanned in a narrow range around the molecular ion group of isotopomers such as M+, [M+1]+ and [M+2]+, Q2 serves for collision-induced dissociation to produce product ions while Q3 transfers the major sample product ions with low resolution, thus encompassing and uniformly transmitting all the product ion isotopomers. IAA can then be used to derive elemental formula information from the cleansed experimental data. IAA-MS/MS was experimentally tested with perfluorotributylamine and a very good matching factor of 995 (out of 1000) was obtained for IAA on m/z 502, 503 and 504 (fragment ion isotopomers) while Q3 transmitted the m/z 264 product ion with a mass window of 6 m/z units. The IAA-MS/MS method was further tested with the pesticide diazinon on its molecular ions m/z 304, 305 and 306 while Q3 was locked on its m/z 179 product ion with a mass window of 6 m/z units. Again, very good matching factors were obtained, even for 40 pg diazinon on-column during its GC/MS analysis (match = 981). IAA-MS/MS combines the traditional benefits of MS/MS in the removal of matrix interferences with the IAA power of elemental analysis.
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Affiliation(s)
- Tal Alon
- School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel
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Brondz I, Fialkov AB, Amirav A. Erratum to “Analysis of quinocide in unprocessed primaquine diphosphate and primaquine diphosphate tablets using gas chromatography–mass spectrometry with supersonic molecular beams” [J. Chromatogr. A 1216 (2009) 824–829]. J Chromatogr A 2009. [DOI: 10.1016/j.chroma.2009.01.049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Brondz I, Fialkov AB, Amirav A. Analysis of quinocide in unprocessed primaquine diphosphate and primaquine diphosphate tablets using gas chromatography-mass spectrometry with supersonic molecular beams. J Chromatogr A 2009; 1216:824-9. [PMID: 19108846 DOI: 10.1016/j.chroma.2008.11.043] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2008] [Revised: 11/11/2008] [Accepted: 11/17/2008] [Indexed: 11/18/2022]
Abstract
Malaria is one of the most widespread and deadly diseases on the planet. Every year, about 500 million new cases are diagnosed, and the annual death toll is about 3 million. Primaquine has strong antiparasitic effects against gametocytes and can therefore prevent the spread of the parasite from treated patients to mosquitoes. It is also used in radical cures and prevents relapse. Consequently, primaquine is an often-used drug. In this study the separation of unprocessed primaquine from the contaminant quinocide based on gas chromatography-mass spectrometry with supersonic molecular beam (SMB) is presented and 7.5 mg primaquine diphosphate tablets were analyzed. We present a novel method for fast determination of quinocide which is an isomer of primaquine as the main contaminant in unprocessed primaquine and in its medical form as tablets by gas chromatography-mass spectrometry with SMB (also named supersonic GC-MS). Supersonic GC-MS provides enhanced molecular ion without any ion source related peak tailing plus extended range of compounds amenable for GC-MS analysis. In addition, major isomer mass spectral effects were revealed in the mass spectra of primaquine and quinocide which facilitated the unambiguous identification of quinocide in primaquine tablets. Fast GC-MS analysis is demonstrated with less then 2 min elution time of the drug and its main contaminants.
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Affiliation(s)
- Ilia Brondz
- Department of Biology, University of Oslo, Oslo, Norway.
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Lehotay SJ, Mastovska K, Amirav A, Fialkov AB, Martos PA, Kok AD, Fernández-Alba AR. Identification and confirmation of chemical residues in food by chromatography-mass spectrometry and other techniques. Trends Analyt Chem 2008. [DOI: 10.1016/j.trac.2008.10.004] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Poliak M, Fialkov AB, Amirav A. Pulsed flow modulation two-dimensional comprehensive gas chromatography–tandem mass spectrometry with supersonic molecular beams. J Chromatogr A 2008; 1210:108-14. [DOI: 10.1016/j.chroma.2008.09.039] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2008] [Revised: 09/02/2008] [Accepted: 09/10/2008] [Indexed: 10/21/2022]
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Gordin A, Fialkov AB, Amirav A. Classical electron ionization mass spectra in gas chromatography/mass spectrometry with supersonic molecular beams. Rapid Commun Mass Spectrom 2008; 22:2660-2666. [PMID: 18666200 DOI: 10.1002/rcm.3654] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
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.
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Affiliation(s)
- Alexander Gordin
- School of Chemistry, Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
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Poliak M, Kochman M, Amirav A. Pulsed flow modulation comprehensive two-dimensional gas chromatography. J Chromatogr A 2008; 1186:189-95. [PMID: 17915235 DOI: 10.1016/j.chroma.2007.09.030] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2007] [Revised: 09/10/2007] [Accepted: 09/14/2007] [Indexed: 11/28/2022]
Abstract
Pulsed flow modulation (PFM) is based on higher flow rate time compression of the first GC column effluent, which prior to the injection into the second column is stored for a few seconds in a standard fused silica wide bore transfer line. We constructed the PFM device with two standard 1/16 in. brass compression fittings with the insertion of the two columns inside the wide bore 0.53 mm i.d. fused silica storage transfer line for the elimination of dead volumes. This simple arrangement provides a combination of flexibility in the length of the sample storage transfer line hence comprehensive two-dimensional gas chromatography (GC x GC) cycle time, inert sample path and full elimination of cooling gas consumption. A record short second column injection time of 20 ms is demonstrated. Practical injection times are the sample collection time (such as 4s) divided by the second to first column flow rate ratio (such as 20/0.7), which is typically around 150 ms. Due to the low cost of the device it can also be considered for use with non comprehensive time segmented GC x GC to remove a few accidental coelutions. PFM-GCxGC excels with high second column capacity due to the use of 0.32 mm i.d. columns with high flow rates as the second dimension GC x GC column. As a result, PFM-GCxGC can have up to two orders of magnitude higher second column sample capacity and linear dynamic range for improved reduction of adverse matrix interference effects due to column overloading.
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Affiliation(s)
- Marina Poliak
- School of Chemistry, Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
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Abstract
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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Affiliation(s)
- Aviv Amirav
- School of Chemistry, Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
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Kochman M, Gordin A, Alon T, Amirav A. Flow modulation comprehensive two-dimensional gas chromatography–mass spectrometry with a supersonic molecular beam. J Chromatogr A 2006; 1129:95-104. [PMID: 16834991 DOI: 10.1016/j.chroma.2006.06.079] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2006] [Revised: 06/20/2006] [Accepted: 06/23/2006] [Indexed: 10/24/2022]
Abstract
A new approach of flow modulation comprehensive two-dimensional gas chromatography-mass spectrometry (GC x GC-MS) with supersonic molecular beam (SMB) and a quadrupole mass analyzer is presented. Flow modulation uniquely enables GC x GC-MS to be achieved even with the limited scan speed of quadrupole MS, and its 20 ml/min column flow rate is handled, splitless, by the SMB interface. Flow modulation GC x GC-SMB-MS shares all the major benefits of GC x GC and combines them with GC-MS including: (a) increased GC separation capability; (b) improved sensitivity via narrower GC peaks; (c) improved sensitivity through reduced matrix interference and chemical noise; (d) polarity and functional group sample information via the order of elution from the second polar column. In addition, GC x GC-SMB-MS is uniquely characterized by the features of GC-MS with SMB of enhanced and trustworthy molecular ion plus isotope abundance analysis (IAA) for improved sample identification and fast fly-through ion source response time. The combination of flow modulation GC x GC with GC-MS with SMB (supersonic GC-MS) was explored with complex matrices such as diesel fuel analysis and pesticide analysis in agricultural products.
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Affiliation(s)
- Maya Kochman
- School of Chemistry, Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
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Jánská M, Lehotay SJ, Mastovská K, Hajslová J, Alon T, Amirav A. A simple and inexpensive “solvent in silicone tube extraction” approach and its evaluation in the gas chromatographic analysis of pesticides in fruits and vegetables. J Sep Sci 2006; 29:66-80. [PMID: 16485711 DOI: 10.1002/jssc.200500237] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A novel, simple, and inexpensive approach to sorptive extraction, which we call solvent in silicone tube extraction (SiSTEx), was applied to pesticide residue analysis and its effectiveness and efficiency were evaluated. In SiSTEx, which is a form of open tubular sorptive extraction, a piece of silicone tubing (4 cm long, 1.47 mm ID, 1.96 mm OD in this study) is attached to the cap of a 20 mL glass vial that contains the aqueous sample. The tubing is plugged at the end dangling in the sample solution, and MeCN (e.g., 40 microL) added by syringe to the inner tube volume through a septum in the cap. A stir-bar is used to mix the sample for a certain time (e.g., 60 min), which allows chemicals to partition into the tubing where they diffuse across the silicone and partition into the MeCN. The final MeCN extract is then analyzed for the concentrated analytes. In this study, the SiSTEx approach was evaluated for the analysis of organophosphorus (OP) and organochlorine (OC) pesticides in fruits and vegetables using GC/pulsed flame photometric (PFPD) and halogen specific (XSD) detectors for analysis. The produced samples were initially extracted by a rapid MeCN procedure, and 5 mL of the initial extract was diluted four-fold with water to undergo sorptive extraction for 60 min. The final extract was analyzed by GC/PFPD + XSD for 14 OP and 22 OC pesticides. This simple approach was able to detect 26 of the 36 pesticides at 10 ng/g or less original equivalent sample concentration with average reproducibility of 11% RSD. For those 26 pesticides, a 44-fold lower detection limit on average was achieved in matrix extracts using SiSTEx despite the four-fold dilution with water.
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Affiliation(s)
- Marie Jánská
- Department of Food Chemistry and Analysis, Institute of Chemical Technology, Prague, Czech Republic
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Alon T, Amirav A. Isotope abundance analysis methods and software for improved sample identification with supersonic gas chromatography/mass spectrometry. Rapid Commun Mass Spectrom 2006; 20:2579-88. [PMID: 16897787 DOI: 10.1002/rcm.2637] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
We present newly developed isotope abundance analysis (IAA) methods and software which are used to derive elemental formula information from experimental mass spectral data of molecular ion isotopomeric abundances. The software, using a novel method, can also be used to automatically confirm or reject NIST library search results, thereby significantly improving the confidence level in sample identifications. In the case of IAA confirmation of the NIST library results, sample identification is unambiguous, since the confirmation is achieved by two independent sets of data and analytical methods. In the case of a rejection, such as when the molecule is not included in the library's databases, the IAA software independently provides a list of elemental formulae with declining order of matching to the isotopomeric experimental data, in a similar way to accurate mass measurements with costly instruments. IAA is ideally applicable to gas chromatography/mass spectrometry (GC/MS) (and liquid chromatography/electron ionization mass spectrometry (LC/EI-MS)) with a supersonic molecular beam (SMB) since it requires a trustworthy and highly abundant true molecular ion that is unique to the SMB-MS systems, plus the absence of self chemical ionization and vacuum background noise, again unique features of GC/SMB-MS. The various features of the IAA methods and software are described, their performance is demonstrated with the analysis of experimental GC-SMB-MS data and the IAA concept is compared with accurate mass alternatives. The combination of IAA and GC/SMB-MS is believed to be superior to accurate mass GC/MS in view of the general availability of trustworthy molecular ions for an extended range of compounds.
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Affiliation(s)
- Tal Alon
- School of Chemistry, Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
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Abstract
We present a spray based-method for the formation and production of semiconductor nanocrystals that provides an attractive alternative to the commonly used epitaxial and colloidal procedures. According to this spray-based method, mainly thermospray, solutions of semiconductor salts are first sprayed into monodispersed droplets, which subsequently become solid nanocrystals by solvent evaporation. A semiconductor nanocrystal is produced from a single spray droplet upon the full vaporization of the solvent. The average diameter and size distribution of the final nanocrystals are controlled and determined by the solute concentration of the sprayed solution and by the droplet size, hence by the spray production parameters. The spray-produced nanocrystals are collected on any selected solid support. Representative results, shown in this letter, reveal the formation of CdS nanocrystals in the size range of 3 to 6 nanometers and with a size distribution of as low as five percent. A further structural analysis of these nanocrystals showed that they were formed in the zinc blend phase with a high degree of crystallinity.
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Fialkov AB, Amirav A. Identification of novel synthetic organic compounds with supersonic gas chromatography-mass spectrometry. J Chromatogr A 2004; 1058:233-42. [PMID: 15595673] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/01/2023]
Abstract
Several novel synthetic organic compounds were successfully analyzed with a unique type of GC-MS titled Supersonic GC-MS following a failure in their analysis with standard GC-MS. Supersonic GC-MS is based on interfacing GC and MS with a supersonic molecular beam (SMB) and on electron ionization of sample compounds as vibrationally cold molecules while in the SMB, or by cluster chemical ionization. The analyses of novel synthetic organic compounds significantly benefited from the extended range of compounds amenable to analyses with the Supersonic GC-MS. The Supersonic GC-MS enabled the analysis of thermally labile compounds that usually degrade in the GC injector, column and/or ion source. Due to the high carrier gas flow rate at the injector liner and column these compounds eluted without degradation at significantly lower elution temperatures and the use of fly-through EI ion source eliminated any sample degradation at the ion source. The cold EI feature of providing trustworthy enhanced molecular ion (M+), complemented by its optional further confirmation with cluster CI was highly valued by the synthetic organic chemists that were served by the Supersonic GC-MS. Furthermore, the provision of extended mass spectral structural, isomer and isotope information combined with short (a few minutes) GC-MS analysis times also proved beneficial for the analysis of unknown synthetic organic compounds. As a result, the synthetic organic chemists were provided with both qualitative and quantitative data on the composition of their synthetic mixture, and could better follow the path of their synthetic chemistry. Ten cases of such analyses are demonstrated in figures and discussed.
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Affiliation(s)
- Alexander B Fialkov
- School of Chemistry, Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
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Abstract
A setup combining laser desorption of nonvolatile molecules and their aerodynamic acceleration in a supersonic molecular beam followed by hyperthermal surface ionization in a reflectron time-of-flight mass spectrometer is described. While laser desorption performs the intact transfer of the analyte molecules into the gas phase, hyperthermal surface ionization opens up the possibility to efficiently ionize even larger molecules with a small and potentially controlled degree of fragmentation. Being an ionization technique, which is particularly effective for aromatic and heterocyclic compounds, the selectivity can further be increased by tuning the kinetic energy to which the molecules are accelerated in the supersonic beam. The results obtained for several polycyclic aromatic hydrocarbons and biochemical substances show that sufficient acceleration can be achieved even for molecules with a molecular weight above 5000 amu and that HSI preserves its advantageous features even for thermally labile large molecules such as insulin.
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Affiliation(s)
- Christian Weickhardt
- Department of Computer Science, Mathematics and Natural Sciences, Leipzig University of Applied Sciences, Trufanow Strasse 6, 04105 Leipzig, Germany.
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Abstract
Gas chromatography-mass spectrometry (GC-MS) suffers from a major limitation in that an expanding number of thermally labile or low volatility compounds of interest are not amenable for analysis. We found that the elution temperatures of compounds from GC can be significantly lowered by reducing the column length, increasing the carrier gas flow rate, reducing the capillary column film thickness and lowering the temperature programming rate. Pyrene is eluted at 287 degrees C in standard GC-MS with a 30 m x 0.25 mm I.D. column with 1-microm DB5ms film and 1-ml/min He column flow rate. In contrast, pyrene is eluted at 79 degrees C in our "Supersonic GC-MS" system using a 1 m x 0.25 mm I.D. column with 0.1-microm DB5ms film and 100-ml/min He column flow rate. A simple model has been invoked to explain the significantly (up to 208 degrees C) lower elution temperatures observed. According to this model, every halving of the temperature programming rate, or number of separation plates (either through increased flow rate or due to reduced column length), results in approximately 20 degrees C lower elution temperature. These considerably lower elution temperatures enable the analysis of an extended range of thermally labile and low volatility compounds, that otherwise could not be analyzed by standard GC-MS. We demonstrate the analysis of large polycyclic aromatic hydrocarbons (PAHs) such as decacyclene with ten fused rings, well above the current GC limit of PAHs with six rings. Even a metalloporphirin such as magnesiumoctaethylporphin was easily analyzed with elution temperatures below 300 degrees C. Furthermore, a range of thermally labile compounds were analyzed including carbamates such as methomyl, aldicarb, aldicarbsulfone and oxamyl, explosives such as pentaerythritol tetranitrate, Tetryl and HMX, and drugs such as reserpine (608 a.m.u.). Supersonic GC-MS was used, based on the coupling of a supersonic molecular beam (SMB) inlet and ion sources with a bench-top Agilent 6890 GC plus 5972 MSD. The Supersonic GC-MS provides enhanced molecular ion without any ion source related peak tailing. Thus, the lower GC separation power involved in the analysis of thermally labile and low volatility compounds is compensated by increased separation power of the MS gained from the enhanced molecular ion. Several implications of these findings are discussed, including our conclusion that slower chromatography leads to better analysis of thermally labile compounds.
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Affiliation(s)
- Alexander B Fialkov
- School of Chemistry, Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978 Israel
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Fialkov AB, Amirav A. Cluster chemical ionization for improved confidence level in sample identification by gas chromatography/mass spectrometry. Rapid Commun Mass Spectrom 2003; 17:1326-1338. [PMID: 12811756 DOI: 10.1002/rcm.1057] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Upon the supersonic expansion of helium mixed with vapor from an organic solvent (e.g. methanol), various clusters of the solvent with the sample molecules can be formed. As a result of 70 eV electron ionization of these clusters, cluster chemical ionization (cluster CI) mass spectra are obtained. These spectra are characterized by the combination of EI mass spectra of vibrationally cold molecules in the supersonic molecular beam (cold EI) with CI-like appearance of abundant protonated molecules, together with satellite peaks corresponding to protonated or non-protonated clusters of sample compounds with 1-3 solvent molecules. Like CI, cluster CI preferably occurs for polar compounds with high proton affinity. However, in contrast to conventional CI, for non-polar compounds or those with reduced proton affinity the cluster CI mass spectrum converges to that of cold EI. The appearance of a protonated molecule and its solvent cluster peaks, plus the lack of protonation and cluster satellites for prominent EI fragments, enable the unambiguous identification of the molecular ion. In turn, the insertion of the proper molecular ion into the NIST library search of the cold EI mass spectra eliminates those candidates with incorrect molecular mass and thus significantly increases the confidence level in sample identification. Furthermore, molecular mass identification is of prime importance for the analysis of unknown compounds that are absent in the library. Examples are given with emphasis on the cluster CI analysis of carbamate pesticides, high explosives and unknown samples, to demonstrate the usefulness of Supersonic GC/MS (GC/MS with supersonic molecular beam) in the analysis of these thermally labile compounds. Cluster CI is shown to be a practical ionization method, due to its ease-of-use and fast instrumental conversion between EI and cluster CI, which involves the opening of only one valve located at the make-up gas path. The ease-of-use of cluster CI is analogous to that of liquid CI in ion traps with internal ionization, and is in marked contrast to that of CI with most other standard GC/MS systems that require a change of the ion source.
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Affiliation(s)
- Alexander B Fialkov
- School of Chemistry, Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
| | - Aviv Amirav
- School of Chemistry, Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
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Amirav A, Sonnenschein M, Jortner J. Statistical-limit line broadening in the S2 state of phenanthrene in supersonic jets. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j150667a027] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Sonnenschein M, Amirav A, Jortner J. Absolute fluorescence quantum yields of large molecules in supersonic expansions. ACTA ACUST UNITED AC 2002. [DOI: 10.1021/j150663a005] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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