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Weber M, Wolf JC, Haisch C. Effect of Dopants and Gas-Phase Composition on Ionization Behavior and Efficiency in Dielectric Barrier Discharge Ionization. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2023; 34:538-549. [PMID: 36827232 DOI: 10.1021/jasms.2c00279] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Cold plasma-based ionization techniques allow for soft ionization of a wide variety of chemical compounds. In this chemical ionization mechanism, the atmosphere plays a crucial role in ionization. Knowing its influence is critical for the optimization of analysis conditions and interpretation of resulting spectra. This study uses soft ionization by chemical reaction in transfer (SICRIT), a variant of dielectric barrier discharge ionization (DBDI), that allows for a controlled atmosphere to investigate atmosphere and dopant effects. The influence of eight makeup gas compositions (dry nitrogen, room air, and nitrogen-enriched with either water, HCl, MeOH, hexane, NH3, and fluorobenzene) on the ionization with SICRIT was investigated. Fifteen compound classes, comprising alkanes, polyaromatic hydrocarbons (PAHs), terpenes, oxygen-containing terpenes, alkylphenols, chlorophenols, nitrophenols, trialkylamines, triazines, phthalates with or without ether groups, aldehydes, ketones, fatty acid methyl esters (FAMEs), and polyoxy-methylene ethers (OMEs) were measured via gas chromatography SICRIT high-resolution mass spectrometry (GC-SICRIT-HRMS). The different atmospheres were compared in terms of generated ions, ion intensities and fragmentation during ionization. Measurements of reactant ions were performed for a better understanding of the underlying mechanisms. All 15 compound classes were mostly softly ionized. For most compound classes and atmospheres, protonation is the dominant ionization mode. The highest number of compounds ionized via protonation was observed in dry nitrogen, followed by room air and humid nitrogen. The study should work as a guideline for the choice of atmosphere for specific compound classes and the interpretation of spectra generated under a specific atmosphere.
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Affiliation(s)
- Markus Weber
- Chair of Analytical Chemistry and Water Chemistry, Technical University of Munich, 85748 Garching, Germany
- Plasmion GmbH, 86167 Augsburg, Germany
| | | | - Christoph Haisch
- Chair of Analytical Chemistry and Water Chemistry, Technical University of Munich, 85748 Garching, Germany
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2
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Zhang D, Latif M, Gamez G. Instantaneous Differentiation of Functional Isomers via Reactive Flowing Atmospheric Pressure Afterglow Mass Spectrometry. Anal Chem 2021; 93:9986-9994. [PMID: 34251188 DOI: 10.1021/acs.analchem.0c04867] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Ambient mass spectrometry (AMS) allows direct desorption and ionization of analytes in real time with minimal-to-no sample preparation. However, it may present inadequate capabilities for differentiating isomers. Here, a reactive flowing atmospheric-pressure afterglow (reactive-FAPA) AMS source is developed for rapid isomer differentiation by derivatization of analytes in real time. The effects of the reactive-FAPA operating conditions on the reagent and product ions were studied and optimized for highly volatile and non-volatile model compounds with different carbonyl functional groups. In addition, two functional isomers of valproic acid (VPA) metabolites, 4-ene VPA and γ-valprolactone, are successfully differentiated for the first time by incorporating methylamine (MA) reagent vapor into the plasma effluent used for desorption/ionization. Reactive-FAPAMS for 4-ene VPA shows only detectable peaks of the protonated acylation product [M + MA-H2O + H]+, while for γ-valprolactone, it shows detectable peaks for both protonated acylation product [M + MA-H2O + H]+ and protonated intermediate [M + MA + H]+. A method for quantitative characterization of mixtures of 4-ene VPA and γ-valprolactone is also developed and validated. In addition, reactive-FAPAMS also shows better detection sensitivity compared to nonreactive-FAPAMS for some larger analyte types, such as UV filters and steroids. The limit of detection (LOD) of pregnenolone acetate in reactive-FAPAMS is 310 ng/mL, which is about 10 times better than its LOD in nonreactive-FAPA.
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Affiliation(s)
- Dong Zhang
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, United States
| | - Mohsen Latif
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, United States
| | - Gerardo Gamez
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, United States
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3
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Zhang X, Mell A, Li F, Thaysen C, Musselman B, Tice J, Vukovic D, Rochman C, Helm PA, Jobst KJ. Rapid fingerprinting of source and environmental microplastics using direct analysis in real time-high resolution mass spectrometry. Anal Chim Acta 2019; 1100:107-117. [PMID: 31987130 DOI: 10.1016/j.aca.2019.12.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Revised: 11/29/2019] [Accepted: 12/01/2019] [Indexed: 11/26/2022]
Abstract
Microplastics are ubiquitous in the aquatic and terrestrial environment. To prevent further contamination, methods to determine their sources are needed. Techniques to quantify and characterize microplastics in the environment are still evolving for polymers and the additives and leachable substances embedded therein, which constitute the "chemical fingerprint" of an environmental microplastic. There is a critical need for analytical methods that yield such diagnostic information on environmental microplastics that enables identification of their composition and sources of pollution. This study reports on a novel approach for rapid fingerprinting of environmental microplastics and the screening of additives using Direct Analysis in Real Time (DART)-high resolution mass spectrometry. A variety of plastic samples were investigated, including virgin pre-production pellets, microbeads from personal care products, microplastics found in the aquatic environment, and synthetic fibers. The resulting mass spectra display ∼10,000 discrete peaks, corresponding to plastic additives released by thermal desorption and polymer degradation products generated by pyrolysis. These were used to characterize differences among plastic types, microplastic source materials, and environmental samples. Multivariate statistics and elemental composition analysis approaches were applied to analyze fingerprints from the mass spectra. This promising analytical approach is sensitive, (potentially) high-throughput, and can aid in the elucidation of possible sources of microplastics and perhaps eventually to the analysis of bulk environmental samples for plastics.
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Affiliation(s)
- Xianming Zhang
- Ontario Ministry of the Environment, Conservation and Parks, Toronto, Ontario, M9P 3V6, Canada.
| | - Alicia Mell
- Ontario Ministry of the Environment, Conservation and Parks, Toronto, Ontario, M9P 3V6, Canada
| | - Frederick Li
- IonSense Inc. Saugus, Massachusetts, 01906, USA.
| | - Clara Thaysen
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, M5S 3H6, Canada.
| | | | - Joseph Tice
- IonSense Inc. Saugus, Massachusetts, 01906, USA
| | | | - Chelsea Rochman
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, M5S 3H6, Canada.
| | - Paul A Helm
- Ontario Ministry of the Environment, Conservation and Parks, Toronto, Ontario, M9P 3V6, Canada.
| | - Karl J Jobst
- Ontario Ministry of the Environment, Conservation and Parks, Toronto, Ontario, M9P 3V6, Canada; Department of Chemistry, Memorial University of Newfoundland, St. John's, NL A1B 3X7, Canada.
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4
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Rapid volatiles fingerprinting by dopant-assisted positive photoionization ion mobility spectrometry for discrimination and characterization of Green Tea aromas. Talanta 2019; 191:39-45. [DOI: 10.1016/j.talanta.2018.08.039] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Revised: 08/03/2018] [Accepted: 08/12/2018] [Indexed: 11/23/2022]
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5
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Saboohi S, Griesser HJ, Coad BR, Short RD, Michelmore A. Promiscuous hydrogen in polymerising plasmas. Phys Chem Chem Phys 2018; 20:7033-7042. [PMID: 29473064 DOI: 10.1039/c7cp08166a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Historically, there have been two opposing views regarding deposition mechanisms in plasma polymerisation, radical growth and direct ion deposition, with neither being able to fully explain the chemistry of the resultant coating. Deposition rate and film chemistry are dependent on the chemistry of the plasma phase and thus the activation mechanisms of species in the plasma are critical to understanding the relative contributions of various chemical and physical routes to plasma polymer formation. In this study, we investigate the roles that hydrogen plays in activating and deactivating reactive plasma species. Ethyl trimethylacetate (ETMA) is used as a representative organic precursor, and additional hydrogen is added to the plasma in the form of water and deuterium oxide. Optical emission spectroscopy confirms that atomic hydrogen is abundant in the plasma. Comparison of the plasma phase mass spectra of ETMA/H2O and ETMA/D2O reveals that (1) proton transfer from hydronium is a common route to charging precursors in plasma, and (2) hydrogen abstraction (activation) and recombination (deactivation) processes are much more dynamic in the plasma than previously thought. Consideration of the roles of hydrogen in plasma chemistry may then provide a more comprehensive view of deposition processes and bridge the divide between the two disparate schools of thought.
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Affiliation(s)
- Solmaz Saboohi
- Future Industries Institute, University of South Australia, Mawson Lakes, South Australia 5095, Australia
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6
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Aliaga C, Rezende MC, Mena G. The effect of micellization on the EPR spectra and reactivity of 2,2,4,4-tetramethylpiperidinoxyl (TEMPO) radicals. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2016; 54:870-873. [PMID: 27412810 DOI: 10.1002/mrc.4485] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Revised: 06/22/2016] [Accepted: 07/08/2016] [Indexed: 06/06/2023]
Abstract
A series of 4-alkanoyloxy-2,2,6,6-tetramethylpiperidinoxyl radicals was prepared, and their reactivity in water vis-à-vis antioxidant Trolox was compared. Spectral (electron paramagnetic resonance) and dynamic-light-scattering measurements suggested the formation of micelles for the more hydrophobic members of the series. The observed increase in reactivity for the micelle-forming radicals reflected the increased local concentration of the radical fragment on the micellar interface. Copyright © 2016 John Wiley & Sons, Ltd.
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Affiliation(s)
- Carolina Aliaga
- Facultad de Química y Biología, Universidad de Santiago de Chile, Casilla 40 Correo 33, Santiago, Chile.
- Centro para el Desarrollo de la Nanociencia y la Nanotecnología (CEDENNA), Santiago, Chile.
| | - Marcos Caroli Rezende
- Facultad de Química y Biología, Universidad de Santiago de Chile, Casilla 40 Correo 33, Santiago, Chile
| | - Geraldine Mena
- Facultad de Química y Biología, Universidad de Santiago de Chile, Casilla 40 Correo 33, Santiago, Chile
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7
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Sisco E, Dake J. Detection of Low Molecular Weight Adulterants in Beverages by Direct Analysis in Real Time Mass Spectrometry. ANALYTICAL METHODS : ADVANCING METHODS AND APPLICATIONS 2016; 8:2971-2978. [PMID: 27335585 PMCID: PMC4911641 DOI: 10.1039/c6ay00292g] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Direct Analysis in Real Time Mass Spectrometry (DART-MS) has been used to detect the presence of non-narcotic adulterants in beverages. The non-narcotic adulterants that were examined in this work incorporated a number low molecular weight alcohols, acetone, ammonium hydroxide, and sodium hypochlorite. Analysis of the adulterants was completed by pipetting 1 µL deposits onto glass microcapillaries along with an appropriate dopant species followed by introduction into the DART gas stream. It was found that detection of these compounds in the complex matrices of common beverages (soda, energy drinks, etc.) was simplified through the use of a dopant species to allow for adduct formation with the desired compound(s) of interest. Other parameters that were investigated included DART gas stream temperature, in source collision induced dissociation, ion polarity, and DART needle voltage. Sensitivities of the technique were found to range from 0.001 % volume fraction to 0.1 % volume fraction, comparable to traditional analyses completed using headspace gas chromatography mass spectrometry (HS-GC/MS). Once a method was established using aqueous solutions, , fifteen beverages were spiked with each of the nine adulterants, to simulate real world detection, and in nearly all cases the adulterant could be detected either in pure form, or complexed with the added dopant species. This technique provides a rapid way to directly analyze beverages believed to be contaminated with non-narcotic adulterants at sensitivities similar to or exceeding those of traditional confirmatory analyses.
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Affiliation(s)
- Edward Sisco
- National Institute of Standards and Technology, Materials Measurement Science Division, Gaithersburg, MD, USA
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8
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Burgers PC, Holmes JL, Terlouwc JK. Metal ion hydrocarbon bidentate bonding in alkyl acetates, methyl alkanoates, alcohols and 1-alkenes: a comparative study. EUROPEAN JOURNAL OF MASS SPECTROMETRY (CHICHESTER, ENGLAND) 2016; 22:297-305. [PMID: 27900859 DOI: 10.1255/ejms.1440] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The relative affinity of the monovalent metal ions Li+, Na+, Cu+ and Ag+ towards a series of aliphatic alkyl acetates and some selected 1-alkenes (P) was examined using the kinetic method. A detailed analysis of the dissociation characteristics of a series of mixed metal-bound dimer ions of the type P1-M+-P2 and the evaluated proton affinities (PAs) of the monomers shows that the affinity of the cation towards long-chain alkyl acetates and alkenes (having a chain length ≤ C4) is markedly enhanced. In line with recent studies of nitriles, alcohols and methyl alkanoates, this is attributed to a bidentate interaction of the metal ion with the functional group or double bond and the aliphatic chain. In particular, the longer chain alkyl acetates, methyl alkanoates and alcohols show a remarkably similar behaviour with respect to silver ion hydrocarbon bonding. The Ag+ adducts of the alkyl acetates dissociate by loss of CH3COOH. This reaction becomes more pronounced at longer chain lengths, which points to metal ion bidentate formation in [Ag+···1-alkene] product ions having a long hydrocarbon chain. In the same vein, the heterodimers [1- hexene···Ag+···1-heptene] and [1- heptene···Ag+···1-octene] dissociate primarily into [Ag+···1-heptene] and [Ag+···1-octene] ions, respectively. Hydrocarbon bidentate formation in [Ag+···1-octene] also reveals itself by the reluctance of this ion to react with water in an ion trap, as opposed to [Ag+···1-hexene] which readily undergoes hydration.
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Affiliation(s)
- Peter C Burgers
- Department of Neurology, Laboratory of Neuro-Oncology, Erasmus Medical Center, Rotterdam, 3015 CN, The Netherlands.
| | - John L Holmes
- Department of Chemistry and Biological Sciences, University of Ottawa, 10 Marie Curie, Ottawa, Ontario K1N 6N5, Canada
| | - Johan K Terlouwc
- Department of Chemistry and Chemical Biology, McMaster University, Hamilton, ON, Canada L8S 4M1
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9
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Pasupuleti D, Pierce K, Eiceman G. Gas chromatography with tandem differential mobility spectrometry of fatty acid alkyl esters and the selective detection of methyl linolenate in biodiesels by dual-stage ion filtering. J Chromatogr A 2015; 1421:162-70. [DOI: 10.1016/j.chroma.2015.09.017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Revised: 09/04/2015] [Accepted: 09/04/2015] [Indexed: 10/23/2022]
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10
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Xiao C, Pérez LM, Russell DH. Effects of charge states, charge sites and side chain interactions on conformational preferences of a series of model peptide ions. Analyst 2015; 140:6933-44. [DOI: 10.1039/c5an00826c] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The factors affecting conformational preference of gas phase peptide ions are investigated by IM-MS and molecular dynamics simulation.
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Affiliation(s)
- Chunying Xiao
- Texas A&M University
- Department of Chemistry
- College Station
- USA
| | - Lisa M. Pérez
- Texas A&M University
- Department of Chemistry
- College Station
- USA
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11
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McAlpin CR, Voorhees KJ, Corpuz AR, Richards RM. Analysis of Lipids: Metal Oxide Laser Ionization Mass Spectrometry. Anal Chem 2012; 84:7677-83. [DOI: 10.1021/ac300688u] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Casey R. McAlpin
- Department of Chemistry
and Geochemistry, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Kent J. Voorhees
- Department of Chemistry
and Geochemistry, Colorado School of Mines, Golden, Colorado 80401, United States
| | - April R. Corpuz
- Department of Chemistry
and Geochemistry, Colorado School of Mines, Golden, Colorado 80401, United States
| | - Ryan M. Richards
- Department of Chemistry
and Geochemistry, Colorado School of Mines, Golden, Colorado 80401, United States
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12
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Pedersen CS, Lauritsen FR, Sysoev A, Viitanen AK, Mäkelä JM, Adamov A, Laakia J, Mauriala T, Kotiaho T. Characterization of proton-bound acetate dimers in ion mobility spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2008; 19:1361-1366. [PMID: 18635378 DOI: 10.1016/j.jasms.2008.05.024] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2008] [Revised: 05/26/2008] [Accepted: 05/26/2008] [Indexed: 05/26/2023]
Abstract
Ionized acetates were used as model compounds to describe gas-phase behavior of oxygen containing compounds with respect to their formation of dimers in ion mobility spectrometry (IMS). The ions were created using corona discharge at atmospheric pressure and separated in a drift tube before analysis of the ions by mass spectrometry. At the ambient operational temperature and pressure used in our instrument, all acetates studied formed dimers. Using a homolog series of n-alkyl-acetates, we found that the collision cross section of a dimer was smaller than that of a monomer with the same reduced mass. Our experiments also showed that the reduced mobility of acetate dimers with different functional groups increased in the order n-alkyl <or= branched chain alkyl <or= cyclo alkyl < aromat. For mixed n-alkyl dimers we found that the reduced mobility of acetate dimers having the same number of carbons, for example a dimer of acetyl acetate and hexyl acetate has the same reduced mobility as a dimer composed of two butyl acetates. The fundamental behavior of acetate monomers and dimers described in this paper will assist in a better understanding of the influence of dimer formation in ion mobility spectrometry.
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13
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Marotta E, Paradisi C. Positive ion chemistry of esters of carboxylic acids in air plasma at atmospheric pressure. JOURNAL OF MASS SPECTROMETRY : JMS 2005; 40:1583-9. [PMID: 16320290 DOI: 10.1002/jms.935] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Ionization of esters of carboxylic acids RCOOR' (R = H, alkyl; R' = alkyl) within the air plasma of the Atmospheric Pressure Chemical Ionization (APCI) source occurs largely via H(+)-transfer and, to a minor extent, via NO(+) association. The protonated ester MH(+) is normally observed as M(2)H(+) and as higher aggregates (M(3)H(+), M(3)H(+)(H(2)O)) also at high source temperature. The behavior of M(2)H(+) upon collisional activation is consistent with the reported dissociation of proton-bound dimers to MH(+) species that, in turn, fragment according to the known paths of lowest energy. In addition, other important product ions form within the plasma, some in very high relative abundance, which are attributed to ion-molecule condensation reactions between neutral M and either MH(+) or M(2)H(+) resulting in the elimination of CO, R'OH, alkene from the alkoxy moiety of the ester and HCOOH. A general scheme is proposed to account for the experimental observations, which suggest that the encounter complex formed between MH(+) and M or between M(2)H(+) and M may either collisionally relax to the protonated dimer or trimer, respectively, or react via covalent bond forming and cleaving steps to eliminate stable neutral molecules. The proposed scheme is supported by both the observed concentration dependence and the temperature dependence of the products relative abundances within the plasma. Such reactions can be the dominant process, as in the case of formate esters. A second significant ionization route involves addition of NO(+) to form M(n)NO(+) (n = 1, 2, 3). An additional product corresponding to [M(2)NO(+) - CO(2)] is also observed with iso- and n-butyl formate esters.
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Affiliation(s)
- Ester Marotta
- Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo 1, Italy
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14
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Malone M, Evans JJ. Determining the relative amounts of positional isomers in complex mixtures of triglycerides using reversed-phase high-performance liquid chromatography-tandem mass spectrometry. Lipids 2005; 39:273-84. [PMID: 15233407 DOI: 10.1007/s11745-004-1230-6] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A reversed-phase HPLC-tandem mass spectrometry (RP-HPLC-MS-MS) method was refined for the positional analysis of complex mixtures of TAG. This method has the advantages of speed, ease of automation, and specificity over traditional digestion-based methods for the positional analysis of TAG. Collision-induced dissociation (CID) of ammoniated TAG in an ion-trap mass spectrometer produced spectra that were dependent on the FA position. Dominant DAG fragments were formed from the loss of a FA moiety from the ammoniated TAG species. The loss of FA in the outer positions was favored over their loss in the central position. The combination of RP-HPLC and CID produced spectra that were free of the isotope effects that can complicate spectral interpretation in existing methods. The combination also provided selectivity based on the chromatographic fractionation of TAG, in addition to the selectivity inherent in the CID process. Proof-of-concept experiments were performed with binary mixtures of TAG from the SOS/SSO, OSO/OOS, and the PSO/POS/SPO positional isomer systems (where S is 18:0, stearic acid; O is 18:1 (cis-9), oleic acid; and P is 16:0, palmitic acid). Plots of fractional DAG fragment intensities vs. fractional composition of the binary mixtures were linear. These plots were used to determine the fractional composition of each of these isomeric systems in a variety of vegetable oils and animal fats. Current limitations, future developments, and applications of this method are discussed.
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Affiliation(s)
- Michael Malone
- Chemistry Department, University of Massachusetts Boston, Boston, Massachusetts 02125, USA
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15
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Physical Organic Chemistry of the Gas Phase. Reactivity Trends for Organic Cations. Top Curr Chem (Cham) 2003. [DOI: 10.1007/3-540-36113-8_1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/08/2023]
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16
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Guan Z. Identification and localization of the fatty acid modification in ghrelin by electron capture dissociation. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2002; 13:1443-1447. [PMID: 12484464 DOI: 10.1016/s1044-0305(02)00707-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Electron capture dissociation (ECD) has been demonstrated to be an effective fragmentation technique for characterizing the site and structure of the fatty acid modification in ghrelin, a 28-residue growth-hormone-releasing peptide that has an unusual ester-linked n-octanoyl (C8:0) modification at Ser-3. ECD cleaves 21 of 23 possible backbone amine bonds, with the product ions (c and z* ions) covering a greater amino acid sequence than those obtained by collisionally activated dissociation (CAD). Consistent with the ECD nonergodic mechanism, the ester-linked octanoyl group is retained on all backbone cleavage product ions, allowing for direct localization of this labile modification. In addition, ECD also induces the ester bond cleavage to cause the loss of octanoic acid from the ghrelin molecular ion; the elimination process is initiated by the capture of an electron at the protonated ester group, which is followed by the radical-site-initiated reaction known as alpha-cleavage. The chemical composition of the attached fatty acid can be directly obtained from the accurate Fourier transform ion cyclotron resonance (FTICR) mass measurement of the ester bond cleavage product ions.
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Affiliation(s)
- Ziqiang Guan
- Molecular Profiling Proteomics, Merck Research Laboratories, Rahway, New Jersey 07065, USA.
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17
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Fagerquist CK, Hellerstein MK, Faubert D, Bertrand MJ. Elimination of the concentration dependence in mass isotopomer abundance mass spectrometry of methyl palmitate using metastable atom bombardment. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2001; 12:754-761. [PMID: 11401166 DOI: 10.1016/s1044-0305(01)00227-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
An important problem in mass isotopomer abundance mass spectrometry (MIAMS) is the dependence of measured mass isotopomer abundances on sample concentration. We have evaluated the role of ionization energy on mass isotopomer abundance ratios of methyl palmitate as a function of sample concentration. Ionization energy was varied using electron impact ionization (EI) and metastable atom bombardment (MAB). The latter generates a beam of metastable species capable of ionizing analyte molecules by Penning ionization. We observed that ionization of methyl palmitate by EI (70 eV) showed the greatest molecular ion fragmentation and also showed the greatest dependence of relative isotopomer abundance ratios on sample concentration. Ionization using the 3P2 and 3P0 states of metastable krypton (9.92 and 10.56 eV, respectively) resulted in almost no molecular ion fragmentation, and the isotopomer abundances quantified were essentially independent of sample concentration. Ionization using the 3P2 and 3P0 states of metastable argon (11.55 and 11.72 eV, respectively) showed molecular ion fragmentation intermediate between that of EI and MAB(Kr) and showed an isotopomer concentration dependence which was less severe than that observed with EI but more severe than that observed with MAB(Kr). The observed decrease in the dependence of isotopomer abundance on sample concentration with a decrease in molecular ion fragmentation is consistent with the hypothesis that proton transfer from a fragment cation to a neutral molecule is the gas phase reaction mechanism responsible for the concentration dependence. Alternative explanations, e.g., hydrogen abstraction from a neutral molecule to a molecular cation, is not supported by these results. Moreover, the MAB ionization technique shows potential for eliminating one source of error in MIAMS measurements of methyl palmitate, in particular, and of fatty acids methyl esters, in general.
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Affiliation(s)
- C K Fagerquist
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, USA.
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18
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Current literature in mass spectrometry. JOURNAL OF MASS SPECTROMETRY : JMS 2001; 36:225-235. [PMID: 11345053 DOI: 10.1002/jms.89] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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