Compositional heterogeneity amongst salt-rich grains emitted from Enceladus’ subsurface ocean

2020 ◽  
Author(s):  
Zenghui Zou ◽  
Frank Postberg ◽  
Jon Hillier ◽  
Nozair Khawaja ◽  
Fabian Klenner ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Impact Ionization ◽  
Ionization Mass ◽  
Compositional Heterogeneity ◽  
Subsurface Ocean ◽  
Wide Range ◽  
Geochemical Models ◽  
Laboratory Analogue ◽  
Compositional Diversity ◽  
Dissolved Salts

<p>Salt-rich icy particles within Saturn’s E-Ring are relatively young (<~200 years), and originate from frozen aerosolized droplets of the salty seawater of Enceladus’ subsurface ocean, ejected into space, through fractures in the moon’s south polar region, within a plume of gas and ice particles. The salt-rich grains are therefore believed to reflect the composition of the ocean water. In situ mass spectra of the plume and E-ring icy particles, obtained by the Cosmic Dust Analyzer (CDA) impact ionization mass spectrometer onboard the Cassini spacecraft, indicate significant compositional diversity within the salt-rich population. Understanding the compositions of dissolved salts within the grains, and thus the ocean, can provide important constraints for geochemical models of Enceladus’ core/ocean environment.</p><p>To investigate and quantify variations in grain composition, a Laser Induced Liquid Beam Ion Desorption (LILBID) technique has been used to desorb and ionize a wide range of Enceladean ocean-like solutions containing dissolved salts. The resulting ions were then measured by a reflectron-type time of flight mass spectrometer. As the laser desorption mechanism simulates the ice grain impact process occurring on the CDA target, spectra produced in the laboratory from a large range of well-characterized salt solutions can be used to determine the CDA-applicable spectral appearances of substances within the ice grains emitted from Enceladus’ ocean.</p><p>Here we present the results of an investigation of CDA E-ring spectra, supported by laboratory analogue experiments, which show significant compositional heterogeneity within the salt-rich grains originating from Enceladus’ subsurface ocean. Two main spectral subtypes, representing endmember compositions within the salt-rich grains, are identified. These mass spectra are dominated by features from chloride-rich or carbonate-rich compounds and the laboratory detectability of other, additional, compounds within these brines is discussed.</p>

Composition of ultrafine particles in urban Beijing: Measurement using a thermal desorption chemical ionization mass spectrometer

2021 ◽  
Author(s):  
Xiaoxiao Li ◽  
Yuyang Li ◽  
Michael Lawler ◽  
Jiming Hao ◽  
James Smith ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Thermal Desorption ◽  
Ultrafine Particles ◽  
Chemical Ionization ◽  
Urban Atmosphere ◽  
Ionization Mass ◽  
Radioactive Materials ◽  
Desorption Chemical Ionization ◽  
Wide Range ◽  
Primary Emissions

<p>Ultrafine particles (UFPs) dominate the particle number population in the urban atmosphere and revealing their chemical composition is important. The thermal desorption chemical ionization mass spectrometer (TDCIMS) can semi-continuously measure UFP composition at the molecular level. We modified a TDCIMS and deployed it in urban Beijing. Radioactive materials in the TDCIMS for aerosol charging and chemical ionization were replaced by soft X-ray ionizers so that it can be operated in countries with tight regulations on radioactive materials. Protonated N-methyl-2-pyrrolidone ions were used as the positive reagent ion, which selectively detects ammonia and low-molecular weight-aliphatic amines and amides vaporized from the particle phase. With superoxide as the negative reagent ion, a wide range of inorganic and organic compounds were observed, including nitrate, sulfate, aliphatic acids with carbon numbers up to 18, and highly oxygenated CHO, CHON, and CHOS compounds. The latter two can be attributed to parent ions or the decomposition products of organonitrates and organosulfates/organosulfonates, respectively. Components from both primary emissions and secondary formation of UFPs were identified. Compared to the UFPs measured at forest and marine sites, those in urban Beijing contain more nitrogen-containing and sulfur-containing compounds. These observations illustrate unique features of the UFPs in this polluted urban environment and provide insights into their origins.</p>

scholarly journals Revisiting benzene cluster cations for the chemical ionization of dimethyl sulfide and select volatile organic compounds

2015 ◽  
Vol 8 (10) ◽  
pp. 10121-10157 ◽  
Author(s):  
M. J. Kim ◽  
M. C. Zoerb ◽  
N. R. Campbell ◽  
K. J. Zimmermann ◽  
B. W. Blomquist ◽  
...  
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Dimethyl Sulfide ◽  
Marine Boundary Layer ◽  
Ionization Mass ◽  
Select Group ◽  
Wide Range ◽  
Volatile Organic

Abstract. Benzene cluster cations were revisited as a sensitive and selective reagent ion for the chemical ionization of dimethyl sulfide (DMS) and a select group of volatile organic compounds (VOCs). Laboratory characterization was performed using both a new set of compounds (i.e. DMS, β-caryophyllene) as well as previously studied VOCs (i.e., isoprene, α-pinene). Using a field deployable chemical ionization time-of-flight mass spectrometer (CI-ToFMS), benzene cluster cations demonstrated high sensitivity (> 1 ncps ppt−1) to DMS, isoprene, and α-pinene standards. Parallel measurements conducted using a chemical-ionization quadrupole mass spectrometer, with a weaker electric field, demonstrated that ion-molecule reactions likely proceed through a combination of ligand-switching and direct charge transfer mechanisms. Laboratory tests suggest that benzene cluster cations may be suitable for the selective ionization of sesquiterpenes, where minimal fragmentation (< 25 %) was observed for the detection of β-caryophyllene, a bicyclic sesquiterpene. The field stability of benzene cluster cations using CI-ToFMS was examined in the marine boundary layer during the High Wind Gas Exchange Study (HiWinGS). The use of benzene cluster cation chemistry for the selective detection of DMS was validated against an atmospheric pressure ionization mass spectrometer. Measurements from the two instruments were highly correlated (R2=0.80) over a wide range of sampling conditions.

scholarly journals Constraining the response factors of an extractive electrospray ionization mass spectrometer for near-molecular aerosol speciation

2021 ◽  
Vol 14 (11) ◽  
pp. 6955-6972
Author(s):  
Dongyu S. Wang ◽  
Chuan Ping Lee ◽  
Jordan E. Krechmer ◽  
Francesca Majluf ◽  
Yandong Tong ◽  
...  
Keyword(s):  
Electrospray Ionization ◽  
Mass Spectrometer ◽  
Molecular Level ◽  
Ionization Mass ◽  
Molecular Response ◽  
Response Factor ◽  
Particle Phase ◽  
Aerosol Composition ◽  
Response Factors ◽  
Wide Range

Abstract. Online characterization of aerosol composition at the near-molecular level is key to understanding chemical reaction mechanisms, kinetics, and sources under various atmospheric conditions. The recently developed extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) is capable of detecting a wide range of organic oxidation products in the particle phase in real time with minimal fragmentation. Quantification can sometimes be hindered by a lack of available commercial standards for aerosol constituents, however. Good correlations between the EESI-TOF and other aerosol speciation techniques have been reported, though no attempts have yet been made to parameterize the EESI-TOF response factor for different chemical species. Here, we report the first parameterization of the EESI-TOF response factor for secondary organic aerosol (SOA) at the near-molecular level based on its elemental composition. SOA was formed by ozonolysis of monoterpene or OH oxidation of aromatics inside an oxidation flow reactor (OFR) using ammonium nitrate as seed particles. A Vocus proton-transfer reaction mass spectrometer (Vocus-PTR) and a high-resolution aerosol mass spectrometer (AMS) were used to determine the gas-phase molecular composition and the particle-phase bulk chemical composition, respectively. The EESI response factors towards bulk SOA coating and the inorganic seed particle core were constrained by intercomparison with the AMS. The highest bulk EESI response factor was observed for SOA produced from 1,3,5-trimethylbenzene, followed by those produced from d-limonene and o-cresol, consistent with previous findings. The near-molecular EESI response factors were derived from intercomparisons with Vocus-PTR measurements and were found to vary from 103 to 106 ion counts s−1 ppb−1, mostly within ±1 order of magnitude of their geometric mean of 104.6 ion counts s−1 ppb−1. For aromatic SOA components, the EESI response factors correlated with molecular weight and oxygen content and inversely correlated with volatility. The near-molecular response factors mostly agreed within a factor of 20 for isomers observed across the aromatics and biogenic systems. Parameterization of the near-molecular response factors based on the measured elemental formulae could reproduce the empirically determined response factor for a single volatile organic compound (VOC) system to within a factor of 5 for the configuration of our mass spectrometers. The results demonstrate that standard-free quantification using the EESI-TOF is possible.

scholarly journals Using collision-induced dissociation to constrain sensitivity of ammonia chemical ionization mass spectrometry (NH<sub>4</sub><sup>+</sup>-CIMS) to oxygenated volatile organic compounds

2018 ◽  
Author(s):  
Alexander Zaytsev ◽  
Martin Breitenlechner ◽  
Abigail R. Koss ◽  
Christopher Y. Lim ◽  
James C. Rowe ◽  
...  
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Ammonium Ion ◽  
Collision Induced Dissociation ◽  
Ionization Mass ◽  
Wide Range ◽  
Oxygenated Volatile Organic Compounds ◽  
Volatile Organic

Abstract. Chemical ionization mass spectrometers (CIMS) routinely detect hundreds of oxidized organic compounds in the atmosphere. A major limitation of these instruments is the uncertainty in their sensitivity to many of the detected ions. We describe the development of a new high-resolution time-of-flight chemical ionization mass spectrometer that operates in one of two ionization modes: using either ammonium ion ligand switching reactions as NH4+-CIMS or proton transfer reactions as PTR-MS. Switching between the modes can be done within two minutes. The NH4+-CIMS mode of the new instrument has sensitivities of up to 67 000 dcps ppbv−1 (duty cycle corrected ion counts per second/parts per billion by volume) and detection limits between 1 and 60 pptv at 2σ for a 1s integration time for numerous oxygenated volatile organic compounds. We present a mass spectrometric voltage scanning procedure based on collision-induced dissociation that allows us to determine the stability of ammonium-organic ions detected by the NH4+-CIMS. Using this procedure, we can effectively constrain the sensitivity of the ammonia chemical ionization mass-spectrometer to a wide range of detected oxidized volatile organic compounds for which no calibration standards exist. We demonstrate the application of this procedure by quantifying the composition of secondary organic aerosols in a series of laboratory experiments.

scholarly journals Revisiting benzene cluster cations for the chemical ionization of dimethyl sulfide and select volatile organic compounds

2016 ◽  
Vol 9 (4) ◽  
pp. 1473-1484 ◽  
Author(s):  
Michelle J. Kim ◽  
Matthew C. Zoerb ◽  
Nicole R. Campbell ◽  
Kathryn J. Zimmermann ◽  
Byron W. Blomquist ◽  
...  
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Dimethyl Sulfide ◽  
Marine Boundary Layer ◽  
Ionization Mass ◽  
Select Group ◽  
Wide Range ◽  
Volatile Organic

Abstract. Benzene cluster cations were revisited as a sensitive and selective reagent ion for the chemical ionization of dimethyl sulfide (DMS) and a select group of volatile organic compounds (VOCs). Laboratory characterization was performed using both a new set of compounds (i.e., DMS, β-caryophyllene) as well as previously studied VOCs (i.e., isoprene, α-pinene). Using a field deployable chemical-ionization time-of-flight mass spectrometer (CI-ToFMS), benzene cluster cations demonstrated high sensitivity (> 1 ncps ppt−1) to DMS, isoprene, and α-pinene standards. Parallel measurements conducted using a chemical-ionization quadrupole mass spectrometer, with a much weaker electric field, demonstrated that ion–molecule reactions likely proceed through a combination of ligand-switching and direct charge transfer mechanisms. Laboratory tests suggest that benzene cluster cations may be suitable for the selective ionization of sesquiterpenes, where minimal fragmentation (< 25 %) was observed for the detection of β-caryophyllene, a bicyclic sesquiterpene. The in-field stability of benzene cluster cations using CI-ToFMS was examined in the marine boundary layer during the High Wind Gas Exchange Study (HiWinGS). The use of benzene cluster cation chemistry for the selective detection of DMS was validated against an atmospheric pressure ionization mass spectrometer, where measurements from the two instruments were highly correlated (R2 > 0.95, 10 s averages) over a wide range of sampling conditions.

scholarly journals Molecular transformations of phenolic SOA during photochemical aging in the aqueous phase: competition among oligomerization, functionalization, and fragmentation

2015 ◽  
Vol 15 (20) ◽  
pp. 29673-29704
Author(s):  
L. Yu ◽  
J. Smith ◽  
A. Laskin ◽  
K. M. George ◽  
C. Anastasio ◽  
...  
Keyword(s):  
Phenolic Compounds ◽  
Mass Spectrometer ◽  
Reaction Pathway ◽  
Organic Aerosol ◽  
Ionization Mass ◽  
Vapor Pressures ◽  
Covalent Bonds ◽  
Wide Range ◽  
Open Ring ◽  
Photochemical Aging

Abstract. Organic aerosol is formed and transformed in atmospheric aqueous phases (e.g., cloud and fog droplets and deliquesced airborne particles containing small amounts of water) through a multitude of chemical reactions. Understanding these reactions is important for a predictive understanding of atmospheric aging of aerosols and their impacts on climate, air quality, and human health. In this study, we investigate the chemical evolution of aqueous secondary organic aerosol (aqSOA) formed during reactions of phenolic compounds with two oxidants – the triplet excited state of an aromatic carbonyl (3C&amp;ast;) and hydroxyl radical (•OH). Changes in the molecular composition of aqSOA as a function of aging time are characterized using an offline nanospray desorption electrospray ionization mass spectrometer (nano-DESI MS) whereas the real-time evolution of SOA mass, elemental ratios, and average carbon oxidation state (OSC) are monitored using an online aerosol mass spectrometer (AMS). Our results indicate that oligomerization is an important aqueous reaction pathway for phenols, especially during the initial stage of photooxidation equivalent to ∼ 2 h irradiation under midday, winter solstice sunlight in northern California. At later reaction times functionalization (i.e., adding polar oxygenated functional groups to the molecule) and fragmentation (i.e., breaking of covalent bonds) become more important processes, forming a large variety of functionalized aromatic and open-ring products with higher OSC values. Fragmentation reactions eventually dominate the photochemical evolution of phenolic aqSOA, forming a large number of highly oxygenated open-ring molecules with carbon numbers (nC) below 6. The average nC of phenolic aqSOA decreases while average OSC increases over the course of photochemical aging. In addition, the saturation vapor pressures C&amp;ast;) of dozens of the most abundant phenolic aqSOA molecules are estimated. A wide range of C&amp;ast; values is observed, varying from < 10-20 μg m-3 for functionalized phenolic oligomers to > 10 μg m-3 for small open-ring species. The detection of abundant extremely low volatile organic compounds (ELVOC) indicates that aqueous reactions of phenolic compounds are likely an important source of ELVOC in the atmosphere.

scholarly journals Molecular transformations of phenolic SOA during photochemical aging in the aqueous phase: competition among oligomerization, functionalization, and fragmentation

2016 ◽  
Vol 16 (7) ◽  
pp. 4511-4527 ◽  
Author(s):  
Lu Yu ◽  
Jeremy Smith ◽  
Alexander Laskin ◽  
Katheryn M. George ◽  
Cort Anastasio ◽  
...  
Keyword(s):  
Phenolic Compounds ◽  
Mass Spectrometer ◽  
Reaction Pathway ◽  
Organic Aerosol ◽  
Ionization Mass ◽  
Vapor Pressures ◽  
Covalent Bonds ◽  
Wide Range ◽  
Open Ring ◽  
Photochemical Aging

Abstract. Organic aerosol is formed and transformed in atmospheric aqueous phases (e.g., cloud and fog droplets and deliquesced airborne particles containing small amounts of water) through a multitude of chemical reactions. Understanding these reactions is important for a predictive understanding of atmospheric aging of aerosols and their impacts on climate, air quality, and human health. In this study, we investigate the chemical evolution of aqueous secondary organic aerosol (aqSOA) formed during reactions of phenolic compounds with two oxidants – the triplet excited state of an aromatic carbonyl (3C∗) and hydroxyl radical (•OH). Changes in the molecular composition of aqSOA as a function of aging time are characterized using an offline nanospray desorption electrospray ionization mass spectrometer (nano-DESI MS) whereas the real-time evolution of SOA mass, elemental ratios, and average carbon oxidation state (OSC) are monitored using an online aerosol mass spectrometer (AMS). Our results indicate that oligomerization is an important aqueous reaction pathway for phenols, especially during the initial stage of photooxidation equivalent to  ∼  2 h irradiation under midday winter solstice sunlight in Northern California. At later reaction times functionalization (i.e., adding polar oxygenated functional groups to the molecule) and fragmentation (i.e., breaking of covalent bonds) become more important processes, forming a large variety of functionalized aromatic and open-ring products with higher OSC values. Fragmentation reactions eventually dominate the photochemical evolution of phenolic aqSOA, forming a large number of highly oxygenated ring-opening molecules with carbon numbers (nC) below 6. The average nC of phenolic aqSOA decreases while average OSC increases over the course of photochemical aging. In addition, the saturation vapor pressures (C∗) of dozens of the most abundant phenolic aqSOA molecules are estimated. A wide range of C∗ values is observed, varying from < 10−20 µg m−3 for functionalized phenolic oligomers to > 10 µg m−3 for small open-ring species. The detection of abundant extremely low-volatile organic compounds (ELVOC) indicates that aqueous reactions of phenolic compounds are likely an important source of ELVOC in the atmosphere.

Experiments for the detection of microbial biosignatures in ice grains from Europa and Enceladus

2021 ◽  
Author(s):  
Miriam Pavlista ◽  
Janine Bönigk ◽  
Fabian Klenner ◽  
Maryse Napoleoni ◽  
Jonathan Hillier ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Mass Spectra ◽  
Impact Ionization ◽  
Membrane Lipids ◽  
High Sensitivity ◽  
Building Blocks ◽  
Polar Molecules ◽  
Ionization Mass ◽  
Mass Spectrometers ◽  
Wide Range

&lt;div&gt; &lt;p&gt;Detecting and identifying biosignatures is key to the search for life on extraterrestrial ocean worlds. Saturn&amp;#8217;s moon Enceladus emits a plume of gas and water ice grains, formed from its subsurface ocean, into space. A similar phenomenon is suspected to occur on Jupiter&amp;#8217;s moon Europa. Impact Ionization mass spectrometers, such as the Cosmic Dust Analyzer (CDA) onboard the past Cassini mission or the Surface Dust Analyzer (SUDA) on board the upcoming Europa Clipper mission, can sample the emitted ice grains, rendering the ocean accessible for compositional analysis by spacecraft flybys. The CDA data collected in the Saturnian system showed that Enceladus&amp;#8217; ocean is salty [1] and contains a variety of organic material, such as complex macromolecules [2] and low mass volatile compounds, the latter of which potentially act as amino acid precursors and are capable of interacting within or near Enceladus&amp;#8217; hydrothermal vent system [4], or Enceladus&amp;#8217; porous rocky core [5]. Although these findings enhance Enceladus&amp;#8217; relevance as a potential habitable environment, biosignatures have so far not been identified.&lt;/p&gt; &lt;p&gt;Interpreting the space-based icy grain data requires on-ground calibration via analogue experiments. The Laser Induced Liquid Beam Ion Desorption (LILBID) technique is capable of accurately reproducing the mass spectra of ice grains recorded in space [6]. Previous LILBID experiments have shown that bioessential molecules, namely amino acids, fatty acids, and peptides can be detected in the ice grains [7], and that abiotic and biotic formation processes of these molecules can be distinguished from each other [8]. The next steps are to investigate whether building blocks of bacteria, such as membrane lipids &amp;#8211; indicators for earthlike microbial life - can also be detected in ice grains and characterized using future impact ionization mass spectrometers. To predict their spectral appearance in impact ionization mass spectra, high sensitivity LILBID experiments on extracts from Escherichia Coli and Sphingopyxis alaskensis were performed. Spectra of lipids, and the corresponding aqueous phases produced during their extraction, potentially containing polar molecules, were produced using increasingly NaCl-rich matrices, designed to mimic the salty ocean of Enceladus or Europa.&lt;/p&gt; &lt;p&gt;In the mass spectra, we identify fragments characteristic for the building blocks of bacteria, such as fatty acids deriving from the bacteria&amp;#8217;s membrane lipids. Sensitivity to lipid fragments and polar molecules decreases with rising salt concentration. These spectra, as well as those of other biosignatures,&amp;#160; have been incorporated into a comprehensive database, to provide comparable analogue data of a wide range of compounds applicable to future impact ionization mass spectrometers.&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; References&lt;/div&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;[1] Postberg et al. (2009) Nature 459:1098&amp;#8211;1101, [2] Postberg et al. (2018) Nature 558:564&amp;#8211;568, [3] Khawaja et al. (2019) Mon Not R Astron Soc 489:5231&amp;#8211;5243, [4] Hsu et al. (2015) Nature 519:207&amp;#8211; 210, [5] Choblet at al. (2017) Nat Astron 1:841-847, [6] Klenner et al. (2019) Rapid Commun Mass Spectrom 33:1751&amp;#8211;1760, [7] Klenner et al. (2020) Astrobiology 20:179&amp;#8211;189, [8] Klenner et al. (2020) Astrobiology 20: 1168&amp;#8211;1184.&lt;/p&gt;

scholarly journals Constraining the response factors of an extractive electrospray ionization mass spectrometer for near-molecular aerosol speciation

2021 ◽  
Author(s):  
Dongyu S. Wang ◽  
Chuan Ping Lee ◽  
Jordan E. Krechmer ◽  
Francesca Majluf ◽  
Yandong Tong ◽  
...  
Keyword(s):  
Electrospray Ionization ◽  
Mass Spectrometer ◽  
Molecular Level ◽  
Ionization Mass ◽  
Molecular Response ◽  
Response Factor ◽  
Particle Phase ◽  
Aerosol Composition ◽  
Response Factors ◽  
Wide Range

Abstract. Online characterization of aerosol composition at the near-molecular level is key to understanding chemical reaction mechanisms, kinetics, and sources under various atmospheric conditions. The recently developed extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) is capable of detecting a wide range of organic oxidation products in the particle phase in real time with minimal fragmentation. Quantification can sometimes be hindered by a lack of available commercial standards for aerosol constituents, however. Good correlations between the EESI-TOF and other aerosol speciation techniques have been reported, though no attempts have yet been made to parameterize the EESI-TOF response factor for different chemical species. Here, we report the first parameterization of the response factors of the EESI-TOF for secondary organic aerosol (SOA) at the near-molecular level based on their elemental composition. SOA was formed by ozonolysis of monoterpenes or OH-oxidation of aromatics inside an oxidation flow reactor (OFR) using ammonium nitrate as seed particles. A Vocus proton-transfer reaction mass spectrometer (Vocus-PTR) and a high-resolution aerosol mass spectrometer (AMS) were used to determine the gas phase molecular composition and the particle phase bulk chemical composition, respectively. The EESI response factors towards bulk SOA and the inorganic coating were constrained by intercomparison with the AMS. The highest bulk EESI response factor was observed for SOA produced from 1,3,5-trimethylbenzene, followed by those produced from d-limonene and o-cresol, consistent with previous findings. The near-molecular EESI response factors were derived from intercomparisons with Vocus-PTR measurements, and were found to vary from 103 to 106 ions s−1 ppb−1, mostly within ±1 order of magnitude of their geometric mean of 104.5 ions s−1 ppb−1. For aromatic SOA components, the EESI response factors correlated with molecular weight and oxygen content, and inversely correlated with volatility. The near-molecular response factors agreed within a factor of 20 for isomers observed across the aromatics and biogenic systems. Parameterization of the near-molecular response factors based on the measured elemental formulae could reproduce the empirically determined response factor for a single VOC system to within a factor of 5 for the configuration of our mass spectrometers. Results demonstrate that standard-free quantification using EESI-TOF is possible.

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