Methods to extract molecular and bulk chemical information from series of complex mass spectra with limited mass resolution

Stark, Harald; Yatavelli, R. L. N.; Thompson, Samantha L.; Kimmel, Joel R.; Cubison, M. J.; Chhabra, P. S.; Canagaratna, Manjula R.; Jayne, John T.; Worsnop, Douglas R.; Jimenez, José L.

doi:10.1016/j.ijms.2015.08.011

Cited by 105 publications

(162 citation statements)

References 33 publications

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“…During measurements the mass spectrometer was operated at a maximum mass resolution of 4000 and was tuned in "declustering mode", such that the acetate reagent ions are primarily in the form of bare ions. 21,24 The indoor and outdoor CIMS measurements were conducted from 1-6 and 8-10 May 2014, respectively. Indoor and outdoor measurements could not be made on the same day because the 6 CIMS is too large and the set-up time too long to be able to sample from different locations in short time intervals.…”

Section: Methodsmentioning

confidence: 99%

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Gas-Phase Carboxylic Acids in a University Classroom: Abundance, Variability, and Sources

Liu

Thompson

Stark

et al. 2017

Environ. Sci. Technol.

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100

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Gas-phase carboxylic acids are ubiquitous in ambient air, yet their indoor occurrence and abundance are poorly characterized. To fill this gap, we measured gas-phase carboxylic acids in real-time inside and outside of a university classroom using a high-resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS) equipped with an acetate ion source. A wide variety of carboxylic acids were identified indoors and outdoors, including monoacids, diacids, hydroxy acids, carbonyl acids, and aromatic acids. An empirical parametrization was derived to estimate the sensitivity (ion counts per ppt of the analytes) of the HRToF-CIMS to the acids. The campaign-average concentration of carboxylic acids measured outdoors was 1.0 ppb, with the peak concentration occurring in daytime. The average indoor concentration of carboxylic acids was 6.8 ppb, of which 87% was contributed by formic and lactic acid. While carboxylic acids measured outdoors displayed a single daytime peak, those measured indoors displayed a daytime and a nighttime peak. Besides indoor sources such as off-gassing of building materials, evidence for acid production from indoor chemical reactions with ozone was found. In addition, some carboxylic acids measured indoors correlated to CO in daytime, suggesting that human occupants may contribute to their abundance either through direct emissions or surface reactions.

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Section: Methodsmentioning

confidence: 99%

“…The analysis algorithm is described by Stark et al. 24 The peaks in the indoor CIMS spectra were fitted using the Tofware multi-peak fitting algorithm. An ion list for the fitted peaks was generated by assigning the peaks to possible ion elemental compositions.…”

Section: Methodsmentioning

confidence: 99%

Gas-Phase Carboxylic Acids in a University Classroom: Abundance, Variability, and Sources

Liu

Thompson

Stark

et al. 2017

Environ. Sci. Technol.

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100

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“…The post-processing software "Tofware" utilised for ToF-ACSM analysis uses a peak deconvolution routine where the peak positions are defined a priori and held fixed in the fitting procedure, based on the methodology utilised by the PIKA software of the ToF-AMS community (DeCarlo et al, 2006;Sueper, 2008). EI ionisation, as is used in the ToF-ACSM, tends to ionise and fragment the molecules in a very consistent manner.…”

Section: Peak-fitting Methodologymentioning

confidence: 99%

Applications and limitations of constrained high-resolution peak fitting on low resolving power mass spectra from the ToF-ACSM

et al. 2016

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Abstract. The applicability, methods and limitations of constrained peak fitting on mass spectra of low mass resolving power (m∕Δm50 ∼ 500) recorded with a time-of-flight aerosol chemical speciation monitor (ToF-ACSM) are explored. Calibration measurements as well as ambient data are used to exemplify the methods that should be applied to maximise data quality and assess confidence in peak-fitting results. Sensitivity analyses and basic peak fit metrics such as normalised ion separation are employed to demonstrate which peak-fitting analyses commonly performed in high-resolution aerosol mass spectrometry are appropriate to perform on spectra of this resolving power. Information on aerosol sulfate, nitrate, sodium chloride, methanesulfonic acid as well as semi-volatile metal species retrieved from these methods is evaluated. The constants in a commonly used formula for the estimation of the mass concentration of hydrocarbon-like organic aerosol may be refined based on peak-fitting results. Finally, application of a recently published parameterisation for the estimation of carbon oxidation state to ToF-ACSM spectra is validated for a range of organic standards and its use demonstrated for ambient urban data.

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“…Past work has proposed using desorption kinetics inside an inlet as a technique for identifying compounds (Schuhfried et al, 2012), and the model presented here can be used in a similar way. Another possible application is to induce time separation among different compounds that are otherwise indistinguishable to the analytical instrumentation (e.g., compounds with the same accurate mass in chemical ionization mass spectrometry (CIMS); Stark et al, 2015), since the c * of multifunctional compounds with the same molecular formula can often differ by 5 orders of magnitude (Krechmer et al, 2015). The separation in time can then be exploited via manual analyses or factor analysis techniques (e.g., Ulbrich et al, 2009).…”

Section: Effect Of Instrumentation On Delaysmentioning

confidence: 99%

Effects of gas–wall partitioning in Teflon tubing and instrumentation on time-resolved measurements of gas-phase organic compounds

et al. 2017

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Abstract. Recent studies have demonstrated that organic compounds can partition from the gas phase to the walls in Teflon environmental chambers and that the process can be modeled as absorptive partitioning. Here these studies were extended to investigate gas-wall partitioning of organic compounds in Teflon tubing and inside a protontransfer-reaction mass spectrometer (PTR-MS) used to monitor compound concentrations. Rapid partitioning of C 8 -C 14 2-ketones and C 11 -C 16 1-alkenes was observed for compounds with saturation concentrations (c * ) in the range of 3 × 10 4 to 1 × 10 7 µg m −3 , causing delays in instrument response to step-function changes in the concentration of compounds being measured. These delays vary proportionally with tubing length and diameter and inversely with flow rate and c * . The gas-wall partitioning process that occurs in tubing is similar to what occurs in a gas chromatography column, and the measured delay times (analogous to retention times) were accurately described using a linear chromatography model where the walls were treated as an equivalent absorbing mass that is consistent with values determined for Teflon environmental chambers. The effect of PTR-MS surfaces on delay times was also quantified and incorporated into the model. The model predicts delays of an hour or more for semivolatile compounds measured under commonly employed conditions. These results and the model can enable better quantitative design of sampling systems, in particular when fast response is needed, such as for rapid transients, aircraft, or eddy covariance measurements. They may also allow estimation of c * values for unidentified organic compounds detected by mass spectrometry and could be employed to introduce differences in time series of compounds for use with factor analysis methods. Best practices are suggested for sampling organic compounds through Teflon tubing.

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Methods to extract molecular and bulk chemical information from series of complex mass spectra with limited mass resolution

Abstract: 15 16 17 18 19 20 21 Keywords 22 Chemical ionization; high-resolution time-of-flight mass spectrometry; atmospheric measurements; 23 analysis of mass spectra; 24 © 2015. This manuscript version is made available under the Elsevier user license

Cited by 105 publications

References 33 publications

Gas-Phase Carboxylic Acids in a University Classroom: Abundance, Variability, and Sources

Gas-Phase Carboxylic Acids in a University Classroom: Abundance, Variability, and Sources

Applications and limitations of constrained high-resolution peak fitting on low resolving power mass spectra from the ToF-ACSM

Effects of gas–wall partitioning in Teflon tubing and instrumentation on time-resolved measurements of gas-phase organic compounds

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