Ultrahigh-resolution Mass Spectrometer Research Articles

Extraction, purification, and clumped isotope analysis of methane (Δ13CDH3 and Δ12CD2H2) from sources and the atmosphere

Abstract. Measurements of the clumped isotope anomalies (Δ13CDH3 and Δ12CD2H2) of methane have shown potential for constraining methane sources and sinks. At Utrecht University, we use the Thermo Scientific Ultra high-resolution isotope-ratio mass spectrometer to measure the clumped isotopic composition of methane emitted from various sources and directly from the atmosphere. We have developed an extraction system with three sections for extracting and purifying methane from high (> 1 %), medium (0.1 % to 1 %), and low-concentration (< 0.1 %) samples, including atmospheric air (∼ 2 ppm = 0.0002 %). Depending on the methane concentration, a quantity of sample gas is processed that delivers 3 ± 1 mL of pure methane, which is the quantity typically needed for one clumped isotope measurement. For atmospheric air with a methane mole fraction of 2 ppm, we currently process up to 1100 L of air. The analysis is performed on pure methane, using a dual-inlet setup. The complete measurement time for all isotope signatures is about 20 h for one sample. The mean internal precision values of sample measurements are 0.3 ± 0.1 ‰ for Δ13CDH3 and 2.4 ± 0.8 ‰ for Δ12CD2H2. The long-term reproducibility, obtained from repeated measurements of a constant target gas, over almost 3 years, is around 0.15 ‰ for Δ13CDH3 and 1.2 ‰ for Δ12CD2H2. The measured clumping anomalies are calibrated via the Δ13CDH3 and Δ12CD2H2 values of the reference CH4 used for the dual-inlet measurements. These were determined through isotope equilibration experiments at temperatures between 50 and 450 °C. We describe in detail the optimized sampling, extraction, purification, and measurement technique followed in our laboratory to measure the clumping anomalies of methane precisely and accurately. This paper highlights the extraction and one of the first global measurements of the clumping anomalies of atmospheric methane.

Molecular-Level Insights into the Relationship between Volatility of Organic Aerosol Constituents and PM2.5 Air Pollution Levels: A Study with Ultrahigh-Resolution Mass Spectrometry.

Volatility of organic aerosols (OAs) significantly influences new particle formation and the occurrence of particulate air pollution. However, the relationship between the volatility of OA and the level of particulate air pollution (i.e., particulate matter concentration) is not well understood. In this study, we compared the chemical composition (identified by an ultrahigh-resolution Orbitrap mass spectrometer) and volatility (estimated based on a predeveloped parametrization method) of OAs in urban PM2.5 (particulate matter with aerodynamic diameter ≤ 2.5 μm) samples from seven German and Chinese cities, where the PM2.5 concentration ranged from a light (14 μg m-3) to heavy (319 μg m-3) pollution level. A large fraction (71-98%) of compounds in PM2.5 samples were attributable to intermediate-volatility organic compounds (IVOCs) and semivolatile organic compounds (SVOCs). The fraction of low-volatility organic compounds (LVOCs) and extremely low-volatility organic compounds (ELVOCs) decreased from clean (28%) to heavily polluted urban regions (2%), while that of IVOCs increased from 34 to 62%. We found that the average peak area-weighted volatility of organic compounds in different cities showed a logarithmic correlation with the average PM2.5 concentration, indicating that the volatility of urban OAs increases with the increase of air pollution level. Our results provide new insights into the relationship between OA volatility and PM pollution levels and deepen the understanding of urban air pollutant evolution.

6-Plex mdSUGAR Isobaric-Labeling Guide Fingerprint Embedding for Glycomics Analysis.

Glycans are vital biomolecules with diverse functions in biological processes. Mass spectrometry (MS) has become the most widely employed technology for glycomics studies. However, in the traditional data-dependent acquisition mode, only a subset of the abundant ions during MS1 scans are isolated and fragmented in subsequent MS2 events, which reduces reproducibility and prevents the measurement of low-abundance glycan species. Here, we reported a new method termed 6-plex mdSUGAR isobaric-labeling guide fingerprint embedding (MAGNI), to achieve multiplexed, quantitative, and targeted glycan analysis. The glycan peak signature was embedded by a triplicate-labeling strategy with a 6-plex mdSUGAR tag, and using ultrahigh-resolution mass spectrometers, the low-abundance glycans that carry the mass fingerprints can be recognized on the MS1 spectra through an in-house developed software tool, MAGNIFinder. These embedded unique fingerprints can guide the selection and fragmentation of targeted precursor ions and further provide rich information on glycan structures. Quantitative analysis of two standard glycoproteins demonstrated the accuracy and precision of MAGNI. Using this approach, we identified 304 N-glycans in two ovarian cancer cell lines. Among them, 65 unique N-glycans were found differentially expressed, which indicates a distinct glycosylation pattern for each cell line. Remarkably, 31 N-glycans can be quantified in only 1 × 103 cells, demonstrating the high sensitivity of our method. Taken together, our MAGNI method offers a useful tool for low-abundance N-glycan characterization and is capable of determining small quantitative differences in N-glycan profiling. Therefore, it will be beneficial to the field of glycobiology and will expand our understanding of glycosylation.

Chemical Characterization of Rural Organic Aerosol in the North China Plain Using Ultrahigh-Resolution Mass Spectrometry

Atmospheric organic aerosol (OA) affects air quality and human health. However, compared with urban areas, the chemical composition and temporal distribution of OA in rural regions are still not well understood. In this study, one-year atmospheric particles with an aerodynamic equivalent diameter of ≤2.5 μm (PM2.5) were collected at a rural site in Quzhou County, the North China Plain (NCP), from August 2020 to July 2021. OA in PM2.5 samples were analyzed with an ultrahigh-performance liquid chromatograph (UHPLC) coupled to an ultrahigh-resolution Orbitrap mass spectrometer in negative mode (ESI−). The results show that the chemical composition and properties of OA varied in different seasons. According to the hierarchical cluster analysis, the molecular formulas of winter OA were close to those in spring, whereas the chemical composition of OA in summer and autumn was similar. The O/C ratio of summer OA was the highest at 1.21, followed by that in autumn (0.92) and spring (0.87), while the winter OA had the lowest O/C ratio of 0.64. It indicates that, compared to the other three seasons, OA underwent more intense oxidation processes in the summer. Moreover, winter OA contained more aromatic compounds with a relative peak abundance fraction of 40%, which may be related to anthropogenic sources (e.g., coal burning) in the winter in the NCP. In addition, biomass burning is considered an important source of OA in the rural region of Quzhou County, the NCP, in all seasons.

Sample preparation for structural mass spectrometry via polyacrylamide gel electrophoresis.

Mass spectrometry is an analytical technique that can detect protein molecules with high sensitivity. Its use is not limited to the mere identification of protein components in biological samples, but is recently being utilized for large-scale analysis of protein structures in vivo as well. Top-down mass spectrometry with an ultra-high resolution mass spectrometer, for example, ionizes proteins in their intact state and allows rapid analysis of their chemical structure, which is used to determine proteoform profiles. Furthermore, cross-linking mass spectrometry, which analyzes enzyme-digested fragments of chemically cross-linked protein complexes, allows acquisition of conformational information on protein complexes in multimolecular crowding environments. In the analysis workflow of structural mass spectrometry, prior fractionation of crude biological samples is an effective way to obtain more detailed structural information. Polyacrylamide gel electrophoresis (PAGE), known as a simple and reproducible means of protein separation in biochemistry, is one example of an excellent high-resolution sample prefractionation tool for structural mass spectrometry. This chapter describes elemental technologies for PAGE-based sample prefractionation including Passively Eluting Proteins from Polyacrylamide gels as Intact species for Mass Spectrometry (PEPPI-MS), a highly efficient method for intact in-gel protein recovery, and Anion-Exchange disk-assisted Sequential sample Preparation (AnExSP), a rapid enzymatic digestion method using a solid-phase extraction microspin column for gel-recovered proteins, in addition to presenting detailed experimental protocols and examples of their use for structural mass spectrometry.

Molecular Characterization of Formulated Lubricants and Additive Packages Using Kendrick Mass Defect Determined by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry.

Formulated lubricants correspond to high value products used for several applications in automotive, industrial, medicinal, and agro-food sectors. They correspond to complex matrices composed of approximately 80% of base oils (mineral or synthetic) and of about 20% of additives. Additives are generally low molecular weight polymeric molecules with a great diversity of elements. To characterize such complex compositions at the molecular level, ultrahigh resolution mass spectrometers are required. Two formulated lubricants and two additive packages were analyzed by Fourier transform ion cyclotron resonance mass spectrometry in direct infusion. Atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) sources were used to have an exhaustive characterization of the samples. The Kendrick mass defects (KMD) plot is a widespread representation to characterize polymeric molecules. Here, the terms apparent mass defect and apparent Kendrick mass defects (aKMD) values were introduced to consider the uncertainty on nominal mass determination. Several additive families including alkyldiphenylamines, trisalkylphenylthiophosphoric acid, zinc dithiophosphates, bisuccinimide dispersants, and their derivatives were observed by APCI(+). ESI(-) also presented a use for the selective ionization of acidic compounds including sulfonates, phenates, and sulfur phenate molecules. The specific aKMD values and polydispersity of many additive families have been reported to create a database of additives. Overall, this study demonstrated the great utility of the aKMD approach and the use of the ESI/APCI combination for a simple and fast characterization of formulated lubricant and additive package samples.

LC-HRMS based method for suspect/non-targeted screening for biomarkers of chemical exposure in human urine

Every day we are exposed to a cocktail of anthropogenic compounds many of which are biologically active and capable of inducing negative effects. The simplest way to monitor contaminants in a population is via human biomonitoring (HBM), however conventional targeted approaches require foreknowledge of chemicals of concern, often have compound specific extractions and provide information only for those compounds. This study developed an extraction process for human biomarkers of interest (BoE) in urine that is less compound specific. Combining this with an ultra-high resolution mass spectrometer capable of operating in full scan, and a suspect and non-targeted analysis (SS/NTA) approach, this method provides a more holistic characterization of human exposure. Sample preparation development was based on enzymatically hydrolysed urine spiked with 34 native standards and extracted by solid-phase extraction (SPE). HRMS data was processed by MzMine2 and 80% of standards were identified in the final data matrix using typical NTA data processing procedures.

Vacuum Laser Photoionization inside the C-trap of an Orbitrap Mass Spectrometer: Resonance-Enhanced Multiphoton Ionization High-Resolution Mass Spectrometry.

State-of-the-art mass spectrometry with ultraviolet (UV) photoionization is mostly limited to time-of-flight (ToF) mass spectrometers with 1000-10 000 m/Δm mass resolution. However, higher resolution and higher spectral dynamic range mass spectrometry may be indispensable in complex mixture characterization. Here, we present the concept, implementation, and initial evaluation of a compact ultrahigh-resolution mass spectrometer with gas-phase laser ionization. The concept is based on direct laser photoionization in the ion accumulation and ejection trap (C-trap) of an Orbitrap mass spectrometer. Resonance-enhanced multiphoton ionization (REMPI) using 266 nm UV pulses from a frequency-quadrupled Nd:YAG laser was applied for selective and efficient ionization of monocyclic and polycyclic aromatic hydrocarbons. The system is equipped with a gas inlet for volatile compounds and a heated gas chromatography coupling. The former can be employed for rapid system m/z-calibration and performance evaluation, whereas the latter enables analysis of semivolatile and higher-molecular-weight compounds. The capability to evaluate complex mixtures is demonstrated for selected petrochemical materials. In these experiments, several hundred to over a thousand compounds could be attributed with a root-mean-square mass error generally below 1 ppm and a mass resolution of over 140 000 at 200 m/z. Isobaric interferences could be resolved, and narrow mass splits, such as 3.4 mDa (SH4/C3), are determined. Single laser shots provided limits of detection in the 20-ppb range for p-xylene and 1,2,4-trimethylbenzene, similar to compact vacuum REMPI-ToF systems.

An Automated Methodology for Non-targeted Compositional Analysis of Small Molecules in High Complexity Environmental Matrices Using Coupled Ultra Performance Liquid Chromatography Orbitrap Mass Spectrometry.

The life-critical matrices of air and water are among the most complex chemical mixtures that are ever encountered. Ultrahigh-resolution mass spectrometers, such as the Orbitrap, provide unprecedented analytical capabilities to probe the molecular composition of such matrices, but the extraction of non-targeted chemical information is impractical to perform via manual data processing. Automated non-targeted tools rapidly extract the chemical information of all detected compounds within a sample dataset. However, these methods have not been exploited in the environmental sciences. Here, we provide an automated and (for the first time) rigorously tested methodology for the non-targeted compositional analysis of environmental matrices using coupled liquid chromatography–mass spectrometric data. First, the robustness and reproducibility was tested using authentic standards, evaluating performance as a function of concentration, ionization potential, and sample complexity. The method was then used for the compositional analysis of particulate matter and surface waters collected from worldwide locations. The method detected >9600 compounds in the individual environmental samples, arising from critical pollutant sources, including carcinogenic industrial chemicals, pesticides, and pharmaceuticals among others. This methodology offers considerable advances in the environmental sciences, providing a more complete assessment of sample compositions while significantly increasing throughput.

Comparison of Heated Electrospray Ionization and Nanoelectrospray Ionization Sources Coupled to Ultra-High-Resolution Mass Spectrometry for Analysis of Highly Complex Atmospheric Aerosol Samples.

Direct infusion analysis using soft ionization techniques coupled to ultra-high-resolution mass spectrometers (UHRMS) allows screening of thousands of organic species in complex samples. Despite the high analytical throughput of direct infusion, this technique is known to be prone to matrix effects caused by changes in the ionization efficiency of an analyte, ion suppression, or enhancement due to the presence of certain compounds and inorganic salts in the sample. In this study we compared two soft ionization sources, that is, heated electrospray ionization (HESI) and nano-ESI for the analysis of atmospheric aerosol samples in the negative ionization mode. In-source fragmentation tests were conducted and experiments involving sample desalting through solid-phase extraction (SPE) with a reversed phase functionalized polymeric sorbent and spiking samples with inorganic salt were performed. Both ionization sources showed specific advantages and disadvantages for the direct infusion analysis of atmospheric aerosol extracts. The mass spectra of aerosol samples analyzed using HESI contained a large number of high molecular weight homologues containing sulfur and nitrogen, suggesting that this source is prone to formation of salt adducts and noncovalent compounds in samples enriched with inorganic salts. Data from the same aerosol sample extracts analyzed using nanoelectrospray ionization (nano-ESI) show less adduct formation; however, a decrease in the number of homologues was observed, as well as loss of molecules at higher mass range, indicating that the nano-ESI source is more prone to ion suppression. Irrespective of ionization source, SPE pretreatment significantly improved ion recoveries for organic species with nonpolar and moderately polar functional groups, but lower recoveries were obtained for highly oxygenated molecules. Therefore, while SPE reduced in-source adduct formation, it also limited the range of compounds identified through a single analysis.

Improved Mass Accuracy and Isotope Confirmation through Alignment of Ultrahigh-Resolution Mass Spectra of Complex Natural Mixtures

Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) is one of the state-of-the-art methods to analyze complex natural organic mixtures. The precision of detected masses is crucial for molecular formula attribution. Random errors can be reduced by averaging multiple measurements of the same mass, but because of limited availability of ultrahigh-resolution mass spectrometers, most studies cannot afford analyzing each sample multiple times. Here we show that random errors can be eliminated also by averaging mass spectral data from independent environmental samples. By averaging the spectra of 30 samples analyzed on our 15 T instrument we reach a mass precision comparable to a single spectrum of a 21 T instrument. We also show that it is possible to accurately and reproducibly determine isotope ratios with FT-ICR-MS. Intensity ratios of isotopologues were improved to a degree that measured deviations were within the range of natural isotope fractionation effects. In analogy to δ13C in environmental studies, we propose Δ13C as an analytical measure for isotope ratio deviances instead of widely employed C deviances. In conclusion, here we present a simple tool, extensible to Orbitrap-based mass spectrometers, for postdetection data processing that significantly improves mass accuracy and the precision of intensity ratios of isotopologues at no extra cost.

Formation of highly oxygenated multifunctional compounds from cross-reactions of carbonyl compounds in the atmospheric aqueous phase

There is increasing evidence that aqueous-phase atmospheric chemistry is an important source of secondary organic aerosols (SOA), but this chemistry is currently not adequately represented in atmospheric models due to the missing information on most products. The main focus of this study is to provide molecular-level insight into the photosensitized reaction mechanism of pyruvic acid (PA) alone in the atmospheric aqueous phase, and of mixtures of PA with glyoxal (GL), a typical and widely occurring carbonyl compound. With two ultrahigh resolution mass spectrometers, ORBITRAP and FT-ICR-MS, a broad and complex spectrum of organic products were unambiguously identified. The detected formation of organic compounds illustrates the progression from C3 to C20 molecules through direct PA photolysis and irradiation of PA + GL. The performed ab-initio calculations indicate that cross-reactions (i.e., PA + GL) are more likely than self-reactions (i.e., PA alone) in clouds and aerosol deliquescent particles. Hence, this result implies that photosensitizers like PA can initiate the transformation of common organic cloud constituents like GL into highly oxygenated multifunctional compounds. These high-molecular- weight compounds that are formed in significant amount could potentially impact optical and cloud-forming properties of aerosols, especially if they partition to the aerosol surface.

CI-Orbitrap: An Analytical Instrument To Study Atmospheric Reactive Organic Species.

While acknowledged as key components in the formation of new particles in the atmosphere, the accurate characterization of gaseous (highly) oxygenated organic compounds remains challenging and requires analytical developments. Earlier studies have successfully used the nitrate ion (NO3-) based chemical ionization (CI) coupled to atmospheric pressure interface time-of-flight mass spectrometry (CI-APi-TOF) for monitoring these compounds. Despite many breakthroughs in recent years, the CI-APi-TOF has many limitations, preventing for instance the unambiguous ion identification of overlapping peaks. To tackle this analytical challenge, we developed a CI interface coupled to an ultrahigh-resolution Orbitrap mass spectrometer (CI-Orbitrap). We show that the CI-Orbitrap has similar sensitivity and selectivity as the CI-APi-TOF, but with over an order of magnitude higher mass resolving power (up to 140 000). Equally importantly, the CI-Orbitrap allows tandem mass spectrometry, providing the possibility for structural elucidation of the highly oxygenated organic molecules (HOM). As a proof of concept, we characterized HOM formed during the ozonolysis of two biogenic compounds (α-pinene and limonene), under different environmental conditions in a flow reactor. The CI-Orbitrap exhibited high sensitivity to both HOM and radical species, while easily separating ions of different elemental composition in cases where the more common TOF applications would not have been able to distinguish all ions. Our tandem mass spectrometry analyses revealed distinct fingerprint spectra for all the studied HOM. Overall, the CI-Orbitrap is an extremely promising instrument, and it provides a much-needed extension to ongoing research on HOM, with potential to impact also many other fields within atmospheric chemistry.

Characterization of oil sands naphthenic acids by negative-ion electrospray ionization mass spectrometry: Influence of acidic versus basic transfer solvent

Considerable effort and progress has been made over the past decade with respect to development of analytical tools for the determination of naphthenic acids and related components in environmental samples. However, experimental variables that influence the analytical results have not been fully explored. The relative contributions of Ox classes are of particular interest in data obtained using negative-ion electrospray ionization mass spectrometry. Using two types of ultrahigh resolution mass spectrometers (Orbitrap and FT-ICR), the apparent pH of the transfer solvent was observed to have a significant impact upon compound class distributions. A basic transfer solvent favored the detection of Ox species of lower oxygen content, while acidic pH favored the preferential observation of organic compounds with higher oxygen contents. These observed trends were independent of the instrument type. In addition, when using an acidic transfer solvent, the overall observed response was reduced by a factor of ∼20. Thus, the apparent pH of the transfer solvent has critical influence upon detection and upon the profile of different components observed within a complex mixture. In turn, this significantly impacts oil sands environmental monitoring for toxicity, forensic interpretation, and quantitation; when comparing data sets from different laboratories, these findings should therefore be taken into account.

Characterizations of HSP90-Interacting Complex in Renal Cells Using Tandem Affinity Purification and Its Potential Role in Kidney Stone Formation.

Heat shock protein 90 (HSP90) is a highly abundant molecular chaperone that interacts with many other intracellular proteins to regulate various cellular processes. However, compositions of the HSP90-interacting complex remain underinvestigated. This study thus aims to characterize such complex in human embryonic kidney (HEK293T) cells under normal physiologic state using tandem affinity purification (TAP) followed by protein identification using an ultrahigh-resolution tandem mass spectrometer (Qq-TOF MS/MS). A total of 32 proteins, including four forms of HSP90 and 16 novel HSP90-interacting partners, are successfully identified from this complex using TAP control to subtract nonspecific binders. Co-immunoprecipitation followed by immunoblotting and immunofluorescence co-staining confirms the association of HSP90 with known (HSP70, α-tubulin, and β-actin) and novel (vimentin, calpain-1, and importin-β1) partners. Knockdown of HSP90 by small-interfering RNA (siHSP90) causes significant changes in levels of HSP70, α-tubulin, β-actin, vimentin, and calpain-1, all of which are calcium oxalate (CaOx) crystal-binding proteins that play significant roles in kidney stone formation. Moreover, crystal-binding capability is significantly decreased in siHSP90-transfected cells as compared to non-transfected control and siControl-transfected cells. In summary, herein, a number of novel HSP90-interacting proteins in renal cells is reported and the potential role of HSP90-interacting complex in kidney stone formation is demonstrated.

New application of direct analysis in real time high-resolution mass spectrometry for the untargeted analysis of fresh and aged secondary organic aerosols generated from monoterpenes.

Secondary organic aerosols (SOAs) represent a significant portion of total atmospheric aerosols. They are generated by the oxidation of volatile organic compounds (VOCs), and particularly biogenic VOCs (BVOCs). The analysis of such samples is usually performed by targeted methods that often require time-consuming preparation steps that can induce loss of compounds and/or sample contaminations. Recently, untargeted methods using high-resolution mass spectrometry (HRMS) have been successfully employed for a broad characterization of chemicals in SOAs. Herein we propose a new application of the direct analysis in real time (DART) ionization method combined with HRMS to quickly detect several hundred chemicals in SOAs collected on a quartz filter without sample preparation or separation techniques. The reproducibility of measurements was good, with several hundred elemental compositions common to three different replicates. The relative standard deviations of the intensities of the chemical families ranged from 6% to 35%, with sufficient sensitivity to allow the unambiguous detection of 4 ng/mm2 of pinic acid. The presence of oligomers and specific tracers was highlighted by MSn (n ≤ 4) experiments, an achievement that is difficult to attain with other ultrahigh-resolution mass spectrometers. Contributions of this untargeted DART-HRMS method were illustrated by the analysis of fresh and aged SOAs from different gaseous precursors such as limonene, a β-pinene/limonene mixture or scots pines emissions. The results show that it is possible to use DART-HRMS for the identification of tracers of specific aging reactions, or for the identification of aerosols from specific biogenic precursors.

The secondary formation of organosulfates under interactions between biogenic emissions and anthropogenic pollutants in summer in Beijing

Abstract. Organosulfates (OSs) with ambiguous formation mechanisms are a potential source of missing secondary organic aerosol (SOA) in current atmospheric models. In this study, we chemically characterized OSs and nitrooxy-OSs (NOSs) formed under the influence of biogenic emissions and anthropogenic pollutants (e.g., NOx, SO42−) in summer in Beijing. An ultrahigh-resolution mass spectrometer equipped with an electrospray ionization source was applied to examine the overall molecular composition of S-containing organics. The number and intensities of S-containing organics, the majority of which could be assigned as OSs and NOSs, increased significantly during pollution episodes, which indicated their importance for SOA accumulation. To further investigate the distribution and formation of OSs and NOSs, high-performance liquid chromatography coupled with mass spectrometry was employed to quantify 10 OSs and 3 NOS species. The total concentrations of quantified OSs and NOSs were 41.4 and 13.8 ng m−3, respectively. Glycolic acid sulfate was the most abundant species among all the quantified species, followed by monoterpene NOSs (C10H16NO7S−). The total concentration of three isoprene OSs was 14.8 ng m−3 and the isoprene OSs formed via the HO2 channel were higher than those formed via the NO ∕ NO2 channel. The OS concentration coincided with the increase in acidic sulfate aerosols, aerosol acidity, and liquid water content (LWC), indicating the acid-catalyzed aqueous-phase formation of OSs in the presence of acidic sulfate aerosols. When sulfate dominated the accumulation of secondary inorganic aerosols (SIAs; sulfate, nitrate, and ammonium; SO42− ∕ SIA > 0.5), OS formation would obviously be promoted as the increasing of acidic sulfate aerosols, aerosol LWC, and acidity (pH < 2.8). Otherwise, acid-catalyzed OS formation would be limited by lower aerosol acidity when nitrate dominated the SIA accumulation. The nighttime enhancement of monoterpene NOSs suggested their formation via the nighttime NO3-initiated oxidation of monoterpene under high-NOx conditions. However, isoprene NOSs are presumed to form via acid-catalyzed chemistry or reactive uptake of oxidation products of isoprene. This study provides direct observational evidence and highlights the secondary formation of OSs and NOSs via the interaction between biogenic precursors and anthropogenic pollutants (NOx, SO2, and SO42−). The results imply that future reduction in anthropogenic emissions can help to reduce the biogenic SOA burden in Beijing or other areas impacted by both biogenic emissions and anthropogenic pollutants.

UHPLC-Orbitrap mass spectrometric characterization of organic aerosol from a central European city (Mainz, Germany) and a Chinese megacity (Beijing)

Fine urban aerosol particles with aerodynamic equivalent dimeter ≤2.5 μm (PM2.5) were collected in Mainz (a city within the Rhine-Main area, the third largest metropolitan region in Germany) and Beijing (Chinese megacity). A solvent mixture of acetonitrile-water was used to extract the organic aerosol fraction (OA) from the particle samples. The extracts were analyzed by an ultrahigh resolution mass spectrometer (UHRMS) Orbitrap coupled with ultra-high-performance liquid chromatography (UHPLC) both in the negative and positive ion mode. The number of compounds observed in Beijing is a factor of 2–10 higher compared to Mainz. The clear differences on chemical composition of OA in the two cities were observed. The majority of organics in Beijing OA is characterized by lower elemental H/C and O/C ratio but a higher degree of unsaturation and a larger aromaticity equivalent (XC) compared to Mainz OA, suggesting that aromatics, which are related to direct combustion compounds (e.g., oxidized polycyclic aromatic hydrocarbon (PAH)), play an important role for OA in Beijing. A significant number of organosulfates (OSs) with long-carbon chain and low degree of unsaturation were observed in Beijing OA, indicating that long-chain alkanes emitted by vehicle might be their precursors.

IMTBX and Grppr: Software for Top-Down Proteomics Utilizing Ion Mobility-Mass Spectrometry.

Top-down proteomics has emerged as a transformative method for the analysis of protein sequence and post-translational modifications (PTMs). Top-down experiments have historically been performed primarily on ultrahigh resolution mass spectrometers due to the complexity of spectra resulting from fragmentation of intact proteins, but recent advances in coupling ion mobility separations to faster, lower resolution mass analyzers now offer a viable alternative. However, software capable of interpreting the highly complex two-dimensional spectra that result from coupling ion mobility separation to top-down experiments is currently lacking. In this manuscript we present a software suite consisting of two programs, IMTBX ("IM Toolbox") and Grppr ("Grouper"), that enable fully automated processing of such data. We demonstrate the capabilities of this software suite by examining a series of intact proteins on a Waters Synapt G2 ion-mobility equipped mass spectrometer and compare the results to the manual and semiautomated data analysis procedures we have used previously.

Evaluation of toxic activities of nitrogen-containing polycyclic aromatic hydrocarbons PANH compared with their PAH analogues using in vitro cell-based bioassays

Simplification of highly complex mixtures such as crude oil by using chromatographic methods makes it possible to get more detailed information about the composition of the analyte. Separation by argentation chromatography can be achieved based on the interaction of different strength between the silver ions (Ag+) immobilized through a spacer on the silica gel surface and the π-bonds of the analytes. Heavy crude oils contain compounds with a high number of heteroatoms (N, O, S) and a high degree of unsaturation thus making them the perfect analyte for argentation chromatography. The direct coupling of argentation chromatography and ultrahigh-resolution mass spectrometry allows to continuously tracking the separation of the many different compounds by retention time and allows sensitive detection on a molecular level. Direct injection of a heavy crude oil into a ultrahigh-resolution mass spectrometer showed components with DBE of up to 25, whereas analytes with DBE of up to 35 could be detected only after separation with argentation chromatography. The reduced complexity achieved by the separation helps increasing the information depth.