Analysis of sugars and sugar polyols in atmospheric aerosols by chloride attachment in liquid chromatography/negative ion electrospray mass spectrometry

Implications of PM2.5 chemical composition in modulating microbial community dynamics during spring in Seoul

Particulate matter with an aerodynamic diameter of 2.5 μm or less (PM2.5) harbors a diverse microbial community. To assess the ecological dynamics and potential health risks associated with airborne microorganisms, it is crucial to understand the factors influencing microbial communities within PM2.5. This study investigated the influence of abiotic parameters, including air pollutants, PM2.5 chemical composition (water-soluble ions and organics), and meteorological variables, on microbial communities in PM2.5 samples collected in Seoul during the spring season. Results revealed a significant correlation between air pollutants and water-soluble ions of PM2.5 with microbial α-diversity indices. Additionally, air pollutants exerted a dominant effect on the microbial community structure, with stronger correlations observed for fungi than bacteria, whereas meteorological variables including temperature, pressure, wind speed, and humidity exerted a limited influence on fungal α-diversity. Furthermore, the results revealed specific water-soluble ions, such as SO42-, NO3-, and NH4+, as important factors influencing fungal α-diversity, whereas K+ negatively correlated with both microbial α-diversity. Moreover, PM2.5 microbial diversity was affected by organic compounds within PM2.5, with fatty acids exhibited a positive correlation with fungal diversity, while dicarboxylic acids exhibited a negative correlation with it. Furthermore, network analysis revealed direct links between air pollutants and dominant bacterial and fungal genera. The air pollutants exhibited a strong correlation with bacterial genera, such as Arthrospira and Clostridium, and fungal genera, including Aureobasidium and Cladosporium. These results will contribute to our understanding of the ecological dynamics of airborne microorganisms and provide insights into the potential risks associated with PM2.5 exposure.

Effect of salinity on molecular characterization of dissolved organic matter using ESI FT-ICR MS

Solid-phase extraction (SPE) coupled with negative-ion Electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been widely used for molecular characterization of dissolved organic matter (DOM). However, little attention has paid to test whether the salinity of the sample and the presence of chloride ions in water samples affect the molecular composition of DOM extracted by SPE (SPE-DOM). In this study, one natural organic matter standard and several natural waters were selected to investigate how salinity affects the molecular composition of SPE-DOM and the selectivity of chloride ion adducts formation with respect to the molecular structure of SPE-DOM in negative ion ESI FT-ICR MS analysis. The results show that the molecular composition of SPE-DOM varied in a sample made by different salinity; and the variation pattern of DOM composition was different among different water samples under the treatment of consistent salinity gradients. The chloride ions can't be completely removed from cartridges in conventional SPE, thus leading organic compounds in SPE-DOM to form [M+Cl]‾ adducts when performing ESI FT-ICR MS analysis. In addition, the molecules with high H/C and low O/C ratios were likely to form [M+Cl]‾ ions. The relative abundance of [M+Cl]‾ ions could increase with the increase of salinity. These results are instructive to guide the pretreatment and molecular characterization of DOM in water samples with different salinity. Overall, we proposed a modification to the SPE to minimum reduce the formation of chloride ion adducts during the isolation of DOM.

Organic aerosols in the inland Tibetan Plateau: New insights from molecular tracers

Aerosols affect the radiative forcing of the global climate and cloud properties. Organic aerosols are among the most important, yet least understood, components of the sensitive Tibetan Plateau atmosphere. Here, the concentration of and the seasonal and diurnal variations in biomass burning and biogenic aerosols, and their contribution to organic aerosols in the inland Tibetan Plateau were investigated using molecular tracers. Biomass burning tracers including levoglucosan and its isomers, and aromatic acids showed higher concentrations during winter than in summer. Molecular tracers of primary and secondary biogenic organic aerosols were more abundant during summer than those in winter. Meteorological conditions were the main factors influencing diurnal variations in most organic molecular tracers during both seasons. According to the tracer-based method, we found that biogenic secondary organic aerosols (38.5 %) and fungal spores (14.4 %) were the two dominant contributors to organic aerosols during summer, whereas biomass burning (15.4 %) was an important aerosol source during winter at remote continental background site. Results from the positive matrix factor source apportionment also demonstrate the importance of biomass burning and biogenic aerosols in the inland Tibetan Plateau. During winter, the long-range transport of biomass burning from South Asia contributes to organic aerosols. In contrast, the precursors, biogenic secondary organic aerosols, and fungal spores from local emissions/long-range transport are the major sources of organic aerosols during summer. Further investigation is required to distinguish between local emissions and the long-range transport of organic aerosols. In-depth insights into the organic aerosols in the Tibetan Plateau are expected to reduce the uncertainties when evaluating aerosol effects on the climate system in the Tibetan Plateau.

Mass Spectrometry Approach for Differentiation of Positional Isomers of Saccharides: Toward Direct Analysis of Rare Sugars

Rare sugars have gained popularity in recent years due to their use in antiaging treatments, their ability to sweeten with few calories, and their ability to heal infections. Rare sugars are found in small quantities in nature, and they exist typically as isomeric forms of traditional sugars, rendering some challenges in their isolation, synthesis, and characterization. In this work, we present the first direct mass spectrometric approach for differentiating structural isomers of sucrose that differ only by their glycosidic linkages. The method employed a noncontact nanoelectrospray (nESI) platform capable of analyzing minuscule volumes (5 μL) of saccharides via the formation of halide adducts ([M+X]-; X = Cl and Br). Tandem mass spectrometry analysis of the five structural isomers of sucrose afforded diagnostic fragment ions that can be used to distinguish each isomer. Detailed mechanisms showcasing the distinct fragmentation pattern for each isomer are discussed. The method was applied to characterize and confirm the presence of all five selected rare sugars in raw honey complex samples. Aside from the five natural α isomers of sucrose, the method was also suitable for differentiating some β isomers of the same glycosidic linkages, provided the monomeric sugar units are different. The halide adduct formation via the noncontact nESI source was also proven to be effective for oligosaccharides such as raffinose, β-cyclodextrin, and maltoheptaose. The results from this study encourage the future development of methods that function with simple operation to enable straightforward characterization of small quantities of rare sugars.

Selective extraction of levoglucosan and its isomers from complex matrices using ligand exchange-solid phase extraction for analysis by liquid chromatography-electrospray ionization-tandem mass spectrometry

The analysis of trace quantities of monosaccharide anhydrides (MAs) in sediments is complicated by the lack of fast and reliable technologies to selectively extract these water-soluble non-ionic compounds from samples of complex composition. Here we describe a solid phase extraction method that takes advantage of the affinity between monosaccharide anhydrides (MAs) and immobilized Na⁺ ions related to ligand-exchange processes (LE-SPE). The capacity factor of LE-SPE columns was enhanced by using non-aqueous mobile phases such as DCM/MeOH mixtures. We have used the unique properties of LE-SPE columns to selectively extract MAs from lacustrine, coastal, and deep-sea oceanic sediment samples. The analytical procedure produces extracts with low ion suppression effects (0-20%), resulting in ideal conditions for MAs quantification with LC-ESI-MS/MS systems irrespective of the sedimentary matrix and MAs concentration. The analytical method yields repeatable concentration values (RSD of 9-23% for levoglucosan and 15-34% for mannosan and galactosan) and an IS recovery of 45-70%. The instrumental dynamic range is 10-10000 pg injected, but in practice, the methodological lower limit of quantification is constrained by sample contamination during processing. The combination of LE-SPE and LC-ESI-MS/MS has the potential to produce sensitive and reliable technologies to analyze saccharides and amino acids in environmental and biological samples.

A Molecular Dynamic Study of the Effects of Surface Partitioning on the OH Radical Interactions with Solutes in Multicomponent Aqueous Aerosols

The surface-bulk partitioning of small saccharide and amide molecules in aqueous droplets was investigated using molecular dynamics. The air-particle interface was modeled using a 80 Å cubic water box containing a series of organic molecules and surrounded by gaseous OH radicals. The properties of the organic solutes within the interface and the water bulk were examined at a molecular level using density profiles and radial pair distribution functions. Molecules containing only polar functional groups such as urea and glucose are found predominantly in the water bulk, forming an exclusion layer near the water surface. Substitution of a single polar group by an alkyl group in sugars and amides leads to the migration of the molecule toward the interface. Within the first 2 nm from the water surface, surface-active solutes lose their rotational freedom and adopt a preferred orientation with the alkyl group pointing toward the surface. The different packing within the interface leads to different solvation shell structures and enhanced interaction between the organic molecules and absorbed OH radicals. The simulations provide quantitative information about the dimension, composition, and organization of the air-water interface as well as about the nonreactive interaction of the OH radicals with the organic solutes. It suggests that increased concentrations, preferred orientations, and decreased solvation near the air-water surface may lead to differences in reactivities between surface-active and surface-inactive molecules. The results are important to explain how heterogeneous oxidation mechanisms and kinetics within interfaces may differ from those of the bulk.

Dihydrogen phosphate anion boosts the detection of sugars in electrospray ionization mass spectrometry: A combined experimental and computational investigation

RATIONALE

Sugars are key molecules of life but challenging to detect via electrospray ionization mass spectrometry (ESI-MS). Unfortunately, sugars are challenging analytes for mass spectrometric methods due to their high gas-phase deprotonation energies and low gas-phase proton affinities which make them difficult to ionize in high abundance for MS detection.

METHODS

Hydrogen-bond interactions in H₂ PO₄ ^- -saccharide anionic systems were studied both experimentally (via electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry, ESI-FT-ICR-MS) and computationally by several sophisticated density-functional theoretical methods (DFT and DFT-D3).

RESULTS

The H₂ PO₄ ^- dopant boosts the detection of sugars up to 51-times in the case of sucrose and up to 263-times for glucose (at 0.1 ppm concentration level). H₂ PO₄ ^- binds toward sugar molecules with noticeably more hydrogen bonds than the established dopant chloride Cl^- does, with increasing binding energies in the order: Monosaccharides < Trisaccharides < Disaccharides. Analysis of a complex oak plant sample revealed that NH₄ H₂ PO₄ specifically labeled a diverse set of sugar-type plant metabolites in the form of [M + H₂ PO₄ ]^- complexes.

CONCLUSIONS

We reveal the mechanism of interaction of H₂ PO₄ ^- with different sugars and glycosylated organic compounds, which significantly enhances their ionization in mass spectrometry. A computational and experimental investigation is presented. A strong correlation between the MS signal intensities of detected [M + H₂ PO₄ ]^- anions of different saccharides and their calculated dissociation enthalpies was revealed. Thus, the variation in MS signal intensities can be very well described to a large extent by the variation in calculated saccharide affinities toward the H₂ PO₄ ^- dopant anion, showing that DFT-D3 can very well describe experimental FT-ICR-MS observations.

Saccharides in atmospheric particulate and sedimentary organic matter: Status overview and future perspectives

Saccharides are omnipresent compounds in terrestrial and marine ecosystems. Since the 2000s, their role in environmental and geochemical studies has significantly increased, but only anhydrosaccharides (mainly levoglucosan) have been reviewed. Here we present the wider knowledge about saccharides in organic matter of aerosols, bottom sediments, soils, dust, and sedimentary rocks. The main purpose here is to characterize the possible sources of saccharides, as well as sacharol formation, seasonal variability, and the possible applications in environmental and paleoenvironmental interpretations. Different saccharide sources were designated, including biomass burning, and particulate matter such as pollen, spores, lichen, and fungi, as well as polysaccharide decomposition as possible inputs of monosaccharides. The main focus was on the most common saccharides encountered in environmental samples and sedimentary rocks. These are the mono- and disaccharides glucose, fructose, sucrose, and trehalose, and sacharols arabitol and mannitol. The anhydrosaccharides levoglucosan, mannosan, and galactosan were evaluated as ancient wildfire indicators and industrialization tracers found in lacustrine sediments starting from Pleistocene to contemporary deposits. However, other anhydrosaccharides like xylosan and arabinosan were also found as products of fossil wood burning. These anhydrosaccharides have the potential to be further tracers of hemicellulose burning. Additional recommendations are proposed for future research, including environmental and paleoenvironmental topics that need to be addressed.

In-Source Microdroplet Derivatization Using Coaxial Contained-Electrospray Mass Spectrometry for Enhanced Sensitivity in Saccharide Analysis

Online, droplet-based in-source chemical derivatization is accomplished using a coaxial-flow contained-electrospray ionization (contained-ESI) source to enhance sensitivity for the mass spectrometric analysis of saccharides. Derivatization is completed in microseconds by exploiting the reaction rate acceleration afforded by electrospray microdroplets. Significant improvements in method sensitivity are realized with minimal sample preparation and few resources when compared to traditional benchtop derivatizations. For this work, the formation of easily ionizable phenylboronate ester derivatives of several mono-, di-, and oligosaccharides is achieved. Various reaction parameters including concentration and pH were evaluated, and a Design of Experiments approach was used to optimize ion source parameters. Signal enhancements of greater than two orders of magnitude were observed for many mono- and disaccharides using in-source phenylboronic acid derivatization, resulting in parts-per-trillion (picomolar) limits of detection. In addition, amino sugars such as glucosamine, which do not ionize in negative mode, were detected at low parts-per-billion concentrations, and isobaric sugars such as lactose and sucrose were easily distinguished. The new in-source derivatization approach can be employed to expand the utility of ESI-MS analysis for compounds that historically experience limited sensitivity and detectability, while avoiding resource-intensive, bulk-phase derivatization procedures.

Seeded Crystal Growth of Internally Mixed Organic-Inorganic Aerosols: Impact of Organic Phase State

Atmospheric aerosols are complex with both inorganic and organic components. The soluble inorganics can transition between aqueous and crystalline phases through efflorescence and deliquescence. This study focuses on the efflorescence of (NH₄)₂SO₄/organic particles by seeded crystal growth through contact with a crystal of (NH₄)₂SO₄. Seeded crystal growth is known to effectively shut down supersaturation of aqueous aerosols. Here, we investigate whether organics can inhibit seeded crystal growth. We demonstrate that poly(ethylene glycol) 400 (PEG-400), which phase-separates from the aqueous (NH₄)₂SO₄ and forms a core-shell structure, did not inhibit seeded crystal growth of (NH₄)₂SO₄ at all relative humidity (RH) values below deliquescence RH. The PEG-400 layer was not viscous enough to prevent the diffusion of species through the coating. In contrast, we find that although raffinose, which stays homogeneously mixed with (NH₄)₂SO₄, did not inhibit seeded crystal growth at RH > 45%, it did inhibit heterogeneous efflorescence at lower humidities. Viscosity measurements using an electrodynamic balance show a significant increase in viscosity as humidity was lowered, suggesting that inhibited diffusion of water and ions prevented efflorescence. The observed efflorescence at the higher RH also demonstrates that collisions can induce efflorescence of mixed aerosols that would otherwise not homogeneously effloresce.

Molecular Speciation of Size Fractionated Particulate Water-Soluble Organic Carbon by Two-Dimensional Nuclear Magnetic Resonance (NMR) Spectroscopy

Particulate matter is associated with increased morbidity and mortality; its effects depend on particle size and chemical content. It is important to understand the composition and resultant toxicological profile of particulate organic compounds, the largest and most complex fraction of particulate matter. The objective of the study was to delineate the nuclear magnetic resonance (NMR) spectral fingerprint of the biologically relevant water-soluble organic carbon (WSOC) fraction of size fractionated urban aerosol. A combination of one and two-dimensional NMR spectroscopy methods was used. The size distribution of particle mass, water-soluble extract, non-exchangeable organic hydrogen functional types and specific biomarkers such as levoglucosan, methane sulfonate, ammonium and saccharides indicated the contribution of fresh and aged wood burning emissions, anthropogenic and biogenic secondary aerosol for fine particles as well as primary traffic exhausts and pollen for large particles. Humic-like macromolecules in the fine particle size range included branched carbon structures containing aromatic, olefinic, keto and nitrile groups and terminal carboxylic and hydroxyl groups such as terpenoid-like polycarboxylic acids and polyols. Our study show that 2D-NMR spectroscopy can be applied to study the chemical composition of size fractionated aerosols.

PM10-Bound Sugars: Chemical Composition, Sources and Seasonal Variations

The presence of anhydrosugars and sugar alcohols in airborne articulate matter <10 µm (PM10) samples collected between December 2018 and June 2019 was studied for two urban environments in Coimbra. Anhydrosugars were used to estimate the biomass burning contribution, and sugar alcohols were investigated regarding biological sources. Anhydrosugars contributed more than sugar alcohols to the total sugars, mainly levoglucosan. Higher levoglucosan concentrations were linked with the use of biomass-fueled heating appliances, mainly during cold periods. A significant contribution from biomass burning smoke was registered, accounting for 20% to 23% of the PM10 mass in the colder period. Xylitol presented higher concentrations in the colder period and was well correlated with levoglucosan, indicating a common origin. Mannitol and arabitol were well correlated with each other but did not present any kind of correlation with anhydrosugars or xylitol, suggesting a natural source. A quantitative estimation based on the concentration of ambient tracers (mannitol) was evaluated, and the results reveal that, for the two sites, the fungal spore relative contribution to PM10 (roadside site: 2.7% to 2.8%; urban background: 1.9% to 2.7%) and OC mass (roadside site: 6.2% to 8.1%; urban background: 3.9% to 7.5%) was significant and always higher in the warmer period.

Photochemical Oxidation of Water-Soluble Organic Carbon (WSOC) on Mineral Dust and Enhanced Organic Ammonium Formation

Water-soluble organic carbon (WSOC), which is closely related to biogenic emissions, is of great importance in the atmosphere for its ubiquitous existence and rich abundance. Levoglucosan, a typical WSOC, is usually considered to be stable and thus used as a tracer of biomass burning. However, we found that levoglucosan can be photo-oxidized on mineral dust, with formic acid, oxalic acid, glyoxylic acid, 2,3-dioxopropanoic acid, dicarbonic acid, performic acid, mesoxalaldehyde, 2-hydroxymalonaldehyde, carbonic formic anhydride, and 1,3-dioxolane-2,4-dione detected as main products. Further, we observed the heterogeneous uptake of NH₃ promoted by the carboxylic acids stemming from the photocatalytic oxidation (PCO) of levoglucosan. The mineral-dust-initiated PCO of levoglucosan and enhanced heterogeneous uptake of NH₃, which are highly influenced by irradiation and moisture conditions, were for the first time revealed. The reaction mechanisms and pathways were studied in detail by diffuse reflection infrared Fourier transform spectroscopy (DRIFTS), high-pressure photon ionization time-of-flight mass spectrometry (HPPI-ToF-MS) and flow reactor systems. Diverse WSOC constituents were studied as well, and the reactivity toward NH₃ is related to the number of hydroxyl groups of the WSOC molecules. This work reveals a new precursor of secondary organic aerosols and provides experimental evidence of the existence of organic ammonium salts in atmospheric particles.

One-year characterization of organic aerosol markers in urban Beijing: Seasonal variation and spatiotemporal comparison

Organic aerosol (OA) is a major component of fine particulate matter (PM); however, only 10%-30% of OA have been identified as individual compounds, and some are used as markers to trace the sources and formation mechanisms of OA. The temporal and spatial coverage of these OA markers nonetheless remain inadequately characterized. This study presents a year-long measurement of 92 organic markers in PM_2.5 samples collected at an urban site in Beijing from 2014 to 2015. Saccharides were the most abundant (340.1 ng m^-3) species detected, followed by phthalic acids (283.4 ng m^-3). In summer, high proportions (8%-24%) of phthalic acids, n-alkanes, fatty acids, and n-alcohols indicate dominant contributions of biogenic emission and atmospheric oxidation to OA in Beijing. In winter, when anthropogenic sources prevail, saccharides, polycyclic aromatic hydrocarbons, and hopanes are more prominent (4%-25%). The spatial distributions of these OA markers in China show higher concentrations in northern cities (mainly from coal combustion and biomass burning) than in southern cities (mainly from vehicular emission). The inter-annual variations of OA markers, except for hopanes, from 2001 to 2015 suggest significant alleviation of the primary OA pollution in Beijing, with an average reduction of 35%-89% compared with those before 2008. The diagnostic ratio analyses between OA markers indicate that contributions from coal combustion and biomass burning decreased, whereas those from vehicular emission increased. Increasingly large vehicle fleets have increased hopane concentrations since 2008, but the levels were 35% lower in 2015 than those in 2010-2011 because of the tightening of emission controls for vehicles. This study provides a long-term and geographical comparison (from Beijing to other locations in China and beyond) of OA markers, demonstrating the temporal and spatial variations in primary OA, and calls for more studies on secondary OA.

Molecular characteristics of organic compositions in fresh and aged biomass burning aerosols

Biomass burning (BB) is the most important source of primary organic aerosols (OA) in the atmosphere that has significant impact on local/regional air quality and human health. However, few studies paid attention to the evolution of molecular characteristics of BB OA in the atmospheric aging processes. In this study, both fresh and aged PM_2.5 aerosols from burning of rice, maize, and wheat straws were collected from a combined system of combustion chamber and oxidation flow reactor, and were analyzed for >100 organic species. The emission factors (EFs) of anhydrosugars and some fatty acids showed slight variations between fresh and aged samples, indicating that these compounds are relatively stable. However, the EFs of n-alkanes, fatty alcohols, and parent-PAHs decreased 8-57% from fresh to aged samples, suggesting that they can undergo further oxidation to form other organic materials in the atmosphere. Phthalic acids, nitrophenols and isoprene-derived products were mainly secondarily formed by aging processes. Thus their EFs increased by 2-23 times from fresh to aged samples. Levoglucosan was the most abundant individual organic tracer, and its EF varied slightly between fresh and aged samples, proving its indicative role on BB emission. Moreover, the ratio of vanillic acid to levoglucosan and p-hydroxybenzoic acid to levoglucosan increased 2-13 times from fresh to aged samples. Therefore they can be used to investigate the impact of aging processes on BB aerosols in the atmosphere. RO₂ + HO₂ pathway derived 2-methyltetrols (2-MTs) predominated the EFs of isoprene-derived products (SOA_i) in the fresh samples. However, RO₂ + NO pathway derived 2-methylglyceric acid (2-MGA) increased by >30 times and became comparable with 2-MTs in aged particles. The ratio of 2-MGA/2-MTs increased from 0.06-0.27 in fresh samples to 0.94-1.18 in aged samples, because the high loading of NO_x in BB smoke enhanced the formation of SOA_i through RO₂ + NO reactions.

Validation of a sensitive high performance liquid chromatography tandem mass spectrometric method for measuring carbohydrates in aerosol samples

Carbohydrates (such as levoglucosan) are a class of important water-soluble organic compounds in atmosphere. In this study, a high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) was applied to characterize carbohydrates in aerosol particles. Since carbohydrate was a kind of compound with low response in mass spectrometry, the conventional HPLC-MS/MS method was not sensitive enough to determine it. When acetate acid was added into mobile phase as buffer, the transition of [M+CH₃COO]^-→[M-H]^- could be selected as the quantification ions. In the range from 1.0 μg L^-1 to 20 μg mL^-1, the coefficients of regression (r²) were more than 0.990, and relative standard deviations (RSD) for replicated injections were lower than 2%. The limit of detection (LOD) and quantification (LOQ) were lower than 2.5 ng L^-1 and 10 ng L^-1, respectively. The precision and accuracy were examined by spiked samples at three different concentration levels (10 μg L^-1, 100 μg L^-1, and 500 μg L^-1) in five replicates. Recovery ratios ranged from 85% to 115% with RSD lower than 16%. Matrix effects of different carbohydrates ranged from 62% to 120%. The most sensitive HPLC-MS/MS method was developed and validated to analyze 40 aerosol samples successfully. The carbohydrates including three sugar alcohols (threitol, arabitol and sorbitol), one monosaccharide sugar (inositol), two disaccharides (sucrose, trehalose), one anhydrosugar (levoglucosan) and one 2-methyltetrols (2-Methylbutane-1,2,3,4-tretraol) were successfully quantified.

Acidic seawater improved 5-hydroxymethylfurfural yield from sugarcane bagasse under microwave hydrothermal liquefaction

5-Hydroxymethylfurfural (HMF) as value-added platform chemical can be derived from biomass. This study used microwave hydrothermal liquefaction (MHTL) to obtain HMF from sugarcane bagasse in acidic seawater conditions. The key processing parameters including temperature, reaction time, and liquid-to-solid ratio (L/S) were evaluated and optimized. The highest HMF yield of 8.1 wt% was obtained at 149 °C with a reaction time of 4 min and a L/S value of 12:1, respectively. This yield is considerable and even higher than the yield derived from sugarcane molasses under similar microwave conditions in the absence of seawater. Hence, acidic seawater was found to promote the hydrolysis of sugarcane bagasse to give HMF precursor (i.e. fructose and glucose), while simultaneously inhibiting the conversion of HMF to levulinic acid under MHTL conditions, possibly explaining the high HMF yield. This method presents a new and sustainable means of transforming waste biomass to valuable substances using seawater or brine wastewater.

Composition and source apportionment of saccharides in aerosol particles from an agro-industrial zone in the Indo-Gangetic Plain

The characterization of saccharidic compounds in atmospheric aerosols is important in order to retrieve information about organic carbon sources and their transport pathways through the atmosphere. In this study, composition and sources of saccharides in PM₁₀ were determined in a South Asian megacity (Faisalabad) during the year 2015 - 2016. PM₁₀ sampled on quartz filters was analyzed by anion exchange chromatography for the selected saccharidic compounds. The average PM₁₀ concentration was found to be 744 ± 392 μg m^-3, exceeding the daily limits proposed by Pak-EPA (150 μg m^-3), US-EPA (150 μg m^-3), and WHO (50 μg m^-3). The average total saccharidic concentration was found to be 2820 ± 2247 ng m^-3. Among the different saccharidic categories, anhydrosugars were the most abundant in concentration followed by primary sugars and sugar alcohols. The correlation and principal component analysis indicated emissions from biomass combustion, soil suspensions from areas such as farmlands having high microorganism activity, and biogenic emissions such as airborne fungal spores and vegetation detritus as major sources of saccharides in the aerosol samples.

Analysis of levoglucosan and its isomers in atmospheric samples by ion chromatography with electrospray lithium cationisation - Triple quadrupole tandem mass spectrometry

Biomass burning (BB) emissions are a significant source of particles to the atmosphere, especially in the Southern Hemisphere, where the occurrence of anthropogenic and natural wild fires is common. These emissions can threaten human health through increased exposure, whilst simultaneously representing a significant source of trace metals and nutrients to the ocean. One well known method to track BB emissions is through monitoring the atmospheric concentration of specific monosaccharide anhydrides (MAs), specifically levoglucosan and its isomers, mannosan and galactosan. Herein, a new method for the determination of levoglucosan and its isomers in marine and terrestrial aerosol samples is presented, which delivers both high selectivity and sensitivity, through the coupling of ion chromatography and triple quadrupole tandem mass spectrometry. Optimal chromatographic conditions, providing baseline separation for target anhydrosugars in under 8 min, were obtained using a Dionex CarboPac^Ⓡ PA-1 column with an electrolytically generated KOH gradient. To improve the ionisation efficiency for MS detection, an organic make-up solvent was fed into the IC column effluent before the ESI source, and to further increase both sensitivity and selectivity, cationisation of levoglucosan was investigated by adding salts into the make-up solvent, namely, sodium, ammonium and lithium salts. Using positive lithium cationisation with 0.5 mM lithium chloride in methanol as the make-up solvent, delivered at a flow rate of 0.02 mL min^-1, the levoglucosan response was improved by factors of 100 and 10, comparing to negative ionisation and positive sodium cationisation, respectively. Detection was carried out in SRM mode for quantitation and identification, achieving an instrumental LOD of 0.10, 0.12 and 0.5 µg L^-1 for levoglucosan, mannosan and galactosan, respectively. Finally, the method was applied to the analysis of 41 marine and terrestrial aerosol samples from Australia, its surrounding coastal waters and areas within the remote Southern Ocean, covering a large range of BB marker concentrations.

Effect of surface-bulk partitioning on the heterogeneous oxidation of aqueous saccharide aerosols

The OH-initiated heterogeneous oxidation of mixed saccharide aqueous aerosols is investigated using an atmospheric-pressure flow tube coupled to off-line analysis of the particle composition. For equimolar monosaccharide/disaccharide aqueous aerosol mixtures, the decay of the disaccharide is found to be significantly slower than that of the monosaccharide. Molecular dynamics simulations of the mixed aqueous solutions reveal the formation of a ∼10 Å disaccharide exclusion layer below the water surface. A simple chemical model is developed to discuss the possible effect of the disaccharide surface partitioning on the heterogeneous kinetics. The observed decays are consistent with a poor spatial overlap of the OH radical at the interface with the disaccharide in the particle bulk. The effect of partitioning on the heterogeneous oxidation of atmospheric organic aerosols is discussed.

Validation of a HILIC/ESI-MS/MS method for the wood burning marker levoglucosan and its isomers in airborne particulate matter

In the present study, a methodology involving hydrophilic interaction liquid chromatography (HILIC) and electrospray (ESI) tandem mass spectrometry (MS/MS) was developed for measurement of anhydrous monosaccharides as markers for wood burning in atmospheric aerosols, PM₁₀. No extensive sample preparation, other than ultrasound-assisted solvent extraction and evaporation, was applied. A pentahydroxysilica column enabled separation of levoglucosan from mannosan and galactosan within 5 min and the quantitative performance was validated using the standard reference materials (SRM) 1649a and 1649b. The experimentally obtained results for SRMs were in agreement with values previously reported in other studies. Achieved instrumental limits of detection (LODs) were below 10 pg injected on column, corresponding to LODs in air lower than 0.10 ng/m³ for all measured isomers for 2-3 day sampling with 1.0 m^-3 h^-1 sampling rate. The validated method was used for the determination of levoglucosan and its isomers in atmospheric aerosols collected in three different Swedish urban areas during the winter and summer time in 2017. The total measured concentrations for levoglucosan and galactosan + mannosan were determined to be between 78 and 167 ng/m³ in January 2017, which is approximately 10-times higher compared to the levels detected in July, reflecting the higher frequency of wood burning for heating during the cold season. Calculated concentration ratios between levoglucosan and its isomers in the urban area samples indicated mostly mixed softwood/hardwood combustion in winter time; on the other hand, softwood burning was observed as the major emission in summer time.

Effects of solvent parameters on the electrospray ionization tandem mass spectrometry response of glucose

RATIONALE

The importance of saccharides, the most abundant biomolecules on Earth, extends beyond their biological roles and to consumer products and industrial processes. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) is an attractive tool for the analysis of underivatized saccharides (US), but they tend to have relatively low sensitivities due to their low surface activities and lack of easily protonable or deprotonable chemical groups. An understanding of the influences that solvent parameters have on their signal intensities would enhance the usefulness of ESI-MS/MS for their analysis.

METHODS

Solutions of glucose, a model analyte for US, in various combinations of solvent, additive, additive concentration, and pH were analyzed by flow injection analysis ESI-MS/MS in both the positive and negative ionization mode. The blank-corrected signal intensities of the solvent parameter combinations were then compared.

RESULTS

The addition of acetonitrile led to severe ionization suppression in the positive ionization mode through its competition with glucose for cation adduction. High signal intensity was achieved under wide pH and concentration ranges for methanol: water solutions containing ammonium trifluoroacetate in the positive ionization mode. The highest signal intensities for acetonitrile: water solutions were those containing ammonium formate or lithium fluoride in the negative ionization mode.

CONCLUSIONS

An understanding of the influence of solvent parameters on the signal intensity of a given analyte is useful for guiding the selection process of mobile phases/flow solvents that lead to low limits of detection or the minimization of matrix effects by allowing its detection at high dilution factors.

Review of levoglucosan in glacier snow and ice studies: Recent progress and future perspectives

Levoglucosan (LEV) in glacier snow and ice layers provides a fingerprint of fire activity, ranging from modern air pollution to ancient fire emissions. In this study, we review recent progress in our understanding and application of LEV in glaciers, including analytical methods, transport and post-depositional processes, and historical records. We firstly summarize progress in analytical methods for determination of LEV in glacier snow and ice. Then, we discuss the processes influencing the records of LEV in snow and ice layers. Finally, we make some recommendations for future work, such as assessing the stability of LEV and obtaining continuous records, to increase reliability of the reconstructed ancient fire activity. This review provides an update for researchers working with LEV and will facilitate the further use of LEV as a biomarker in paleo-fire studies based on ice core records.

Simultaneous measurement of multiple organic tracers in fine aerosols from biomass burning and fungal spores by HPLC-MS/MS

Three monosaccharide anhydrides (MAs: levoglucosan, mannosan, and galactosan) and sugar alcohols (arabitol and mannitol) are widely used as organic tracers for source identification of aerosols emitted from biomass burning and fungal spores, respectively. In the past, these two types of organic tracer have been measured separately or conjointly using different analytical techniques, with which a number of disadvantages have been experienced during the application to environmental aerosol samples, including organic solvent involved extraction, time-consuming derivatization, or poor separation efficiency due to overlapping peaks, etc. Hence, in this study a more environment-friendly, effective and integrated extraction and analytical method has been developed for simultaneous determination of the above mentioned organic tracers in the same aerosol sample using ultrasonication and high performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS). The ultrasonication assisted extraction process using ultrapure water can achieve satisfactory recoveries in the range of 100.3 ± 1.3% to 108.4 ± 1.6% for these tracers. All the parameters related to LC and MS/MS have been optimized to ensure good identification and pronounced intensity for each compound. A series of rigorous validation steps have been conducted. This newly developed analytical method using ultrasonication and HPLC-MS/MS has been successfully applied to environmental aerosol samples of different pollution levels for the simultaneous measurement of the above mentioned five organic tracers from biomass burning and fungal spores.

Five organic tracers in fine aerosols can be simultaneously analysed by coupling ultrasonication and HPLC-MS/MS without a derivatization process.

Determination of glycerol in oils and fats using liquid chromatography chloride attachment electrospray ionization mass spectrometry

Existing liquid chromatography - mass spectrometry method for the analysis of short chain carboxylic acids was expanded and validated to cover also the measurement of glycerol from oils and fats. The method employs chloride anion attachment and two ions, [glycerol+³⁵Cl]^- and [glycerol+³⁷Cl]^-, as alternative quantifiers for improved selectivity of glycerol measurement. The averaged within run precision, between run precision and accuracy ranged between 0.3-7%, 0.4-6% and 94-99%, respectively, depending on the analyte ion and sample matrix. Selected renewable diesel feedstocks were analyzed with the method.

Hydrophilic interaction chromatography with Fourier transform mass spectrometry of monosaccharide anhydrides

A fast, selective, and sensitive method for the determination of three monosaccharide anhydrides (galactosan, mannosan, levoglucosan), based on hydrophilic interaction chromatography and Fourier transform mass spectrometry, was successfully developed. The simple experimental stationary phase and mass spectrometry performance screening allowed the selection of the best available chromatographic and mass spectrometry conditions. Thus, the chromatographic separation was performed on a highly selective stationary phase containing a zwitterionic phosphorylcholine group and the monosaccharide anhydrides were detected as [M+HCOO]^- adduct in the negative mode. The method showed accuracy in the range of 84-111 and 89-102% with interbatch precision expressed as relative standard deviations of 5.6-15.4 and 5.0-9.0% for the aerosol extract and snow samples, respectively. The limit of quantification in absolute values ranged from 10 to 30 pg, the limit of quantification, expressed as concentration, ranged was 0.3-0.9 ng/m³ for aerosol and 10-20 ng/mL for snow samples. The method was successfully applied for the determination of monosaccharide anhydrides in aerosol and snow samples.

Seasonal variations and source estimation of saccharides in atmospheric particulate matter in Beijing, China

Saccharides are important constituents of atmospheric particulate matter (PM). In order to better understand the sources and seasonal variations of saccharides in aerosols in Beijing, China, saccharide composition was measured in ambient PM samples collected at an urban site in Beijing. The highest concentrations of total saccharides in Beijing were observed in autumn, while an episode with abnormal high total saccharide levels was observed from 15 to 23 June, 2011, due to extensive agricultural residue burning in northern China during the wheat harvest season. Compared to the other two categories of saccharides, sugars and sugar alcohols, anhydrosugars were the predominant saccharide group, indicating that biomass burning contributions to Beijing urban aerosol were significant. Ambient sugar and sugar alcohol levels in summer and autumn were higher than those in spring and winter, while they were more abundant in PM2.5 during winter time. Levoglucosan was the most abundant saccharide compound in both PM2.5 and PM10, the annual contributions of which to total measured saccharides in PM2.5 and PM10 were 61.5% and 54.1%, respectively. To further investigate the sources of the saccharides in ambient aerosols in Beijing, the PM10 datasets were subjected to positive matrix factorization (PMF) analysis. Based on the objective function to be minimized and the interpretable factors identified by PMF, six factors appeared to be optimal as to the probable origin of saccharides in the atmosphere in Beijing, including biomass burning, soil or dust, isoprene SOA and the direct release of airborne fungal spores and pollen.

Hygroscopicity of Mixed Glycerol/Mg(NO3)2/Water Droplets Affected by the Interaction between Magnesium Ions and Glycerol Molecules

Tropospheric aerosols are usually complex mixtures of inorganic and organic components, which can influence the hygroscopicities of each other. In this research, we applied confocal Raman technology combined with optical microscopy to investigate the relationship between the hygroscopic behavior and the molecular interactions of mixed glycerol/Mg(NO3)2/water droplets. Raman spectra provide detailed structural information about the interactions between glycerol molecules and Mg(2+) ions, as well as information about the interactions between glycerol and NO3(-) ions through electrostatic interaction and hydrogen bonding. The change of the CH2 stretching band of glycerol molecules in mixed droplets suggests that the backbone structures of glycerol mainly transform from αα to γγ in the dehumidifying process, and the additional Mg(2+) ions strongly influence the structure of glycerol molecules. Because the existence of glycerol suppresses the crystallization of Mg(NO3)2·6H2O in the dehumidifying process, Mg(NO3)2 molecules in mixed droplets form an amorphous state rather than forming crystals of Mg(NO3)2·6H2O when the relative humidity is lower than 17.8%. Moreover, in mixed droplets, the molar ratio of NO3(-) to glycerol is higher in the center than in the outer region.

Molecular markers in ambient aerosol in the Mahanadi Riverside Basin of eastern central India during winter

Organic molecular markers are important atmospheric constituents. Their formation and sources are important aspects of the study of urban and rural air quality. We collected PM10 aerosol samples from the Mahanadi Riverside Basin (MRB), a rural part of eastern central India, during the winter of 2011. PM10 aerosols were characterized for molecular markers using ion chromatography. The concentration of PM10 ranged from 208.8 to 588.3 μg m(-3) with a mean concentration of 388.9 μg m(-3). Total concentration of anhydrosugars, sugar alcohols, primary sugars, and oxalate were found to be 3.25, 5.60, 10.52, and 0.37 μg m(-3), respectively, during the study period. Glucose was the most abundant species followed by levoglucosan and mannitol. Significant positive correlation between the molecular markers, anhydrosugars, sugar alcohols, primary sugars, and oxalic acid confirmed that biomass burning, biogenic activity, and re-suspension of soil particles were the main sources of aerosol in the eastern central India study area.

Attachment of chloride anion to sugars: mechanistic investigation and discovery of a new dopant for efficient sugar ionization/detection in mass spectrometers

A new method for efficient ionization of sugars in the negative-ion mode of electrospray mass spectrometry is presented. Instead of using strongly hydrophobic dopants such as dichloromethane or chloroform, efficient ionization of sugars has been achieved by using aqueous HCl solution for the first time. This methodology makes it possible to use hydrophilic dopants, which are more appropriate for chromatographic separation techniques with efficient sugar ionization and detection in mass spectrometry. The interaction between chloride anions and monosaccharides (glucose and galactose) was studied by DFT in the gas phase and by implementing the polarizable continuum model (PCM) for calculations in solution at the high B3LYP/6-31+G(d,p)//B3LYP/6-311+G(2d,p) level of theory. In all optimized geometries of identified [M+Cl](-) anions, a non-covalent interaction exists. Differences were revealed between monodentate and bidentate complex anions, with the latter having noticeably higher binding energies. The calculated affinity of glucose and galactose toward the chloride anion in the gas phase and their chloride anion binding energies in solution are in excellent agreement with glucose and galactose [M+Cl](-) experimental intensity profiles that are represented as a function of the chloride ion concentration. Density functional calculations of gas-phase affinities toward chloride anion were also performed for the studied disaccharides sucrose and gentiobiose. All calculations are in excellent agreement with the experimental data. An example is introduced wherein HCl was used to effectively ionize sugars and form chlorinated adduct anions to detect sugars and glycosylated metabolites (anthocyanins) in real biological systems (Vitis vinifera grape extracts and wines), whereas they would not have been easily detectable under standard infusion electrospray mass spectrometry conditions as deprotonated species.

Observation of elevated fungal tracers due to biomass burning in the Sichuan Basin at Chengdu City, China

Fungal material (i.e., spores and fragments) is an important component of atmospheric aerosols. In order to examine the variability of fungal abundance in fine particles (PM(2.5)) during a biomass burning season, an intensive measurement campaign was conducted in the Sichuan Basin at Chengdu, a megacity in southwest China, in spring 2009. The aerosol samples were analyzed for carbonaceous species, including molecular tracers for biomass burning and fungal material, and water soluble ions. The results were interpreted with the help of principle component analysis, fire count maps, and the WRF model. Elevated concentrations of arabitol and mannitol were found with average concentrations of 21.5±16.6 ng m(-3) and 43.9±19.3 ng m(-3), respectively, which were unexpectedly higher than those measured in fine particles in any other study reported previously. Even higher concentrations were observed in cases with simultaneous enhancements in the biomass burning tracers levoglucosan and K(+). In the case of influence by pollution plumes from biomass burning regions, the fungal tracer concentrations reached maximum values of 79.6 ng m(-3) and 121.8 ng m(-3), coinciding with peak levels of levoglucosan and K(+). Statistically significant correlations were found between the simultaneously observed fungal tracers (arabitol and mannitol) and biomass burning tracers (levoglucosan and K(+)), suggesting that these species were emitted by co-located sources, and hence the elevated fungal tracers were likely associated with biomass burning activities.

Biomass burning contributions to urban aerosols in a coastal Mediterranean city

Mean annual biomass burning contributions to the bulk particulate matter (PM(X)) load were quantified in a southern-European urban environment (Barcelona, Spain) with special attention to typical Mediterranean winter and summer conditions. In spite of the complexity of the local air pollution cocktail and the expected low contribution of biomass burning emissions to PM levels in Southern Europe, the impact of these emissions was detected at an urban background site by means of tracers such as levoglucosan, K(+) and organic carbon (OC). The significant correlation between levoglucosan and OC (r(2)=0.77) and K(+) (r(2)=0.65), as well as a marked day/night variability of the levoglucosan levels and levoglucosan/OC ratios was indicative of the contribution from regional scale biomass burning emissions during night-time transported by land breezes. In addition, on specific days (21-22 March), the contribution from long-range transported biomass burning aerosols was detected. Quantification of the contribution of biomass burning aerosols to PM levels on an annual basis was possible by means of the Multilinear Engine (ME). Biomass burning emissions accounted for 3% of PM(10) and PM(2.5) (annual mean), while this percentage increased up to 5% of PM(1). During the winter period, regional-scale biomass burning emissions (agricultural waste burning) were estimated to contribute with 7±4% of PM(2.5) aerosols during night-time (period when emissions were clearly detected). Long-range transported biomass burning aerosols (possibly from forest fires and/or agricultural waste burning) accounted for 5±2% of PM(2.5) during specific episodes. Annually, biomass burning emissions accounted for 19%-21% of OC levels in PM(10), PM(2.5) and PM(1). The contribution of this source to K(+) ranged between 48% for PM(10) and 97% for PM(1) (annual mean). Results for K(+) from biomass burning evidenced that this tracer is mostly emitted in the fine fraction, and thus coarse K(+) could not be taken as an appropriate tracer of biomass burning.

Mass spectrometry of atmospheric aerosols--recent developments and applications. Part I: Off-line mass spectrometry techniques

Many of the significant advances in our understanding of atmospheric particles can be attributed to the application of mass spectrometry. Mass spectrometry provides high sensitivity with a fast response time to probe chemically complex particles. This review focuses on recent developments and applications in the field of mass spectrometry of atmospheric aerosols. In Part I of this two-part review, we concentrate on off-line mass spectrometry techniques, which require sample collection on filters but can provide detailed molecular speciation. In particular, off-line mass spectrometry techniques utilizing tandem mass spectrometry experiments and high resolution mass analyzers provide improved insight into secondary organic aerosol formation and heterogeneous reaction pathways through detailed structural elucidation at the molecular level.

Dereplication of microbial natural products by LC-DAD-TOFMS

Dereplication, the rapid identification of known compounds present in a mixture, is crucial to the fast discovery of novel natural products. Determining the elemental composition of compounds in mixtures and tentatively identifying natural products using MS/MS and UV/vis spectra is becoming easier with advances in analytical equipment and better compound databases. Here we demonstrate the use of LC-UV/vis-MS-based dereplication using data from UV/vis diode array detection and ESI+/ESI- time-of-flight MS for assignment of 719 microbial natural product and mycotoxin reference standards. ESI+ was the most versatile ionization method, detecting 93% of the compounds, although with 12% ionizing poorly. Using ESI+ alone, 56.1% of the compounds could be unambiguously assigned based on characteristic patterns of multiple adduct ions. Using ESI-, 36.4% of the compounds could have their molecular mass assigned unambiguously using multiple adduct ions, while a further 41% of the compounds were detected only as [M - H]-. The most reliable interpretations of conflicting ESI+ and ESI- data on a chromatographic peak were from the ionization polarity with the most intense ionization. Poor ionization was most common with small molecules (<200 Da). In ESI-, these were often polar and basic, while in ESI+ they were small aromatic acids or anthraquinones. No single ion-source settings could be applied over a m/z 60-2000 range. However, continuous switching among three settings (e.g., for 0.5 s each) during the chromatographic run allowed MS of both small labile molecules and large peptides, and pseudo MS/MS data on labile molecules since the settings for large molecules often induce fragmentation into small molecules.

Microbial and bioconversion production of D-xylitol and its detection and application

D-Xylitol is found in low content as a natural constituent of many fruits and vegetables. It is a five-carbon sugar polyol and has been used as a food additive and sweetening agent to replace sucrose, especially for non-insulin dependent diabetics. It has multiple beneficial health effects, such as the prevention of dental caries, and acute otitis media. In industry, it has been produced by chemical reduction of D-xylose mainly from photosynthetic biomass hydrolysates. As an alternative method of chemical reduction, biosynthesis of D-xylitol has been focused on the metabolically engineered Saccharomyces cerevisiae and Candida strains. In order to detect D-xylitol in the production processes, several detection methods have been established, such as gas chromatography (GC)-based methods, high performance liquid chromatography (HPLC)-based methods, LC-MS methods, and capillary electrophoresis methods (CE). The advantages and disadvantages of these methods are compared in this review.

Identification and quantification of the osmodiuretic mannitol in urine for sports drug testing using gas chromatography-mass spectrometry

The osmodiuretic mannitol can be potentially misused in sports, owing to its urine diluting effect and the possibility to decrease bodyweight. To reveal a doping offence, resulting urinary mannitol concentrations after a prohibited intravenous application and a permitted oral intake have to be differentiated. Therefore, a reliable gas chromatography-mass spectrometry (GC-MS) method was established based on peracetyl derivatives of the analytes. All possible hexitols (allitol, galactitol, iditol, altritols, sorbitol and mannitol) that can occur in human urine were separated and identified on a phenyl-methylpolysiloxane column (HP-5MS) within 10.75 min, and the method demonstrated its capability for quantification purposes. The lower limit of detection and lower limit of quantification were estimated at 0.9 microg mL(-1) and 2.4 microg mL(-1), respectively, and the assay was validated for mannitol and sorbitol regarding the parameters specificity, linearity, intra- (<10%) and inter-day precision (<15%) and accuracy (92-102%). To investigate urinary mannitol concentrations after oral intake the method was applied to an excretion study, providing a mean urinary excretion of mannitol of 19.5%. Comparison of theoretically expected urinary levels after a common therapeutic dose of mannitol and preliminary results on physiological urinary mannitol levels were promising, regarding a threshold level for mannitol that can be utilised for doping control purposes.