Fourier Transform Ion Cyclotron Resonance Research Articles

Groundwater-derived carbon stimulates headwater stream CO2 emission potential on the Qinghai-Tibet Plateau

CO2 emissions from headwater streams are a crucial component of greenhouse gas flux in inland waters. However, the influence of groundwater, a major contributor to streams in the Asian Water Tower (Qinghai-Tibet Plateau, QTP), on CO2 levels remains unclear. This study employed stable isotope analysis and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to demonstrate that groundwater-derived dissolved inorganic carbon (DIC) significantly enhances CO2 supersaturation in the Shuiluo stream on the QTP. Specifically, the partial pressure of CO2 (pCO2), indicative of CO2 emission potential, increased more than threefold to 1,615 ± 495 μatm in groundwater-rich sites, nearly one time higher than the mean value (843 μatm) across the QTP. Groundwater-derived carbonate weathering had a significant impact of 76.6% on the increased pCO2, whereas the degradation of highly unsaturated polyphenolics with high O/C contributed to a decrease of 15.8%. The estimated inflow of groundwater-derived DIC could reach 9.59 ± 0.34 Tg C/y in total runoff across the QTP, highlighting significant CO2 sources. This study presents new findings on the effects of groundwater-derived DIC on stream CO2 emissions in weathered regions and expands our knowledge of fluvial CO2 emission on the QTP.

Differential interaction modes of As(III)/As(V) with microbial cell membrane induces opposite effects on organic contaminant biodegradation in groundwater

Arsenic, a widespread toxic metalloid in groundwater, derives both from natural geological environment and industrial discharge, is extensively detected to be coexisting with organic contaminants, such as 2,4,6-trichlorophenol (TCP), a prior concerned pollutant. During biological remediation of groundwater, arsenic potentially intervenes microbial behaviors. This study found an opposite interference of arsenic in its two different valences (III and V) on the degradation of TCP by the functional bacteria, Sphingomonas fennica K101. As(III) inhibited TCP degradation in a concentration-dependent manner (from 0.1-10 mg/L), with a maximum inhibition rate of 35.5 %, whereas As(V) exhibited promoting effects by 13.8 % and 33.2 % at 1 mg/L and 10 mg/L, respectively. Employing field emission transmission electron microscopy, quantum chemical calculation, fourier-transform ion cyclotron resonance mass spectrometry and metabolomic analysis, we unveil distinct interactions between cell membranes and arsenic in two valence states. Exposure to As(III) led to significant accumulation of As(III) in the cytoplasm, followed by interaction with intracellular ferritin (ferritin heavy chain 1), releasing iron ions and generating ROS. Subsequently, it induced ferroptosis and disrupted bacterial basal metabolism, thereby inhibiting TCP biodegradation. Oppositely, As(V) bound to a critical component sphingosine and triggered sphingosine polymerization, increasing membrane permeability, which was evidenced by measuring lactate dehydrogenase release. This process facilitated TCP transmembrane permeation by reducing membrane or extracellular secretion resistance. As(V) concurrently upregulated energy metabolism and accelerated TCP degradation. Our study elucidates the influence of prevalent arsenic on biodegradation efficacy, particularly amidst changing redox conditions associated with varying arsenic valences.

Molecular insights into pilot-scale selective removal of emerging contaminants in hospital wastewater

Advanced oxidation processes (AOPs) are a promising technology for removing emerging organic contaminants (EOCs) from wastewater, while the coexisting dissolved organic matter (DOM) significantly hinders effective oxidative removal of EOCs. Understanding the effects of DOM on EOCs removal in real water matrices is crucial for designing more efficient AOPs. Herein, a pilot-scale integrated in-situ ozonation/ultrafiltration process was conducted to remove EOCs from hospital wastewater. Furthermore, the ozonation reactivity of DOM and EOCs was contrastingly analyzed at the molecular level. Our integrated process selectively removed 85 % of EOCs at a relatively low oxidant dosage of 0.44 mg O3 per mg dissolved organic carbon (DOC). Using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), we reveal that ozone selectivity for EOCs arose from their overall reductive characteristics of being more aromatic and unsaturated in molecular composition compared to DOM. Additionally, specific DOM compounds potentially facilitate EOCs removal. This work provides pilot-scale experience in EOCs removal from hospital wastewater and in-depth understanding of DOM’s role in the integrated process, guiding the development of effective AOPs for selective removal of emerging contaminants.

Mass Spectrometry–Based Proteomics for the Masses: Peptide and Protein Identification in the Hunt Laboratory During the 2000’s

There has been a rapid increase in the number of individuals utilizing mass spectrometry (MS)-based proteomics to study complex biological systems and questions since the start of the 2000's. Building off the advancements in ionization and liquid chromatography scientists continued to push towards technology that would enable in-depth analysis of biological specimen. Donald F Hunt and the Hunt laboratory were major contributors to this effort with their work on improving upon existing Fourier Transform MS, development of electron transfer dissociation, and continued work on ion-ion reactions to improve intact protein analysis. Collaboration with other instrumentation laboratories and instrument companies led to the sharing of technology and eventual commercialization providing greater access. Additionally, the Hunt laboratory spread the gospel of mass spectrometry-based proteomics through collaborations that lasted decades with other scientists who were experts in immunology, cellular signaling, epigenetics, and other fascinating fields. This article attempts to highlight the many contributions of Don and the Hunt laboratory to peptide and protein identification since the year 2000.

EDDS application destabilizes soil organic matter in phytoremediation: Insights from quantity and molecular composition of dissolved organic matter

The stability of soil organic matter (SOM) is crucial for metal transport and carbon cycling. S,S-ethylenediaminedisuccinic acid (EDDS) is widely used to enhance phytoremediation efficiency for heavy metals in contaminated soils, yet its specific impacts on SOM have been underexplored. This study investigates the effects of EDDS on SOM stability using a rhizobox experiment with ryegrass. Changes in soil dissolved organic matter (DOM) quantity and molecular composition were analyzed via Fourier transform ion cyclotron resonance mass spectrometry. Results showed that the use of EDDS increased the uptake of Cu, Cd and Pb by ryegrass, but simultaneously induced the destabilization and transformation of SOM. After 7 days of EDDS application, dissolved organic carbon (DOC) and nitrogen (DON) concentrations in rhizosphere soils increased significantly by 3.44 and 10.2 times, respectively. In addition, EDDS reduced lipids (56.3%) and proteins/amino sugars-like compounds (52.1%), while increasing tannins (9.11%) and condensed aromatics-like compounds (24.4%) in the rhizosphere DOM. These effects likely stem from EDDS's dual action: extracting Fe/Al from SOM-mineral aggregates, releasing SOM into the DOM pool, and promoting microbial degradation of bioavailable carbon through chain scission and dehydration. Our study firstly revealed that the application of EDDS in phytoremediation increased the mineralization of SOM and release of CO2 from soil to the atmosphere, which is important to assess the carbon budget of phytoremediation and develop climate-smart strategy in future.

Treatment of sludge hydrothermal carbonization wastewater by ferrous/sodium percarbonate system: Effect of wastewater composition and role of coagulation and oxidation

It is crucial to explore the effect of complex wastewater compositions on the ferrous/sodium percarbonate (Fe(Ⅱ)/SPC) system and the role of oxidation-coagulation in designing water treatment processes. This study employed redundancy analysis to investigate the effects of wastewater constituents on oxidation and coagulation. Raman analysis, X-ray Photoelectron Spectroscopy, and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry were used to determine the roles of oxidation and coagulation in the system. The results showed that sulfates and phosphates formed amorphous complexes with iron species via coprecipitation, thereby promoting coagulation to remove organics. Some heavy metals can also be removed by coagulation. The co-activation of SPC by pre-existing transition metals and the added Fe(Ⅱ) facilitated the oxidative removal of organics, while chloride and arsenic were the main inhibitory inorganic substances in the system. Aromatic compounds mainly promoted coagulation, polysaccharides promoted oxidation, humic acid promoted oxidation and coagulation, and C=C/C=O inhibited the Fe(Ⅱ)/SPC system. The oxidation process removed graphitic structures and unsaturated organic matter in the region of (O/C, H/C) = (0.2–0.4, 0.9–2.0) through free radicals and generated amorphous carbon structures and saturated organic matter in the region of (O/C, H/C) = (0.3–0.7, 1.2–1.9). The coagulation process removed aromatic organics with 2–5 rings and unsaturated organics in the region of (O/C, H/C) = (0.2–0.6, 0.7–1.6) with oxygen-containing organics. The combined effects of coagulation and oxidation enhanced the removal efficiency of organic carbon by approximately 40%. This study facilitates the optimization of hydrothermal carbonization wastewater treatment and advanced oxidation processes.

Changes in plant resource inputs lead to rapid alterations in soil dissolved organic matter composition in an old-growth tropical forest

Alterations in plant resource inputs to soil affect soil organic matter (OM) dynamics. However, it remains unclear how to alter soil dissolved OM (DOM) composition. Here, we used UV/fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry to analyze soil DOM’s optical and molecular characteristics after eight months of detritus input and removal in an old-growth tropical forest. Changes in plant inputs significantly altered soil DOM’s optical properties, and the most pronounced changes were observed in the humification index and fluorescent components. In litterfall removal and no-input plots, molecular characteristic values increased greatly, such as O/C, double-bond equivalent, aromaticity index, and proportion of carboxyl-rich alicyclic molecules, while biolabile compounds decreased. The abundance of lignin-like and tannin-like compounds was more than 20 % higher in litter removal plots than in no-input plots. Our findings indicate that changes in plant resource inputs can lead to rapid alterations in soil DOM composition.

Annotation of DOM metabolomes with an ultrahigh resolution mass spectrometry molecular formula library

Increased accessibility of liquid chromatography mass spectrometry (LC-MS) metabolomics instrumentation and software have expanded their use in studies of dissolved organic matter (DOM) and exometabolites released by microbes. Current strategies to annotate metabolomes generally rely on matching tandem MS/MS spectra to databases of authentic standards. However, spectral matching approaches typically have low annotation rates for DOM. An alternative approach is to annotate molecular formula based on accurate mass and isotopic fine structure measurements that can be obtained from state-of-the-art ultrahigh resolution Fourier Transform Ion Cyclotron Resonance mass spectrometry (FT-ICR MS), but instrument accessibility for large metabolomic studies is generally limited. Here, we describe a strategy to annotate exometabolomes obtained from lower resolution LC-MS systems by matching metabolomic features to a molecular formula library generated for a representative sample analyzed by LC 21T- FT-ICR MS. The molecular formula library approach successfully annotated 53% of exometabolome features of the marine diatom Phaeodactylum tricornutum – a nearly ten-fold increase over the 6% annotation rate achieved using a conventional MS/MS approach. There was 94% agreement between assigned formula that were annotated with both approaches, and mass error analysis of the discrepancies suggested that the FT-ICR MS formula assignments were more reliable. Differences in the exometabolome of P. tricornutum grown under iron replete and iron limited conditions revealed 668 significant metabolites, including a suite of peptide-like molecules released by P. tricornutum in response to iron deficiency. These findings demonstrate the utility of FT-ICR MS formula libraries for extending the accuracy and comprehensiveness of metabolome annotations.

Characterization of sediment organic matter in the outer Yangtze River Estuary using stable isotopes, optical techniques, and FT-ICR-MS: Implications for the carbon burial mechanism

The burial of sediment organic matter (SOM) in the estuary and shelf plays an important role in the global carbon cycle. However, it is challenging to determine the source, composition, and burial of SOM in the coastal sea, especially at the molecular level. This was explored in the coastal area outside the largest Yangtze River of China with multiple techniques including elemental and stable isotopic analysis, absorption spectroscopy, fluorescence excitation-emission matrices coupled with parallel factor analysis (EEMs-PARAFAC), and ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The end-member mixing analysis based on δ13C and δ15N showed a dominance of marine contribution (up to 70%) at most stations while the terrestrial contribution increased to >55% nearshore in summer at a high fluvial sediment flux. This was consistent with the offshore decreasing humic-like C1 and C2, humification index (HIX), %lignin-like compounds, and %CHO but increasing tryptophan-like C3, biological index (BIX), %protein-like compounds, and %CHOS from EEMs-PARAFAC and FT-ICR-MS analysis. The %clay correlated positively with SOM content, HIX, %lignin-like compounds, O/C, and modified aromaticity index (AImod) but correlated negatively with %C3, H/C, and the relative abundance of labile formulas (MLBL), while %silt showed contrasting correlations. These results indicated the fine clay sediments adsorbed more humified, aromatic, oxygenated, and terrestrial compounds that were probably more resistant to biodegradation and thus had a higher burial efficiency than those on the silty sediments. Principal component analysis based on SOM indices further revealed different characteristics of SOM in the nearshore, northern offshore, and southern offshore regions, which were probably dependent on the delivery by local current systems. Overall, these findings contributed to unraveling the source and molecular composition of SOM associated with different grain size sediments and local current delivery, which are fundamental for understanding the factors underlying carbon burial in the complex coastal environment.

Simultaneous Oxidation of Bromide and Dissolution of Manganese Oxide Induced by Freezing.

This study demonstrates that the oxidation of bromide by birnessite (δ-MnO2) results in the concurrent production of soluble manganese (Mn(II)) and reactive bromine (RBr) species in frozen solutions, a process not observed in aqueous solutions. This enhanced oxidation in ice is attributed to the concentration of protons, birnessite, or bromide in the ice grain boundary region. Furthermore, different types of commercial manganese oxides can also oxidize bromide to RBr and release Mn(II) in ice. The presence of fulvic acid (FA) further increases the simultaneous production of RBr and Mn(II) in ice, accompanying the formation of organobromine compounds (OBCs). In frozen δ-MnO2/Br-/FA system, a significant increase in OBCs, mainly highly unsaturated and phenolic compounds, was detected using Fourier transform ion cyclotron resonance mass spectrometry. A marked contrast was observed in the number of OBCs formed in frozen solutions (853 and 415 OBCs at initial pH 3.0 and 5.8, respectively) compared to their aqueous counterparts (11 and 23 OBCs). These findings introduce a new pathway for the formation of RBr, Mn(II), and OBCs in ice, highlighting the need for further research on the environmental fate of bromide and manganese.

Selective Gas-Phase Depletion of Chemical Contaminants in Dissolved Organic Matter Increases Compositional Coverage by FT-ICR Mass Spectrometry.

Fourier transform ion cyclotron resonance mass spectrometry of dissolved organic matter (DOM) extracted from environmental samples provides molecular speciation that enables visualization of compositional trends in the fate and cycling of biogenic and anthropogenic organics. Often, chemical contamination is introduced during field sampling (i.e., remote locations, cannot use glass). Further, preconcentration of DOM by solid-phase extraction often results in chemical contamination. When chemical noise is a dominant fraction of the ion signal, mass spectral performance is degraded by reduction of the ion trap analyte accumulation capacity and enhanced ion cloud dephasing during ICR detection. We have developed gas-phase ion depletion of unwanted chemical contaminants during ion injection into the linear RF ion trap of the hybrid linear ion trap 21 T FT-ICR mass spectrometer that improves detection of analytes by removing unwanted chemical noise. We demonstrate improvements in signal-to-noise ratio, dynamic range, and the number of observed analytes in dissolved organic matter samples that results in a 40-100% increase in the number of identified analytes. In many cases, the number of peaks observed per nominal mass more than doubles over select m/z regions. This gas-phase "clean-up" can salvage precious samples challenged by sampling location, sample volume, or collection protocols that cannot be avoided and maximizes the compositional information obtained. Further, this approach is generalizable and extendable to any hybrid linear ion trap instrument platform (e.g., LTQ-Orbitrap or linear ion trap-TOF). We highlight the power of gas-phase depletion with electrospray ionization, but this method is also applicable to other ionization modes.

Multi-tracer evidence of hydrology and primary production controls on dissolved organic matter composition and stability in the semi-arid aquatic continuum

Autochthonous dissolved organic matter (Auto-DOM) produced by a biological carbon pump using dissolved inorganic carbon (DIC) from carbonate weathering plays an important role in carbon cycling within inland waters. However, little is known regarding how environmental conditions impact the composition and fate of organic matter, especially in surface waters of the semi-arid Loess Plateau, which is enriched in DIC by significant carbonate weathering. To obtain novel insight, we combined hydrochemistry, isotopic composition (δ2H, δ18O, and δ13CDIC), Rayleigh fractionation model, optical spectroscopy (absorbance and fluorescence), and Fourier transform ion cyclotron resonance mass spectrometry measurements to elucidate how primary production and hydrology impact the composition of DOM and the stability of the resulting Auto-DOM throughout the river–reservoir–wetland aquatic continuum of the Bahe River in the carbonate-mineral-rich semi-arid Loess Plateau where carbonate weathering is significant. The Rayleigh fractionation model results indicated that watershed DIC is primarily consumed through aquatic primary production rather than CO2 degassing. Further investigation revealed that primary production and evaporation co-occurred in this watershed. With the enrichment of the stable water isotope δ2H, the relative abundances of the allochthonous compounds decreased and the relative abundances of the autochthonous substances increased, suggesting that the terrestrial signal of riverine DOM decreased while autochthonous production increased along the flow pathway. In addition, associations between optical and molecular characteristics among DOM samples from different water bodies revealed that the stability ratio (Fmax(C2/(C2 + C4))) of Auto-DOM to the ratio of carboxylic-rich alicyclic molecules showed a consistent trend, suggesting that phytoplankton-derived and biomineralized C2 compounds are potentially recalcitrant DOM in inland waters. We conclude that hydrology and primary production affect the source, composition, and, potentially, the stability of DOM in DIC-enriched surface waters of the semi-arid Loess Plateau, which may lead to a more humic-like DOM composition in inland water and export this lower bioavailability DOC to the ocean in the long term.

Molecular–level insights into the synergistic activation of peracetic acid by ultraviolet and ferrous ions for the degradation of sedimentation sludge water in drinking water treatment plants based on Fourier transform-ion cyclotron resonance mass spectrometry

Sedimentation sludge water (SSW) from sedimentation tanks in drinking water treatment plants contains significant amounts of dissolved organic matter (DOM) and precursors of disinfection byproducts, raising increasing concerns about the safety of finished water following SSW recycling. This study explores the alterations in bulk properties and molecular characteristics of DOM in SSW treated with ultraviolet (UV)/ferrous ions (Fe2+) and peracetic acid (PAA) using fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT–ICR MS). The primary reactive species, hydroxyl radicals (·OH) and acylperoxy radicals (CH3C(O)OO·) achieved degradation rates of up to 82.0%, eliminating 84.5% of total fluorescent components and reducing molecular intensity and apparent molecular count by 90.9% and 69.8%, respectively. This treatment significantly reduced the aromaticity of DOM, leading to the formation of more oxidized and stable compounds. Reaction mechanisms indicate that ·OH and CH3C(O)OO· primarily facilitate oxygen addition and dehydrogenation, while CH3C(O)OO· promotes decarboxylation through weak electron transfer processes. The treatment preferentially removes complex DOM containing nitrogen and sulfur heteroatoms, which are key precursors of disinfection byproducts. These findings enhance our understanding of DOM transformations during UV/Fe2+/PAA treatment and provide valuable insights into the safe recycling of SSW.

Targeted and non-targeted identification of dye and chemical contaminants in Loji River, Indonesia using FT-ICR-MS

This study utilized liquid chromatography (LC) alongside Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to explore the dyes and chemical contaminants in Loji River, Indonesia. We tentatively identified a total of 655 contaminants at various confidence level, subsequently classifying them into 22 distinct categories. Of the 54 dyes we detected, 12 corresponded with entries in our specialized in-house database. These 12 dyes were further confirmed by reference standards, matching both retention time (RT) and MS/MS spectra. LC-FT-ICR MS data showed that dyes from printing batik and textile industries are key contributors to river pollution. Particularly noteworthy were two sample locations that displayed substantial contamination, predominantly from azoic and reactive dyes. Additionally, pharmaceuticals were identified as one of the most frequently occurring contaminants, underscoring the inadequacies in the area's sewage management. To corroborate these findings, we conducted physicochemical, phytotoxicity, and acute toxicity tests, all of which verified the harmful effects of the Loji River's water on both the local flora and human populations. Notably, water samples that tested positive for dye contamination exhibited elevated toxicity levels. To the best of our knowledge, this study is pioneering in its molecular-level investigation of dye contamination in Southeast Asian rivers. Our results accentuate the pressing need for both targeted and non-targeted screening methods to identify contaminants in the surface waters of developing nations.

Revisiting Dissolved Organic Matter Analysis Using High-Resolution Trapped Ion Mobility and FT-ICR Mass Spectrometry.

The molecular level characterization of complex mixtures remains an analytical challenge. We have shown that the integration of complementary, high-resolution, gas-phase separations allows for chemical formula level isomeric content description. In the current work, we revisited the current challenges associated with the analysis of dissolved organic matter using high-resolution trapped ion mobility separation (TIMS) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). In particular, we evaluated the separation capabilities provided by TIMS-MS compared to MS alone, the use of ICR complementary data acquisition (DAQ) systems and transient processing strategies, ICR cell geometries (e.g., Infinity cell vs harmonized cell), and magnetic field strengths (7 T vs 9.4 T vs 21 T) for the case of a Harney River DOM sample. Results showed that the external high-performance DAQ enables direct representation of mass spectra in absorption mode FT (aFT), doubling the MS resolution compared to the default magnitude mode FT (mFT). Changes between half- vs full-apodization result in greater MS signal/noise vs superior MS resolving power (RP); in the case of DOM analysis, a 45% increase in assigned formulas is observed when employing the DAQ half (Kaiser-type)-apodization window and aFT when compared to the default instrument mFT. Results showed the advantages of reprocessing 2D-TIMS-FT-ICR MS data with higher RP and magnetic field chemical formulas generated list acquired (e.g., 21 T led to a 24% increase in isomers reported) or the implementation of alternative strategies.

Fast, Easy, and Reproducible Fingerprint Methods for Endotoxin Characterization in Nanocellulose and Alginate-Based Hydrogel Scaffolds.

Nanocellulose- and alginate-based hydrogels have been suggested as potential wound-healing materials, but their utilization is limited by the Food and Drug Administration (FDA) requirements regarding endotoxin levels. Cytotoxicity and the presence of endotoxin were assessed after gel sterilization using an autoclave and UV treatment. A new fingerprinting method was developed to characterize the compounds detected in cellulose nanocrystal (CNC)- and cellulose-nanofiber (CNF)-based hydrogels using both positive- and negative-ion mode electrospray ionization Fourier transform ion cyclotron resonance mass spectroscopy (ESI FT-ICR MS). These biobased hydrogels were used as scaffolds for the cultivation and growth of human dermal fibroblasts to test their biocompatibility. A resazurin-based assay was preferred over all other biocompatibility methodologies since it allowed for the evaluation of viability over time in the same sample without causing cell lysis. The CNF dispersion of 6 EU mL-1 was slightly above the limits, and it did not affect the cell viability, whereas CNC hydrogels induced a reduction of metabolic activity by the fibroblasts. The chemical structure of the detected endotoxins did not contain phosphates, but it encompassed hydrophobic sulfonate groups, requiring the development of new high-pressure sterilization methods for the use of cellulose hydrogels in medicine.

Online Supercritical Fluid Chromatography Hyphenated to Fourier Transform Ion Cyclotron Resonance Mass Spectrometry with Quadrupole Detection for Microalgae Bio-Oil Characterization.

Microalgae are an attractive feedstock for biofuel production thanks to their renewable nature, high growth rate, and ability to use anthropogenic CO2. The conversion of microalgae by hydrothermal liquefaction (HTL) leads to a solid residue, a gaseous phase, and a biocrude. However, the bio-oil is rich in heteroatoms and requires upgrading processes to be used as biofuels. For these treatments to be effective, detailed knowledge of the sample is crucial. The bio-oil was characterized by direct introduction into a Fourier transform ion cyclotron resonance mass spectrometer (DI-FTICR MS) with an electrospray ionization source (ESI). Thousands of molecular formulas were assigned with a high level of confidence, mainly compounds with nitrogen and oxygen atoms. Additionally, the bio-oil was analyzed by coupling supercritical fluid chromatography (SFC) and FTICR to combine the separation power of SFC to the high performances of a 12 T FTICR. Quadrupole detection (2ω) was used in FTICR to have a high resolving power with a lower transient time. The coupling allowed the separation of many isomers along the chromatogram, showing the isomeric complexity of microalgae bio-oils. Moreover, classes of compounds were separated according to their heteroatom class thanks to the SFC separation. In this work, the advantages of DI-FTICR MS and SFC-FTICR MS proved complementary, and DI was useful to study the bio-oil at the molecular scale thanks to the high performances, while SFC proved useful for the characterization at the isomeric scale. This demonstrated the significant potential of this new online hyphenated technique for the characterization of complex matrices.

Synthesis and mechanism of Bi/SnO2 for enhanced photocatalytic activity in the degradation of humic acid under visible light

Humic acid (HA) is a typical refractory organic matter, widely existing in natural water and many types of wastewaters. In this study, Bi/SnO2 composites were synthesized by a simple one-step hydrothermal method for photocatalytic degradation of HA. Due to the surface plasmon resonance (SPR) effect of Bi, the light absorption of Bi/SnO2 composites expands from UV to visible light compared to pure SnO2. Under visible light irradiation for 120 min, the UV254 removal reached 93.58 %, color number (CN) removal reached 94.41 %. The degradation rate constant of Bi/SnO2 (0.0178 min−1) is 14.83 times higher than that of SnO2 (0.0012 min−1), indicating the superior photocatalytic degradation efficiency of Bi/SnO2 composites. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was found that photocatalysis mainly degraded most CHO-containing organic matter and reduced the amount of organic matter (from 7240 to 3886). The molecular number of organic compounds with m/z of 400–500 and 500–600 exhibited a significant decrease, specifically by 1052 and 770, respectively. This observation suggests that the photocatalytic process effectively eliminates low and moderate molecular weight organics. The molecular number, aromaticity and molecular weight of dissolved organic matter (DOM) were reduced mainly by carboxylic acid reaction, dealkylation reaction and oxygen addition reaction.

Simultaneously reducing methane emissions and arsenic mobility by birnessite in flooded paddy soil: Overlooked key role of organic polymerisation

Flooding of paddy fields enhances methane (CH4) emissions and arsenic (As) mobilisation, which are crucial issues for agricultural greenhouse gas emissions and food safety. Birnessite (δ-MnO2) is a common natural oxidant and scavenger for heavy metals. In this study, birnessite was applied to As-contaminated paddy soil. The capacity for simultaneously alleviating CH4 emissions and As mobility was explored. Soil microcosm incubation results indicated that birnessite addition simultaneously reduced CH4 emissions by 47 %–54 % and As release by 38 %–85 %. The addition of birnessite decreased the dissolved organic carbon (DOC) contents and altered its chemical properties. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) results showed that birnessite reduced the labile fractions of proteins, carbohydrates, lignins, tannins, and unsaturated hydrocarbons, however, increased the abundance of condensed aromatic structures, suggesting the polymerisation of dissolved organic matter (DOM) by birnessite. The degradation of labile fractions and the polymerisation of DOM resulted in an inventory of recalcitrant DOM, which is difficult for microbes to metabolise, thus inhibiting methanogenesis. In contrast, birnessite addition increased CH4 oxidation, as the particulate methane monooxygenase (pmoA) gene abundance increased by 30 %. The enhanced polymerisation of DOM by birnessite also increased As complexation with organics, leading to the transfer of As to the organic bound phase. In addition, the decrease in ferrous ion [Fe(II)] concentrations with birnessite indicated that the reductive dissolution of Fe oxides was suppressed, which limited the release of arsenite [As(III)] under reducing conditions. Furthermore, birnessite decreased As methylation and shaped the soil microbial community structure by enriching the metal-reducing bacterium Bacillus. Overall, our results provide a promising method to suppress greenhouse gas emissions and the risk of As contamination in paddy soils, although further studies are needed to verify its efficacy and effectiveness under field conditions.

Molecular-level insight into the effect of fertilization regimes on the chemodiversity of dissolved organic matter in tropical cropland

Fertilization is a critical agronomic measure for croplands in tropical regions, owing to their low fertility. However, the effects of fertilization on the quantity and chemodiversity of latosolic dissolved organic matter (DOM) in tropical regions remain largely unknown. Therefore, in this study, the variations in latosol DOM concentrations and chemodiversity induced by inorganic fertilization and the co-application of inorganic fertilization with straw return, sheep manure, biochar, and vermicompost fertilizers at a molecular level were systematically investigated using multispectral techniques and ultrahigh-resolution mass spectrometry. In line with our expectations, the results showed that combined inorganic-organic fertilization improved soil quality by increasing soil organic carbon content compared to that under inorganic fertilization. However, as the most active and bioavailable organic carbon pool, dissolved organic carbonconcentrations between the fertilization treatments were not significantly different (p = 0.07). However, the dissolved organic carbon concentrations under combined inorganic-organic fertilization treatment (NPK plus straw return, 263.45 ± 37.51 mg/kg) were lower than those under inorganic fertilization treatment (282.10 ± 18.57 mg/kg). Spectral analysis showed that the DOM in the combined inorganic-organic fertilization treatments had a higher degree of humification and lower autogenetic contributions. Furthermore, Fourier transform ion cyclotron resonance mass spectrometry analysis indicated that the combined inorganic-organic fertilization increased the chemodiversity of latosolic DOM and promoted the production of large, oxidized, and stable molecules, including lignin, aromatic, and tannin compounds, which potentially benefits soil carbon sequestration in tropical regions. This study could provide a theoretical basis for elucidating on the potentially relevant ecological functions and environmental effects of DOM under fertilization regimes.