Revealing the backbone structures of land-based fulvic acids derived from river and soil through n-butylsilane reduction.

While ultra-high-resolution mass spectrometry has enabled the identification of the molecular composition of dissolved organic matter (DOM), elucidating its molecular structure remains a challenging endeavor. Here, two fulvic acids (FAs), one from river and the other from forest soil, were subjected to reduction using an optimized n-butylsilane (n-BS) reduction method. The reduction products were purified through a combination of liquid-liquid extraction and silica gel column chromatography, resulting in the separation into saturates, aromatics, and polar products.

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.

Niche differentiation of microbial community shapes vertical distribution of recalcitrant dissolved organic matter in deep-sea sediments.

Sedimentary organic matter provides carbon substrates and energy sources for microorganisms, which drive benthic biogeochemical processes and in turn modify the quantity and quality of dissolved organic matter (DOM). However, the molecular composition and distribution of DOM and its interactions with microbes in deep-sea sediments remain poorly understood. Here, molecular composition of DOM and its relationship with microbes were analyzed in samples collected from two sediment cores (∼40 cm below the sea floor), at depths of 1157 and 2253 m from the South China Sea.

Direct Production of Bio-Recalcitrant Carboxyl-Rich Alicyclic Molecules Evidenced in a Bacterium-Induced Steroid Degradation Experiment.

Carboxyl-rich alicyclic molecules (CRAM) are highly unsaturated compounds extensively distributed throughout aquatic environments and sediments. This molecular group is widely referred to as a major proxy of recalcitrant organic materials, but its direct biosynthesis remains unclear. Steroids are a typical anthropogenic contaminant and have been previously suggested to be precursors of CRAM; however, experimental evidence to support this hypothesis is lacking.

Experimental Insight into the Enigmatic Persistence of Marine Refractory Dissolved Organic Matter.

More than 90% of marine dissolved organic matter (DOM) is biologically recalcitrant. This recalcitrance has been attributed to intrinsically refractory molecules or to low concentrations of molecules, but their relative contributions are a long-standing debate. Characterizing the molecular composition of marine DOM and its bioavailability is critical for understanding this uncertainty.

Investigation of the molecular structure complexity of dissolved organic matter by UPLC-orbitrap MS/MS.

The complex natural organic matter of the Suwannee River fulvic acid (SRFA) standard was analyzed by online reversed-phase chromatography with Orbitrap MS/MS using collision-induced dissociation (CID). The number of isobars per nominal mass could be reduced to a single dominantly abundant species in a chromatographic run, sharing some ions with signals having the identical molecular formula in adjacent chromatographic segments and later serving as a precursor ion for fragmentation. A very large proportion of the same fragment ions existed in adjacent chromatographic fractions.

Microbial transformation of distinct exogenous substrates into analogous composition of recalcitrant dissolved organic matter.

Oceanic dissolved organic matter (DOM) comprises a complex molecular mixture which is typically refractory and homogenous in the deep layers of the ocean. Though the refractory nature of deep-sea DOM is increasingly attributed to microbial metabolism, it remains unexplored whether ubiquitous microbial metabolism of distinct carbon substrates could lead to similar molecular composition of refractory DOM. Here, we conducted microbial incubation experiments using four typically bioavailable substrates (L-alanine, trehalose, sediment DOM extract, and diatom lysate) to investigate how exogenous substrates are transformed by a natural microbial assemblage.

Molecular-level transformation characteristics of refractory organics in landfill leachate during ozonation treatment.

Macromolecular refractory organics in landfill leachate are extremely complex compounds. This study examined the molecular-level transformation characteristics of refractory organics in biologically-treated landfill leachate (i.e.

In-House Standard Method for Molecular Characterization of Dissolved Organic Matter by FT-ICR Mass Spectrometry.

Electrospray ionization (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been widely used for molecular characterization of dissolved organic matter (DOM). However, ESI FT-ICR MS generally has poor repeatability and reproducibility because of its inherent ionization mechanism and structural characteristics, which severely hindered its application in quantitative analysis of complex mixtures. In this article, we developed an in-house standard method for molecular characterization of DOM by ESI FT-ICR MS.

Molecular investigation into the transformation of dissolved organic matter in mature landfill leachate during treatment in a combined membrane bioreactor-reverse osmosis process.

This study investigated the effectiveness of a combined membrane bioreactor (MBR) and reverse osmosis (RO) process for treating leachate produced by a large-scale anaerobic landfill. The MBR process had limited treatment efficiency for removing organic pollutants, but when combined with RO, the integrated system completely removed macromolecular compounds (i.e.

Validation and Evaluation of High-Resolution Orbitrap Mass Spectrometry on Molecular Characterization of Dissolved Organic Matter.

Molecular composition of dissolved organic matter (DOM) is a hot topic in subjects such as environmental science and geochemistry. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been applied to molecular composition characterization of DOM successfully. However, high instrument and maintenance costs have constrained its wider application.