Thermochemolysis Gas Research Articles

Early decomposition and transformation of organic matter in natural and disturbed boreal forests

The state of boreal larch forests near the southern permafrost margin in eastern Eurasia varies considerably, even on a local scale, as a result of anthropogenic disturbances (e.g., clear-cuts and fires) and uneven permafrost distribution. This study aimed to investigate whether various ecosystem conditions affect litter decomposition and organic matter (OM) transformation. Here, we present the results of a field experiment in natural and disturbed larch stands utilising the Tea-Bag Index approach (TBI). We investigated the decomposition in four larch stands in different states (post-fire, clear-cut, permafrost and control). Besides standard TBI indexes, we studied the transformation of OM composition by thermochemolysis–gas chromatography mass spectrometry. Mass loss differed depending on litter quality rather than forest disturbance type or permafrost. No significant differences were found between stabilisation (S) and decomposition constant (k) in disturbed and unaffected forests, whereas soil properties were differently related to decomposition parameters at the study sites. Our results on molecular composition before and after the incubation suggest site-depending, mainly microbial transformation of green tea in various forest conditions. Rooibos did not undergo a considerable microbial transformation. We showed that S and k might not be sensitive to various ecosystem conditions (e.g., disturbances and permafrost). However, the transformation of OM may vary, even on a local scale, having significant implications for carbon sequestration in soil. Our study shows that not a mass loss but a transformation of OM might depend on various conditions of the larch ecosystem at the southern margin of permafrost distribution in eastern Eurasia.

Characterization of Lignin Biodegradation in Ashwood by Ganoderma Spp. Using Ligninolytic Enzymes and Tmah Thermochemolysis–Gas Chromatography–Mass Spectrometry

Characterization of Lignin Biodegradation in Ashwood by Ganoderma Spp. Using Ligninolytic Enzymes and Tmah Thermochemolysis–Gas Chromatography–Mass Spectrometry

Plant versus microbial signature in densimetric fractions of Mediterranean forest soils: a study by thermochemolysis gas chromatography mass spectrometry

Soil organic matter (SOM) ageing may be measured by means of molecular signatures, ratios between organic compounds which inform us about the origin and/or the degree of biochemical evolution of (or microbial contribution to) specific groups of compounds: lipids, proteins, carbohydrates, etc. Owing to the biochemical heterogeneity of decomposing substrates, it is unlikely that the degree of biochemical evolution can be approached with a single ratio. Nevertheless, obtaining a wide collection of molecular signatures can be costly. Instead of applying specific methods to obtain a collection of ratios, we apply thermally assisted hydrolysis and methylation (THM), followed by GC-MS, to obtain a panoramic view of SOM composition. From the compounds identified after THM, several ratios were obtained. Three ratios are based on aliphatic compounds: (1) ratio between short-chain (≤ 20 C) and long-chain (> 20 C) alkanoic acids, (2) ratio between branched and long-chain alkanoic acids, (3) ratio between short-chain (C18) and long-chain (C22–C24) alkanols. Four ratios are based on lignin-derived monomers: (4) vanillic acid to vanillin, (5) syringic acid to syringaldehyde, (6) a combination of the two previous, and (7) the syringyl- to total lignin monomers. Finally, three ratios are based on sugar composition: (8) fucose to glucose, (9) xylose to glucose, and (10) fucose to xylose. These ratios were applied to the study of several densimetric fractions from three organic OH horizons from Mediterranean forest soils. The fractionation gave a free-light fraction (LF), of density 2.0. The three lightest fractions (LF, OC1, and OC2) seem the least microbially reworked, whereas the denser fractions, OC3 and DF, seem the most evolved ones. Nevertheless, this is valid only as an average result, for no single fraction is made of fresh compounds only, or of highly evolved compounds only, either. The behaviour of the several ratios was inconsistent because some behave in ways opposite to the expected ones. All fractions show signs of both advanced biochemical evolution and preservation of fresh, plant-derived labile compounds. This, added to the inconsistent behaviour of many signatures, suggests that our views about the biochemical evolution of plant debris during their decomposition and humification are probably too simple.

Molecular characterization of primary humic-like substances in fine smoke particles by thermochemolysis–gas chromatography–mass spectrometry

In this study, the molecular structures of primary humic-like substances (HULIS) in fine smoke particles emitted from the combustion of biomass materials (including rice straw, corn straw, and pine branches) and coal, and atmospheric HULIS were determined by off-line tetramethylammonium hydroxide thermochemolysis coupled with gas chromatography and mass spectrometry (TMAH-GC/MS). A total of 89 pyrolysates were identified by the thermochemolysis of primary and atmospheric HULIS. The main groups were polysaccharide derivatives, N-containing compounds, lignin derivatives, aromatic acid methyl ester, aliphatic acid methyl ester, and diterpenoid derivatives. Both the type and distribution of pyrolysates among primary HULIS were comparable to those in atmospheric HULIS. This indicates that primary HULIS from combustion processes are important contributors to atmospheric HULIS. Some distinct differences were also observed. The aromatic compounds, including lignin derivatives and aromatic acid methyl ester, were the major pyrolysates (53.0%–84.9%) in all HULIS fractions, suggesting that primary HULIS significantly contributed aromatic structures to atmospheric HULIS. In addition, primary HULIS from biomass burning (BB) contained a relatively high abundance of lignin and polysaccharide derivatives, which is consistent with the large amounts of lignin and cellulose structures contained in biomass materials. Aliphatic acid methyl ester and benzyl methyl ether were prominent pyrolysates in atmospheric HULIS. Moreover, some molecular markers of specific sources were obtained from the thermochemolysis of primary and atmospheric HULIS. For example, polysaccharide derivatives, pyridine and pyrrole derivatives, and lignin derivatives can be used as tracers of fresh HULIS emitted from BB. Diterpenoid derivatives are important markers of HULIS from pine wood combustion sources. Finally, the differences in pyrolysate types and the distributions between primary and atmospheric HULIS suggested that the primary HULIS would undergo many atmospheric processes to reconstruct the macromolecular organic matter in atmospheric aerosols.

Modern sediment records of stanol to sterol ratios in Lake Suigetsu, Japan: An indicator of variable lacustrine redox conditions

We tested the usefulness of the 5α(H)-stanol/Δ5-sterol ratios obtained by the tetramethylammonium hydroxide (TMAH) thermochemolysis gas chromatography–mass spectrometry (GC–MS) method used to reconstruct redox events in marine sediments as a redox tracer in lake sediments using cores from Lake Suigetsu, Japan. The lake was previously a freshwater lake and is now brackish owing to excavation works conducted during the 17th century. Other redox tracer analyses (e.g., based on farnesol) have shown that C26(nor-24)Δ22/C26(nor-24)Δ5,22 (24-nordehydrocholestanol/24-nordehydrocholesterol), C28(24Me)Δ22/C28(24Me)Δ5,22 (diatomstanol/diatomsterol), and C27Δ22/C27Δ5,22 (22-dehydrocholestanol/22-dehydrocholesterol) ratios have risen (∼0.53) following strong anoxic conditions that formed in Lake Suigetsu (A.D. 1848 and 1935). This study is the first to show that 5α(H)-stanol/Δ5-sterol ratios determined using the TMAH method could be useful as a redox tracer in lacustrine environments. In particular, the ratio of diatomsterol, which is detected in both brackish and fresh water in relatively high abundance, has the potential to be a very useful tracer of redox events. On the other hand, the other 5α(H)-stanol/Δ5-sterol ratios (C27Δ0/C27Δ5 [cholestanol/cholesterol], C28(24Me)Δ0/C28(24Me)Δ5 [campestanol/campesterol], and C29(24Et)Δ0/C29(24Et)Δ5 [sitostanol/sitosterol] ratios) showed no increasing trends, suggesting the influence of terrestrial inputs from degraded products.

Rapid determination of ginkgolic acids in Ginkgo biloba kernels and leaves by direct analysis in real time-mass spectrometry.

A novel method based on direct analysis in real time integrated with mass spectrometry was established and applied into rapid determination of ginkgolic acids in Ginkgo biloba kernels and leaves. Instrument parameter settings were optimized to obtain the sensitive and accurate determination of ginkgolic acids. At the sample introduction speed of 0.2mm/s, high intensity of [M-H]- ions for ginkgolic acids were observed in the negative ion mode by utilization of high-purity helium gas at 450°C. Two microliters of methanol extract of G. biloba kernels or leaves dropped on the surface of Quick-Strip module was analyzed after solvent evaporated to dryness. A series of standard solutions of ginkgolic acid 13:0 in the range of 2-50mg/L were analyzed with a correlation coefficient r=0.9981 and relative standard deviation (n=5) from 12.5 to 13.7%. The limit of detection was 0.5mg/L. The results of direct analysis in real time-mass spectrometry were in agreement with those observed by thermochemolysis gas chromatography. The proposed method demonstrated significant potential in the application of the high-throughput screening and rapid analysis for ginkgolic acids in dietary supplements.

Stanol to sterol ratios in late Quaternary sediments from southern California: An indicator for continuous variability of the oxygen minimum zone

In this study, we analyzed 5α(H)-stanol/Δ5-sterol ratios in offshore marine sediments using offline tetramethylammonium hydroxide thermochemolysis (TMAH) gas chromatography–mass spectrometry (GC–MS). Data were used to reconstruct redox events recorded in a southern California marine sediment core (Ocean Drilling Program, Leg167, Hole 1017E). The 24-nordehydrocholestanol/24-nordehydrocholesterol and diatomstanol/diatomsterol ratios clearly recorded oxygen minimum zone (OMZ) fluctuations in southern California during the last 40kyr. In particular, two ratios corresponding to Marine Isotope Stage 3 (MIS3) varied significantly at the OMZ, exhibiting millennial-scale fluctuations related to Dansgaard-Oeschger shifts of warming and cooling intervals. In contrast, other ratios (cholestanol/cholesterol, campestanol/campesterol, sitostanol/sitosterol, and 22-dehydrocholestanol/22-dehydrocholesterol) showed no significant trends, possibly reflecting the influence of stanol-creating organisms. Our results show that 5α(H)-stanol/Δ5-sterol ratios obtained using the TMAH GC–MS method are useable tracers of water column and surface sediment redox conditions in southern California marine sediments.

Decomposition of bio-degradable plastic polymer in a real on-farm composting process

The current wide diffusion of bio-degradable plastic made up by starch-based polymeric composite has focused the attention on the allocation of bio-polymers for the direct recycling in composting processes. Actually, the acknowledged current methods to estimate the bio-degradability are mainly based on laboratory tests and measurements under controlled conditions, while scarce information are available on the effective transformation of bio-film derivatives in real composting facilities. The aim of this paper was to determine at molecular level the decomposition of specific starch-based thermoplastic mulching film for horticultural crops, in a real on-farm composting system for the attainment of mature compost for agricultural application. The initial and final molecular composition of both bulk biomasses and bio-plastic composite were evaluated through 13C solid-state CPMAS-NMR spectroscopy and off-line thermochemolysis—gas chromatography–mass spectrometry. The effective decomposition of the bio-polymer was shown by mono-dimensional and pseudo-2D NMR experiments that revealed the alteration of the intermolecular linkages among the monomeric constituents, while the thermochemolysis confirmed the complete decomposition of starch components. Concomitantly, the molecular characterization of bulk compost indicated the typical selective preservation of hydrophobic components currently found in aerobic composting processes, with a significant increase (+50 %) for the yields of aromatic lignin derivatives and recalcitrant aliphatic compounds. In addition to the classical testing methodologies, the detailed analytical investigation represents a powerful methodology to elucidate the molecular composition and modification of plastic bio-polymers thereby providing a valuable contribution to further promote the composting process as viable way to recycle the biodegradable polymeric materials.

Chemical Characterization and Botanical Origin of French Ambers.

The molecular composition of 10 Cretaceous and one Eocene ambers from France was analyzed by infrared spectroscopy, solid-state (13)C nuclear magnetic resonance spectroscopy, and thermochemolysis gas chromatography-mass spectrometry. The terpenoids identified in the samples were used as biomarkers for the botanical origin of the resins. The Cretaceous samples, comprising the so-called Alpine, Anjou, Charentese, Provence, Pyrenean, and Vendean ambers, ranged from the Albian-Cenomanian transition to the early Santonian (100 to 85 Ma) and correspond to class Ib resins typical of conifers. The extinct conifer family Cheirolepidiaceae was proposed as the plant source of Pyrenean and brown Charentese ambers. Araucariaceae or Cheirolepidiaceae were the plant sources of the Cenomanian Alpine, Anjou, and yellow Charentese ambers. The Santonian ambers of Provence and Vendée were found to derive from the Cupressaceae. The Eocene Oise amber (ca. 53 Ma) is a class Ic resin typical of angiosperms and was produced by a Fabaceae. The evolution of resin sources from the early Cretaceous to the Eocene periods is discussed. Finally, a possible fingerprint hitherto unveiled is proposed for cheirolepidiaceous resins, defined by the simultaneous presence of phenolic diterpenoids, labdanoic acids, callitrisate structures, and their respective derivatives.

Molecular composition and chemotaxonomic aspects of Eocene amber from the Ameki Formation, Nigeria

The molecular composition of fossil resin from the Eocene Ameki Formation, southern Nigeria has been analyzed by infrared spectroscopy, pyrolysis–gas chromatography–mass spectrometry and thermochemolysis gas chromatography–mass spectrometry to determine the structural class and botanical source of the resin. The pyrolysis products were dominated by bicyclic products derived from regular labdatriene structure and lacked succinic acid indicating Class Ib type amber. The biomarker compositions in the pyrolysates are dominated by sesquiterpenoids of the cadinane and bisabolane classes that are common constituents of higher plants and labdane type diterpenoids. The exclusive presence of labdane type diterpenoids and the absence of higher plant triterpenoids strongly suggest that the amber was derived from a gymnosperm (conifer) botanical source. This observation contrasts with the angiosperm source previously suggested for the resin based on the palaeobotanical studies of the host sediments. The specific family source within the conifers could not be ascertained based on the molecular composition of the resin. However, the presence of methyl-16,17-dinor-callitrisate pointed to the Cupressaceae family although other Cupressaceae biomarker indicators were not detected in the resin.

Molecular properties of a fermented manure preparation used as field spray in biodynamic agriculture

Manure products fermented underground in cow horns and commonly used as field spray (preparation 500) in the biodynamic farming system, were characterized for molecular composition by solid-state nuclear magnetic resonance [(13) C cross-polarization magic-angle-spinning NMR ((13) C-CPMAS-NMR)] spectroscopy and offline tetramethylammonium hydroxide thermochemolysis gas chromatography-mass spectrometry. Both thermochemolysis and NMR spectroscopy revealed a complex molecular structure, with lignin aromatic derivatives, polysaccharides, and alkyl compounds as the predominant components. CPMAS-NMR spectra of biodynamic preparations showed a carbon distribution with an overall low hydrophobic character and significant contribution of lignocellulosic derivatives. The results of thermochemolysis confirmed the characteristic highlighted by NMR spectroscopy, revealing a molecular composition based on alkyl components of plant and microbial origin and the stable incorporation of lignin derivatives. The presence of biolabile components and of undecomposed lignin compounds in the preparation 500 should be accounted to its particularly slow maturation process, as compared to common composting procedures. Our results provide, for the first time, a scientific characterization of an essential product in biodynamic agriculture, and show that biodynamic products appear to be enriched of biolabile components and, therefore, potentially conducive to plant growth stimulation.

Characterization of Alkylphenol Components in Ginkgo biloba Sarcotesta by Thermochemolysis–Gas Chromatography/Mass Spectrometry in the Presence of Trimethylsulfonium Hydroxide

A method to determine alkylphenols in Ginkgo biloba sarcotesta, especially focusing on polyunsaturated ginkgolic acid components, was developed on the basis of thermochemolysis–gas chromatography/mass spectrometry with a DB-23 column in the presence of trimethylsulfonium hydroxide [(CH3)3SOH]. By using this technique, powder sample of Ginkgo biloba sarcotesta can be directly analyzed without any tedious and time-consuming pretreatment. On the resulting chromatograms, seven kinds of ginkgolic acids including polyunsaturated ginkgolic acid GA17:2 and two kinds of ginkgols were clearly observed as their methyl derivative. Based on the peak areas, the ginkgolic acid compositions are in good agreement with these obtained by a high-performance liquid chromatography method dedicated to analysis of ginkgolic acid.

Direct analysis of fatty acid profile from milk by thermochemolysis–gas chromatography–mass spectrometry

The fatty acid composition of milk is of considerable interest due to their nutritional and functional properties. Although rapid milk fat separation and transesterification procedures have been developed, the overall procedure remains time consuming, specially, for the analysis of a large number of samples. In this work, a fast and simple method for direct profiling of fatty acids from milk using thermochemolysis has been developed. This method has the capability of directly analyse fatty acids from one drop of milk without fat extraction or cleanup. Our approach for thermochemolysis is based on thermal desorption integrated with a cold trap inlet. The optimized method does not present isomerisation/degradation of polyunsaturated fatty acid and shows milk fatty acid profiles comparable to the conventional method based on fat extraction and alkaline transesterification. Overall, this method has demonstrated significant potential for high throughput analysis of fatty acids in milk.

Terpenoid composition and botanical affinity of Cretaceous resins from India and Myanmar

Fossil resins from the Cretaceous sediments of Meghalaya, India and Kachin, Myanmar (Burma) were analysed using Curie point pyrolysis–gas chromatography–mass spectrometry and thermochemolysis gas chromatography–mass spectrometry to help elucidate their botanical source. The major pyrolysis products and methyl-esterified thermochemolysis products of both the resins were abietane and labdane type diterpenoids with minor amount of sesquiterpenoids. The thermochemolysis products also included methyl-16,17-dinor callitrisate, methyl-16,17-dinor dehydroabietate and methyl-8-pimaren-18-oate—the latter two from just the Myanmarese resin. The exclusive presence of both labdane and abietane diterpenoids and the lack of phenolic terpenoids may suggest that the studied Cretaceous resins were derived from Pinaceae (pine family) conifers. ► The chemical composition of Cretaceous resins from India and Myanmar was investigated. ► Abietane and labdane type diterpenoids are the major pyrolysis products. ► These resins were probably derived from Pinaceae conifers.

Recent applications in analytical thermochemolysis

This review outlines and discusses the recent development of thermochemolysis (or thermally assisted hydrolysis and methylation (THM)) since the review paper by Challinor in this journal in 2001. The concept and practice of thermochemolysis using quaternary ammonium base reagents, e.g., tetramethylammonium hydroxide (TMAH), is given. The application review is categorized based on either the class of compounds, or popular sample types, e.g., soils, pollen etc. using thermochemolysis gas chromatography–mass spectrometry (GC–MS). Quantitative analysis, a relatively new aspect of thermochemolysis, is discussed separately, where appropriate, at the end of some of application sections. The wide variety of applications includes synthetic polymers, lipids, materials in art and conservation, lignin, carbohydrates, amino acids, proteins and nucleic acids, flavonoids, soil/sediments, atmosphere particulates, human samples, and others. A section is devoted to chemometric techniques and data analysis of thermochemolysis products.

Rapid and direct characterization of total fatty acids in wood by thermochemolysis–gas chromatography–flame ionization detector/mass spectrometry with tetrabutylammonium hydroxide

Conventional methods used to analyze total fatty acids in wood generally require tedious and time-consuming pretreatments such as solvent extraction and hydrolysis of esterified fatty acids of fats. In this study, both total fatty acid composition and the yield from free and esterified fatty acids of fats in Acacia species were investigated using a rapid and direct method of thermochemolysis–gas chromatography (GC)–flame ionization detector (FID)/mass spectrometry (MS) with organic alkalis. Using tetrabutylammonium hydroxide (TBAH) at 300 °C, thermochemolysis–GC–FID/MS gave total fatty acids including the fat origin as pyrolyzates with suppressed lignin fragment formation because of the basicity of TBAH compared to other organic alkalis: tetramethylammonium hydroxide and tetramethylammonium acetate. The obtained results of fatty acid composition were consistent with those obtained using conventional methods consisting of a series of procedures such as solvent extraction, hydrolysis, derivatization, and analysis by GC–FID/MS in fatty acid composition analysis. Furthermore, thermochemolysis–GC–FID gave a higher yield of total fatty acid than the conventional method, quantitatively reflecting the difficulty in solvent extraction of these components. Consequently, thermochemolysis–GC with TBAH promises to be a rapid and direct method to characterize total fatty acids in wood, avoiding artifacts by solvent extraction of wood. Furthermore, this method discriminated Acacia auriculiformis from Acacia mangium based on the observed fatty acid contents and selected individuals containing low total fatty acids to minimize paper sliding on a printer drum.

Use of an injection port for thermochemolysis–gas chromatography/mass spectrometry: Rapid profiling of biomaterials

A simple and direct approach was developed for thermochemolytic analysis of a wide range of biomolecules present in plant materials using an injection port of a gas chromatograph/mass spectrometer (GC/MS) and a novel solids injector consisting of a coiled stainless steel wire placed inside a modified needle syringe. Optimum thermochemolysis (or Thermally Assisted Hydrolysis/Methylation) was achieved by using a suitable methanolic solution of trimethylsulfonium hydroxide (TMSH) or tetramethylammonium hydroxide (TMAH) with an injection port temperature of 350 °C. Intact, methylated flavonoids, saccharides, phenolic and fatty acids, lignin dimers and diterpene resin acids were identified. Samples include tea leaves, hemicelluloses, lignin isolates and herbal medicines. Unexpected chromatographic results using TMAH reagent revealed the presence of intact methylated trisaccharides (658 Da) and structurally informative dimer lignin markers.

Direct analysis of alkylphenols in Ginkgo biloba leaves by thermochemolysis–gas chromatography/mass spectrometry in the presence of tetramethylammonium hydroxide

Thermochemolysis–gas chromatography/mass spectrometry (GC/MS) in the presence of tetramethylammonium hydroxide (TMAH) was applied to the determination of alkylphenols in Ginkgo biloba leaves directly using a vertical microfurnace pyrolyzer. TMAH thermochemolysis–GC enabled the highly sensitive determination of alkylphenols including ginkgolic acids and ginkgols in G. biloba leaves as their methyl derivatives on the resulted pyrograms. On the basis of their peak areas, the contents of the alkylphenols in G. biloba leaf sample were rapidly and precisely determined without using any tedious and time-consuming pretreatment.

Rapid determination of spore chemistry using thermochemolysis gas chromatography-mass spectrometry and micro-Fourier transform infrared spectroscopy

Spore chemistry is at the centre of investigations aimed at producing a proxy record of harmful ultraviolet radiation (UV-B) through time. A biochemical proxy is essential owing to an absence of long-term (century or more) instrumental records. Spore cell material contains UV-B absorbing compounds that appear to be synthesised in variable amounts dependent on the ambient UV-B flux. To facilitate these investigations we have developed a rapid method for detecting variations in spore chemistry using combined thermochemolysis gas chromatography-mass spectrometry and micro-Fourier transform infrared spectroscopy. Our method was tested using spores obtained from five populations of the tropical lycopsid Lycopodium cernuum growing across an altitudinal gradient (650-1981 m a.s.l.) in S.E. Asia with the assumption that they experienced a range of UV-B radiation doses. Thermochemolysis and subsequent pyrolysis liberated UV-B pigments (ferulic and para-coumaric acid) from the spores. All of the aromatic compounds liberated from spores by thermochemolysis and pyrolysis were active in UV-B protection. The various functional groups associated with UV-B protecting pigments were rapidly detected by micro-FTIR and included the aromatic C[double bond, length as m-dash]C absorption band which was exclusive to the pigments. We show increases in micro-FTIR aromatic absorption (1510 cm(-1)) with altitude that may reflect a chemical response to higher UV-B flux. Our results indicate that rapid chemical analyses of historical spore samples could provide a record ideally suited to investigations of a proxy for stratospheric O3 layer variability and UV-B flux over historical (century to millennia) timescales.

Probing the oxidation–reduction properties of terrestrially and microbially derived dissolved organic matter

Dissolved organic matter (DOM) has been shown to be an integral component in biogeochemical electron transfer reactions due to its demonstrated ability to facilitate redox reactions. While the role of DOM as a facilitator of electron transfer processes has been demonstrated, greater knowledge would lead to better understanding of the structural components responsible for redox behavior, such as quinones and nitrogen and sulfur (N/S) functional groups. This investigation uses direct scan voltammetry (DSV) coupled with fluorescence and NMR spectroscopy as well as thermochemolysis gas chromatography mass spectrometry (GC–MS) and X-ray photoelectron spectroscopy (XPS) to elucidate the organic moieties responsible for facilitating electron transfer reactions. We contrast electrochemical properties and structural details of three organic matter isolates from diverse sources; Great Dismal Swamp DOM (terrestrially derived, highly aromatic), Pony Lake DOM (microbially derived, highly aliphatic) and Toolik Lake (terrestrially derived, photochemically and microbially altered) with juglone (a redox-active model quinone). Aromatic and phenolic constituents were detected (by 13C NMR) and recovered (by thermochemolysis GC–MS) from all three fulvic acid samples, highlighting the ubiquity of these compounds and suggesting that the quinone–phenol redox couple is not limited to DOM derived from lignin precursors. The range of hydroxy-benzene and benzoic acid derivatives may explain the lack of a single pair of well-defined oxidation and reduction peaks in the DSV scans. The presence of a wide-range of hydroxylated benzoic acid isomers and other redox-active aromatic residues implies that native DOM possesses overlapping redox potentials analogous to their characteristic range of p K a values.