CuO Oxidation Research Articles

Quantification of lignin oxidation products as vegetation biomarkers in speleothems and cave drip water

Abstract. Here we present a sensitive method to analyze lignin oxidation products (LOPs) in speleothems and cave drip water to provide a new tool for paleo-vegetation reconstruction. Speleothems are valuable climate archives. However, compared to other terrestrial climate archives, such as lake sediments, speleothems contain very little organic matter. Therefore, very few studies on organic biomarkers in speleothems are available. Our new sensitive method allows us to use LOPs as vegetation biomarkers in speleothems. Our method consists of acid digestion of the speleothem sample followed by solid-phase extraction (SPE) of the organic matter. The extracted polymeric lignin is degraded in a microwave-assisted alkaline CuO oxidation step to yield monomeric LOPs. The LOPs are extracted via SPE and finally analyzed via ultrahigh-performance liquid chromatography (UHPLC) coupled to electrospray ionization (ESI) and high-resolution Orbitrap mass spectrometry (HRMS). The method was applied to stalagmite samples with a sample size of 3–5 g and cave drip water samples with a sample size of 100–200 mL from the Herbstlabyrinth-Advent Cave in Germany. In addition, fresh plant samples, soil water, and powdered lignin samples were analyzed for comparison. The concentration of the sum of eight LOPs (Σ8) was in the range of 20–84 ng g−1 for the stalagmite samples and 230–440 ng L−1 for the cave drip water samples. The limits of quantification for the individual LOPs ranged from 0.3–8.2 ng per sample or 1.5–41.0 ng mL−1 of the final sample solution. Our method represents a new and powerful analytical tool for paleo-vegetation studies and has great potential to identify the pathways of lignin incorporation into speleothems.

Ultralow Sample Volume Cupric Sulfate Oxidation Method for the Analysis of Dissolved Lignin.

A novel cupric sulfate (CuSO4) oxidation method was developed to enable the analysis of dissolved lignin phenols in small volumes of open ocean seawater (<200 mL for deep ocean) or river water (<17 mL) samples. Dissolved lignin phenols were isolated by automated reversed-phase (octadecyl) extraction from seawater before oxidation, whereas for freshwater samples, oxidation was performed without prior extraction. Optimized reaction conditions using alkaline CuSO4 at 150 °C effectively limited losses of lignin phenols and suppressed side reactions at 5-100 μg of sample organic carbon. The method yielded up to ∼33% higher lignin phenol concentrations and 24-36% lower acid/aldehyde ratios of lignin phenols than existing CuO oxidation methods. The microscale design (200 μL reaction volume) resulted in extremely low blanks allowing accurate and precise quantification of lignin phenols. A comparison of silica-based octadecyl-bonded sorbents (C18) with copolymer-type sorbents (PPL) indicated that sorbent type affected concentrations and diagnostic ratios of dissolved lignin phenols. For robust intercomparability of measured lignin phenol concentrations and in consideration of method detection limits for quantification, a constant sample organic carbon content of ∼30 μg C and the addition of 150 μg ascorbic acid-C are recommended. Small sample volumes avoid time-consuming extraction steps in the field, and the simplified oxidation and sample processing procedures make the new method ideal for high-throughput analysis of dissolved lignin phenols in marine and freshwater environments.

Tritium release from molten salt FLiNaK under low flux neutron irradiation with an AmBe neutron source

For examination of tritium transport in a self-cooled liquid blanket system using fluoride molten salt breeder/coolants, a series of neutron irradiation experiments have been conducted under the low flux neutron environment with an AmBe neutron source at the OKTAVIAN facility of Osaka University in Japan. Tritium release from molten salt FLiNaK (LiF-NaF-KF) at 773 K is evaluated with the neutron source, energies of which are up to 10.7 MeV and the intensity is ∼2 × 106 n/s. To measure the amount of tritium released from FLiNaK and permeating through an Inconel crucible, TF and/or T2O, and T2 are recovered separately using water bubblers and CuO oxidation beds. The amount of tritium recovered for one week in a steady state, 12.0 Bq, has closed to the calculated value, 10.6 Bq, obtained with MCNP6. More than 98% of the recovered tritium from FLiNaK has been TF and/or T2O. The overall mass transfer coefficients for tritium released from a FLiNaK free surface have been evaluated from the transient changes in recovered tritium and those are comparable to the value for HF released from FLiBe previously reported in the literature.

Corrigendum: Comparison of a simplified cupric oxide oxidation HPLC method with the traditional GC‐MS method for characterization of lignin phenolics in environmental samples

doi: 10.1002/lom3.10001 In our article entitled “Comparison of a simplified cupric oxide oxidation HPLC method with the traditional GC-MS method for characterization of lignin phenolics in environmental samples” (Limnol. Oceanogr.: Methods 13, 2015, 1–52), doi: 10.1002/lom3.10001, we would like to correct the errors in Fig. 2 and Table 2 as mentioned below. The label to Fig. 2(a) needs to be transposed as indicated in the corrected Fig. 2 image below. Entries to ∑8 value have been updated as shared below in the corrected version. Corrected Table 2 Table 2. Concentrations of CuO oxidation productsa (μg/g Sed or μg/L) of nine natural samples a Errors are standard deviations for the duplicates. b C=FAD+CAD, V=VAL+VAD+VON. c S=SAL+SAD+SON. d Ratio of VAD/VAL. e Ratio of SAD/SAL. f 890.92 µM DOC for Congo river sample. Table 2 from the published paper Table 2. Concentrations of CuO oxidation productsa (μg/g Sed or μg/L) of nine natural samples a Errors are standard deviations for the duplicates. b C=FAD+CAD, V=VAL+VAD+VON. c S=SAL+SAD+SON. d Ratio of VAD/VAL. e Ratio of SAD/SAL. f 890.92 µM DOC for Congo river sample. The authors apologize for any inconvenience this may have caused.

Lignin dynamics in secondary pasture soils of the South African Highveld

Reseeding grasses into degraded cropland and using it as permanent secondary pasture may combat desertification and promote sequestration of soil organic carbon (SOC). Our objective was to assess the contribution of lignin and grass-derived carbon to the rates of SOC accrual upon such land-use change. We sampled secondary pastures of different age (1 to 31years old), established on former degraded cropland at three agro-ecosystems in the semi-arid Highveld of South Africa; old degraded croplands and primary grassland used for cattle grazing served as controls. Topsoil samples (0–5 and 5–10cm) were characterized by their natural 13C and 15N abundances and by their contents of lignin-derived phenols (VSC) after alkaline CuO oxidation. The results showed that the δ13C signature in secondary pasture soil was variable and not a sensitive indicator of land restoration in these sites. Soil δ15N values declined from 8 to 6‰ with increased duration of secondary pasture use and approached the values of the primary grassland, suggesting that N-use efficiency improved. The VSC contents increased in the surface soils and reached a new steady-state equilibrium after 38years. Lignin sequestration was accelerated relative to total SOC in the 0–5cm soil depth but delayed in the 5–10cm soil depth, reflecting different amounts of depth-dependent inputs of plant debris into the pastures. Even if absolute VSC contents did not reach the respective concentrations in the primary grassland, the contribution of VSC to total SOC (gVSCkg−1 C) was similar to that of the primary grassland. Decreasing ratios of syringyl to vanillyl structural units reflected that after 8–19years all remaining lignin derived primarily from the new grassland vegetation. Lignin enhances SOC accumulation only in the very surface soil (0–5cm) but not below this depth, rendering the restoration of subsoil C stocks difficult in these ecosystems.

Direct Analysis of Lignin Phenols in Freshwater Dissolved Organic Matter.

A novel approach for the analysis of dissolved lignin in freshwaters is presented. Lignin concentrations in natural water samples are low, and a lignin extraction is usually required to obtain sufficient material for analysis. In this study, the alkaline CuO oxidation, which liberates a set of lignin-derived phenols, is performed directly on 15 mL of water sample in a microwave digestion system, hence reducing the required sample amount and preparation time considerably. These features make the method particularly suitable to study diagenetic changes of dissolved lignin in small-scale laboratory or field experiments. Phenol separation and quantification by gas chromatography tandem mass spectrometry lead to method detection limits between 22.7 and 1260 ng/L for single phenols, which corresponds to minimum lignin concentrations in the range of 8.5 μg/L (Σ8), offering applications for wetland, river, and lake waters with high terrestrial dissolved organic matter inputs. As a general method improvement, we present the addition of EDTA during phenol workup. EDTA binds remaining copper, thereby speeding up sample flow through the solid phase sorbent during phenol extraction and, furthermore, prevents substantial phenol losses, which occur if a water sample contains nitrate. Three natural water samples, a fresh leaf leachate and two humic-rich lake waters, were analyzed by the direct method presented here and in comparison with the established C18 extraction approach. Results show a similar reproducibility of both methods but reveal lower absolute lignin phenol yields in the humic-rich lake water samples upon C18 extraction.

Fate of carbohydrates and lignin in north-east Siberian permafrost soils

Permafrost soils preserve huge amounts of organic carbon (OC) prone to decomposition under changing climatic conditions. However, knowledge on the composition of soil organic matter (OM) and its transformation and vulnerability to decomposition in these soils is scarce. We determined neutral sugars and lignin-derived phenols, released by trifluoroacetic acid (TFA) and CuO oxidation, respectively, within plants and soil density fractions from the active layer and the upper permafrost layer at three different tundra types (shrubby grass, shrubby tussock, shrubby lichen) in the Northeast Siberian Arctic. The heavy fraction (HF; >1.6 g mL−1) was characterized by a larger enrichment of microbial sugars (hexoses vs. pentoses) and more pronounced lignin degradation (acids vs. aldehydes) as compared to the light fraction (LF; <1.6 g mL−1), showing the transformation from plant residue-dominated particulate OM to a largely microbial imprint in mineral-associated OM. In contrast to temperate and tropical soils, total neutral sugar contents and galactose plus mannose to arabinose plus xylose ratios (GM/AX) decreased in the HF with soil depth, which may indicate a process of effective recycling of microbial biomass rather than utilizing old plant materials. At the same time, lignin-derived phenols increased and the degree of oxidative decomposition of lignin decreased with soil depth, suggesting a selective preservation of lignin presumably due to anaerobiosis. As large parts of the plant-derived pentoses are incorporated in lignocelluloses and thereby protected against rapid decomposition, this might also explain the relative enrichment of pentoses with soil depth. Hence, our results show a relatively large contribution of plant-derived OM, particularly in the buried topsoil and subsoil, which is stabilized by the current soil environmental conditions but may become available to decomposers if permafrost degradation promotes soil drainage and improves the soil oxygen supply.

Carbon geochemistry of plankton-dominated samples in the Laptev and East Siberian shelves: contrasts in suspended particle composition

Abstract. Recent Arctic studies suggest that sea ice decline and permafrost thawing will affect phytoplankton dynamics and stimulate heterotrophic communities. However, in what way the plankton composition will change as the warming proceeds remains elusive. Here we investigate the chemical signature of the plankton-dominated fraction of particulate organic matter (POM) collected along the Siberian Shelf. POM (&gt; 10 µm) samples were analysed using molecular biomarkers (CuO oxidation and IP25) and dual-carbon isotopes (δ13C and Δ14C). In addition, surface water chemical properties were integrated with the POM (&gt; 10 µm) dataset to understand the link between plankton composition and environmental conditions. δ13C and Δ14C exhibited a large variability in the POM (&gt; 10 µm) distribution while the content of terrestrial biomarkers in the POM was negligible. In the Laptev Sea (LS), δ13C and Δ14C of POM (&gt; 10 µm) suggested a heterotrophic environment in which dissolved organic carbon (DOC) from the Lena River was the primary source of metabolisable carbon. Within the Lena plume, terrestrial DOC probably became part of the food web via bacteria uptake and subsequently transferred to relatively other heterotrophic communities (e.g. dinoflagellates). Moving eastwards toward the sea-ice-dominated East Siberian Sea (ESS), the system became progressively more autotrophic. Comparison between δ13C of POM (&gt; 10 µm) samples and CO2aq concentrations revealed that the carbon isotope fractionation increased moving towards the easternmost and most productive stations. In a warming scenario characterised by enhanced terrestrial DOC release (thawing permafrost) and progressive sea ice decline, heterotrophic conditions might persist in the LS while the nutrient-rich Pacific inflow will likely stimulate greater primary productivity in the ESS. The contrasting trophic conditions will result in a sharp gradient in δ13C between the LS and ESS, similar to what is documented in our semi-synoptic study.

Paddy management on different soil types does not promote lignin accumulation

AbstractPaddy soil management is generally thought to promote the accumulation of soil organic matter (SOM) and specifically lignin. Lignin is considered particularly susceptible to accumulation under these circumstances because of the recalcitrance of its aromatic structure to biodegradation under anaerobic conditions (i.e., during inundation of paddy fields). The present study investigates the effect of paddy soil management on SOM composition in comparison to nearby agricultural soils that are not used for rice production (non‐paddy soils). Soil types typically used for rice cultivation were selected, including Alisol, Andosol and Vertisol sites in Indonesia (humid tropical climate of Java) and an Alisol site in China (humid subtropical climate, Jiangxi province). These soil types represent a range of soil properties to be expected in Asian paddy fields. All upper‐most A horizons were analysed for their SOM composition by solid‐state 13C nuclear magnetic resonance (NMR) spectroscopy and for lignin‐derived phenols by the CuO oxidation method. The SOM composition was similar for all of the above named parent soil types (non‐paddy soils) and was also not affected by paddy soil management. A substantial proportion (up to 23%) of the total aryl‐carbon in some paddy and non‐paddy soils was found to originate from condensed aromatic‐carbon (e.g., charcoal). This may be attributed to the burning of crop residues. On average, the proportion of lignin was low and made up 20% of the total SOM, and showed no differences between straw, particulate organic matter (POM), and the bulk soil material. The results from CuO oxidation are consistent with the data obtained from solid‐state 13C NMR spectroscopy. The extraction of lignin‐derived phenols revealed low VSC (vanillyl, syringyl, cinnamyl) values for all investigated soils in a range (4 to 12 g kg−1 OC) that was typical for agricultural soils. In comparison to adjacent non‐paddy soils, the data do not provide evidence for a substantial accumulation of phenolic lignin‐derived structures in the paddy soils, even for those characterized by higher organic carbon (OC) contents (e.g., Andosol‐ and Alisol (China)‐derived paddy soils). We conclude that the properties of the parent soil types are more important for the lignin content of the soils than the effect of paddy management itself.

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO.

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu2O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu2O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu2O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu2O interface. Optimization of AP-SALD conditions as well as keeping Cu2O away from air and moisture in order to minimize Cu2O surface oxidation led to improved device performance. A three-fold increase in the open-circuit voltage (up to 0.65 V) and a two-fold increase in the short-circuit current density produced solar cells with a record 2.2% power conversion efficiency (PCE). This PCE is the highest reported for a Zn1-xMgxO/Cu2O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu2O-based photovoltaics.

Improved Heterojunction Quality in Cu&lt;sub&gt;2&lt;/sub&gt;O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited &lt;br /&gt;Zn&lt;sub&gt;1-x&lt;/sub&gt;Mg&lt;sub&gt;x&lt;/sub&gt;O

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu2O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu2O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu2O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu2O interface. Optimization of AP-SALD conditions as well as keeping Cu2O away from air and moisture in order to minimize Cu2O surface oxidation led to improved device performance. A three-fold increase in the open-circuit voltage (up to 0.65 V) and a two-fold increase in the short-circuit current density produced solar cells with a record 2.2% power conversion efficiency (PCE). This PCE is the highest reported for a Zn1-xMgxO/Cu2O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu2O-based photovoltaics.

Lignin biomarkers signatures of common plants and soils of Eastern Canada

Lignin CuO oxidation byproducts have been successfully used as biomarkers to describe terrigenous organic matter (TOM) dynamics in the environment in particular to understand various pedological processes. The fact that the major lignin biomarkers data-set used in environmental studies in temperate zones across the globe is based on pure vegetal samples from the Northwestern U.S.A. constitutes a major drawback in this field of research. This study presents a new lignin biomarker data-set of common plant species and soil types from the forest domain of Eastern Canada. Our results show that lignin signatures in pure vegetal samples can be significantly different from those listed as references in the literature for the same plant type (angiosperm/gymnosperm) demonstrating that location is a crucial parameter to consider. We also present characteristic lignin signatures of boreal soils that have evolved from the taxon of tree that grow on such soils. Some watershed specificities such as the presence of Sphagnum can increase the difficulty to decipher lignin sources. Specifically determining lignin signatures for pure plants and corresponding soils in a region of study is recommended to effectively use lignin biomarkers to study TOM dynamics at the watershed scale of that region.

Biochar amendment altered the molecular-level composition of native soil organic matter in a temperate forest soil

Environmental contextBiochar amendment in soil can sequester carbon but may also stimulate microbial activity, potentially enhancing soil organic matter degradation. We incubated biochar in a temperate forest soil and characterised the soil organic matter composition using molecular-level biomarker and nuclear magnetic resonance techniques. Biochar amendment altered the native soil organic matter composition and decreased the concentration of easily degradable soil organic matter components. AbstractBiochar amendment in soil can sequester carbon and improve soil water and nutrient retention, fertility and plant productivity. However, biochar may stimulate microbial activity, leading to priming or accelerated soil organic matter (OM) degradation, which could alter the native soil OM molecular composition. To investigate this, we amended sugar maple wood biochar (pyrolysed at 500°C) at four concentrations (0, 5, 10 and 20 metric tons per hectare) in a temperate forest soil for 32 weeks. Solvent extraction and CuO oxidation were used to characterise free compounds and lignin-derived phenols respectively at 8 week intervals, while base hydrolysis was used to examine plant wax, cutin and suberin components at the end of the incubation. Stimulated soil microbial activity following an adaptation period (16 weeks) resulted in increased inputs of microbial- and plant-derived soil OM components including solvent-extractable short-chain n-alkanols and n-alkanoic acids, long-chain n-alkanes and n-alkanols, and sugars. Degradation parameters for base-hydrolysable cutin- and suberin-derived compounds did not show any significant degradation of these plant biopolymers. Analysis of lignin-derived phenols revealed lower concentrations of extractable phenols and progressive oxidation of syringyl and vanillyl phenols at higher biochar application rates over time. Solution-state 1H nuclear magnetic resonance analysis of base-extractable soil OM after 32 weeks showed a decrease in the proportion of labile OM components such as carbohydrates and peptides and a relative increase in more recalcitrant polymethylene OM constituents in the amended soils. The biochar-mediated shifts in soil OM composition and reduction in labile carbon may reduce soil fertility in biochar-amended systems with long-term amendment.

Lignin phenols derivatives in lichens

Lignin monophenols have been measured in the cupric oxide oxidation products from lichens of different systematic groups. It is shown for the first time that syringyl structures in most lichens strongly dominate over vanillyl and p-hydroxyl ones (S/V 7-583, S/P 3-30). This distinguishes lichens from algae and mosses (p-hydroxyl phenols are dominant) and from higher plants (S/V ratios are from 0 in gymnosperms to 1.1-5.2 in angiosperms). Molecular ratios of phenols as well as the ratios of acids to aldehydes in lichens were different from lignin of higher plants, suggesting contribution of non-lignin phenols in CuO oxidation products. The contents of syringyl and vanillyl phenols in some lichen species were comparable to non-woody tissues of higher plants. Results of the study suggest that lichens can be important source of aromatic structures in soils and hydrosphere, particularly in the regions were lichens are abundant.

Determination of Sources of Organic Matter in Solid Waste by Analysis of Phenolic Copper Oxide Oxidation Products of Lignin

AbstractThe decomposition behavior of lignocellulosic materials is related to the taxonomic classes of the parent plant tissues. Thus, methods to characterize the composition of mixtures of lignocellulosic materials such as municipal solid waste (MSW) according to different taxonomic classes of plants are useful. The copper oxide (CuO) oxidation products of lignin provide molecular markers that allow for characterization of the initial plants. The objective of this study was to determine if the chemical composition of the monomers present after CuO oxidation can be used to infer information on the content of woody angiosperms (hardwood—HW), non-woody angiosperms (leaves and grasses—LG), woody gymnosperms (softwood—SW), and non-woody gymnosperms (needles—GN). Results showed that the composition of HW and SW in synthetic mixtures can be estimated from CuO oxidation products of lignin within an error of ±60% of the expected values. The high uncertainty in the estimate of composition in synthetic mixtures can...

Organic matter source and degradation as revealed by molecular biomarkers in agricultural soils of Yuanyang terrace.

Three soils with different tillage activities were collected and compared for their organic matter sources and degradation. Two soils (TD and TP) with human activities showed more diverse of chemicals in both free lipids and CuO oxidation products than the one (NS) without human activities. Branched alkanoic acids only accounted for less than 5% of lipids, indicating limited microbial inputs in all three investigated soils. The degradation of lignin in NS and TD was relatively higher than TP, probably because of the chemical degradation, most likely UV light-involved photodegradation. Lignin parameters obtained from CuO oxidation products confirmed that woody gymnosperm tissue (such as pine trees) may be the main source for NS, while angiosperm tissues from vascular plant may be the predominant source for the lignins in TD and TP. Analysis of BPCAs illustrated that BC in NS may be mainly originated from soot or other fossil carbon sources, whereas BC in TD and TP may be produced during corn stalk and straw burning. BC was involved in mineral interactions for TD and TP. The dynamics of organic matter needs to be extensively examined for their nonideal interactions with contaminants.

Evaluation of Copper Oxide Oxidation for Quantification of Lignin in Municipal Solid Waste

Abstract The ability to quantify lignin is an important tool for characterizing the extent of decomposition of municipal solid waste (MSW). Traditionally, acid insoluble Klason lignin (KL) has been used to measure lignin. However, synthetic organic materials such as plastics and rubber present in MSW interfere with the traditional KL method, resulting in artificially high measurements. Another method for lignin analysis is CuO oxidation, in which lignin is oxidatively hydrolyzed into phenolic monomers that are quantified by high-performance liquid chromatography or gas chromatography–mass spectrography. The objective of this study was to evaluate the applicability of CuO oxidation to measure the lignin content of MSW. The study demonstrated that analysis of lignin monomers can be simplified by skipping the ethyl acetate extraction step and that ball milling is not necessary to optimize CuO oxidation. Neither the MSW components (e.g., plastics and metals) nor extractives affected CuO oxidation. The ratio o...

Analysis of alkaline CuO degradation products of acid detergent fiber from tobacco leaves by using liquid chromatography

The acid detergent fiber (ADF) from tobacco leaves was obtained by treating the sample with petroleum ether-ethanol (6:4, v/v), 30 g/L sodium dodecylsulfate and 0.5 mol/L sulphuric acid containing 20 g/L hexadecyl trimethyl ammonium bromide successively. The ADF was degraded by the alkaline CuO oxidation procedure. In this work, six samples of ADF degradation products from tobacco leaves were prepared. The samples were analyzed by using gradient liquid chromatography (LC) where an Ultimate XB C18 column was used as stationary phase, with a mixture of methanol and water as mobile phase, at a column temperature of 35 °C and a flow rate of 0.8 mL/min. Dual wavelengths of 280 nm and 320 nm were chosen for the detection. It was found that there were four characteristic peaks for the ADF degradation products. By taking these peaks as research object, the optimum time for the degradation was found to be 5 h and the sample solution could be kept stable within 7 days. The established method may provide a new approach for the studies of the differences between lignin composition in different tobacco leaves and the relationship between lignin content and the smoking quality of tobacco leaves.

A comparison of a simplified cupric oxide oxidation HPLC method with the traditional GC‐MS method for characterization of lignin phenolics in environmental samples

AbstractA simplified method to characterize the lignin phenolic composition of environmental samples using alkaline CuO oxidation, solid‐phase extraction (SPE), and high performance liquid chromatography (HPLC) is described. Samples were oxidatively hydrolyzed in inexpensive, commercially available Teflon vials rather than expensive high‐pressure Teflon‐lined reaction vessels. We used milder hydrolysis conditions than conventionally used to avoid “over‐oxidation.” The monomeric lignin phenols released were extracted by SPE rather than liquid–liquid extraction and analyzed by reverse phase HPLC with ultraviolet (UV)‐visible diode array detection. Recoveries were 88% ± 6% for the overall procedure. The lignin phenolic composition of a wide variety of samples including plant tissues, isolated humic substances, soils, sediments, and freshwater dissolved organic matter are presented and compared with the conventional high pressure reaction vessel gas chromatography–mass spectrometry (GC‐MS) method. The agreement was generally good; the mean difference of nine diverse samples for a total of eight oxidation products was 4.5% with a relative standard deviation (RSD) of 23%. The advantages of this simplified method include no lengthy clean‐up and derivatization steps, no specialized reaction equipment, increased sample throughput, amenability to compound‐specific isotope analyses, and lower cost.

Contrasting regimes for organic matter degradation in the East Siberian Sea and the Laptev Sea assessed through microbial incubations and molecular markers

Compositional studies of organic matter on the East Siberian Arctic Shelf (ESAS) suggest that different terrestrial carbon pools have different propensities for transport and/or degradation. The current study combined laboratory-based microbial degradation experiments with earlier published degradation-diagnostic composition of several classes of terrestrial biomarkers on the same sediments to investigate differences and driving forces of terrestrial organic matter (TerrOM) degradation in two biogeochemically-contrasting regimes of the ESAS.The incubation-based anaerobic degradation rates were consistently higher (by average factor of 6) in the East Siberian Sea Kolyma Paleoriver Channel (ESS-KPC) (15μmolCO2gOC−1day−1) compared to the Laptev Sea Buor-Khaya Bay (LS-BKB) (2.4μmolCO2gOC−1day−1).The reported molecular markers show similarities between the terrestrial carbon pools in the two systems, but impose contrasting degradation regimes in combination with the incubation results. For the LS-BKB, there was a strong relationship between the degradation rates and the three lignin phenol-based degradation proxies (r2=0.93–0.96, p<0.01, linear regression) and two wax lipid-based degradation proxies (r2=0.71 and 0.66, p<0.05, linear regression). In contrast, for the ESS-KPC system, there was no relationship between incubation-based degradation rates and molecular marker-based degradation status of TerrOM. A principal component analysis indicated that short-chain fatty acids and dicarboxylic acids from CuO oxidation are mainly of terrestrial origin in the LS-BKB, but mainly of marine origin in the ESS-KPC. Hence, the microbial degradation in the western (LS-BKB) system appears to be fueled by TerrOM whereas the eastern (ESS-KPC) system degradation appears to be driven by MarOM. By combining molecular fingerprinting of TerrOM degradation state with laboratory-based degradation studies on the same ESAS sediments, a picture evolves of two distinctly different modes of TerrOM degradation in different parts of the ESAS system.