Application of pyrolysis-gas chromatography/mass spectrometry to study changes in the organic matter of macro- and microaggregates of a Mediterranean soil upon heating

The heating effect on the soil organic matter (SOM) of a Mediterranean soil was studied in two fractions (macro- and microaggregates) and in two environments (soil under canopy of Quercus coccifera and bare soil between plants). Samples were heated under laboratory conditions at different temperatures (220, 380 and 500°C) to establish their effects on the SOM quality and quantity by comparison with unheated control samples (25°C). The SOM content in the soil under canopy was higher than in the bare one and in the microaggregate fractions than in the macroaggregate ones. Increasing temperatures caused, in general, the decrease of SOM content in both soils as well as in both aggregate classes. The quality of SOM was determined after extraction with 0.1 M NaOH and analysed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Obtained pyrolysates were characterized by the presence of polyphenols and other aromatic pyrolysis products (lipids, polysaccharides, proteins and lignin derivatives). Some of the products in these control samples, and furthermore the presence of black carbon (BC) markers (e.g. benzene, pyridine and toluene), confirmed the occurrence of past wildfires in the study zone. The composition of the SOM extracted from the soils heated at 220°C, was quite similar to that obtained from unheated soils. The products derived from polysaccharides and lignin, and some coming from polyphenols, were not detected in the pyrolysates of the soil heated at 380 and 500°C.     

Molecular turnover time of soil organic matter in particle‐size fractions of an arable soil

The composition and molecular residence time of soil organic matter (SOM) in four particle‐size fractions (POM >200 µm, POM 63–200 µm, silt and clay) were determined using Curie‐point pyrolysis/gas chromatography coupled on‐line to mass spectrometry. The fractions were isolated from soils, either continuously with a C₃ wheat (soil ¹³C value = ?26.4‰), or transferred to a C₄ maize (soil ¹³C value = ?20.2‰) cropping system 23 years ago. Pyrograms contained up to 45 different pyrolysis peaks; 37 (ca. 85%) were identifiable compounds. Lignins and carbohydrates dominated the POM fractions, proteins were abundant, but lignin was (nearly) absent in the silt and clay fractions. The mean turnover time (MRT) for the pyrolysis products in particulate organic matter (POM) was generally <15 years (fast C pool) and 20–300 years (medium or slow C pools) in silt and clay fractions. Methylcyclopentenone (carbohydrate) in the clay fraction and benzene (mixed source) in the silt fraction exhibited the longest MRTs, 297 and 159 years, respectively. Plant‐derived organic matter was not stored in soils, but was transformed to microbial remains, mainly in the form of carbohydrates and proteins and held in soil by organo‐mineral interactions. Selective preservation of plant‐derived OM (i.e. lignin) based on chemical recalcitrance was not observed in these arable soils. Association/presence of C with silt or clays in soils clearly increased MRT values, but in an as yet unresolved manner (i.e. ‘truly’ stabilized, or potentially still ‘labile’ but just not accessible C). Copyright © 2009 John Wiley & Sons, Ltd.     

In situ modification of pyrolysis products of macromolecules in an analytical pyrolyser

An application of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) is presented for the fast on-line testing of solid catalysts activity in upgrading pyrolysis oils and/or gases of natural and synthetic polymers. Evaluation of the chemical conversion by a catalyst is simply and quickly performed in a Py-GC/MS instrument without any modification either of the micropyrolyser or the GC inlet. The pyrolysis products evolved from the sample pass through catalyst microbeds of some mm length and the GC/MS analysis of the converted products is performed on-line. Modification of polyolefin, styrene copolymer, polyester, polyamide, brominated epoxy resin and wood pyrolysate was carried out applying sodium type zeolite and medium acidic mesoporous aluminosilicate in the microbeds. The primary pyrolysis products are converted over the microbeds due to the catalytic activity of the bed material. Intramolecular hydrogen transfer reactions promoted by Na zeolite results in the isomerisation of alkenes and alkadienes evolved by pyrolysis from polyethylene and polypropylene. These basic catalysts were found to be effective for the elimination of brominated phenols from the pyrolysate of brominated epoxy resin. Cracking of alkane and alkene oligomer products of polyolefins to light isoalkenes occur over acidic mesoporous aluminosilicate. Certain compounds with polar groups evolved from polyester, polyamide, cellulose or lignin are removed by this catalyst. Alkenylaromatic compounds are simultaneously hydrogenated and polyaromatised in pyrolysis oils of styrene copolymers over both acidic and basic aluminosilicate catalysts tested.     

<Superscript>13</Superscript>C NMR and mass spectrometry of soil organic matter

Liquid state, high resolution ¹³C NMR spectroscopy and mass spectrometry were used to study the composition and structure of soil organic matter (SOM) using soil extracts from two long-term experiments at the Rothamsted Experimental Station. Both one- and two-dimensional NMR techniques were applied. ¹³C NMR sub-spectra of the CH _n (n=0...3) groups, obtained by the Distortionless Enhancement by Polarisation Transfer (DEPT) technique, were used for the elucidation of the qualitative and quantitative composition of humic and fulvic acids in the soils. The chemical structure of SOM was further analysed at the molecular level through Fast Atom Bombardment Mass Spectrometry (FABMS) and Gas Chromatography-Mass Spectrometry (GC/MS). Humic and fulvic extract results were not only compared to each other, but also to the solid state ¹³C NMR results for the complete soil sample.     

Characterization of soil organic matter fractions from grassland and cultivated soils via C content and delta13C signature

Variations in (13)C natural abundance and distribution of total C among five size and density fractions of soil organic matter, water soluble organic C (WSOC) and microbial biomass C (MBC) were investigated in the upper layer (0-20 cm) of a continuous grassland soil (CG, C(3) vegetation), a C(3)-humus soil converted to continuous maize cultivation (CM, C(4) vegetation) and a C(3)-humus soil converted to a rotation of maize cultivation and grassland (R). The amounts of WSOC and MBC were both significantly larger in the CG than in the CM and the R. In the three soils, WSOC was depleted while MBC was enriched in (13)C as compared with whole soil C. The relative contributions to the total C content of C stored in the macro-organic matter and in the size fraction 50-150 microm decreased with decreasing total C contents in the order CG > R > CM, while the relative contribution of C associated with the clay- and silt-sized fraction <50 microm increased. This reflects a greater stability and physical protection against microbial degradation associated with soil disruption (tillage) of the clay- and silt-associated organic C, in relation to the organic C in larger size fractions. The size and density fractions from the CG soil showed significant differences in (13)C enrichment, indicating different degrees of microbial degradation and stability of soil organic C associated with physically different soil organic matter (SOM) fractions. Delta(13)C analysis of the size and density fractions from CM and R soils reflected a decreasing turnover rate of soil organic C with increasing density among the macro-organic matter fractions and with decreasing particle size.     

Gas chromatography/mass spectrometry for the characterization of organic materials in frescoes of the Monumental Cemetery of Pisa (Italy)

The paper deals with the application of two analytical procedures, based respectively on on-line pyrolysis in the presence of hexamethyldisilazane followed by gas chromatography/mass spectrometric analysis (Py/GC/MS) and on selective extractions and microwave-assisted hydrolysis followed by GC/MS determination. These procedures give reliable data on the organic composition of micro-samples; moreover, when applied to the same micro-sample, they give comparable data on natural substances, and complementary information on synthetic compounds and degradation products. The two methods were used to characterise the organic matter present in several samples taken from scenes of the frescoes 'Giudizio Universale' and the 'Ascensione' by Bonamico Buffalmacco in the Monumental Cemetery of Pisa. The observed hydrophobicity of their surfaces, which hampers traditional means of restoration, is explained by the formation of a polymeric network due to reactions between a synthetic polymer used as adhesive, the proteinaceous material (animal glue and casein), and formaldehyde.     

The co-pyrolysis of flame retarded high impact polystyrene and polyolefins

The co-pyrolysis of brominated high impact polystyrene (Br-HIPS) with polyolefins using a fixed bed reactor has been investigated, in particular, the effect that different types of brominated aryl compounds and antimony trioxide have on the pyrolysis products. The pyrolysis products were analysed using FT-IR, GC–FID, GC–MS, and GC–ECD. Liquid chromatography was used to separate the oils/waxes so that a more detailed analysis of the aliphatic, aromatic, and polar fractions could be carried out. It was found that interaction occurs between Br-HIPS and polyolefins during co-pyrolysis and that the presence of antimony trioxide influences the pyrolysis mass balance. Analysis of the Br-HIPS + polyolefin co-pyrolysis products showed that the presence of polyolefins led to an increase in the concentration of alkyl and vinyl mono-substituted benzene rings in the pyrolysis oil/wax resulting from Br-HIPS pyrolysis. The presence of Br-HIPS also had an impact on the oil/wax products of polyolefin pyrolysis, particularly on the polyethylene oil/wax composition which converted from being a mixture of 1-alkenes and n-alkanes to mostly n-alkanes. Antimony trioxide had very little impact on the polyolefin wax/oil composition but it did suppress the formation of styrene and alpha-methyl styrene and increase the formation of ethylbenzene and cumene during the pyrolysis of the Br-HIPS.     

Prediction of Klason lignin and lignin thermal degradation products by Py–GC/MS in a collection of Lolium and Festuca grasses

A rapid method for the analysis of biomass feedstocks was established to identify the quality of the pyrolysis products likely to impact on bio-oil production. A total of 15 Lolium and Festuca grasses known to exhibit a range of Klason lignin contents were analysed by pyroprobe–GC/MS (Py–GC/MS) to determine the composition of the thermal degradation products of lignin. The identification of key marker compounds which are the derivatives of the three major lignin subunits (G, H, and S) allowed pyroprobe-GC/MS to be statistically correlated to the Klason lignin content of the biomass using the partial least-square method to produce a calibration model. Data from this multivariate modelling procedure was then applied to identify likely “key marker” ions representative of the lignin subunits from the mass spectral data. The combined total abundance of the identified key markers for the lignin subunits exhibited a linear relationship with the Klason lignin content. In addition the effect of alkali metal concentration on optimum pyrolysis characteristics was also examined. Washing of the grass samples removed approximately 70% of the metals and changed the characteristics of the thermal degradation process and products. Overall the data indicate that both the organic and inorganic specification of the biofuel impacts on the pyrolysis process and that pyroprobe–GC/MS is a suitable analytical technique to asses lignin composition.     

Quantitative comparison of the nitrogen-containing pyrolysis products and amino acid composition of soil humic acids

Pyrrole and acetonitrile, major pyrolysis products of soil humic substances, vary characteristically in abundance with the degree of humification of the organic matter in the soil. Their origin, however, is uncertain because of the large amount of unidentifiable soil nitrogen. A quantitative relationship between amino acid composition and pyrrole and acetonitrile abundances has been established by Curie-point pyrolysis-gas chromatography of a group of test proteins, using polystyrene as an internal standard. The pyrolysis yields of these products from three humic acids extracted from the surface horizons of Scottish brown forest soils (Cambisols or Ochrepts) were entirely accounted for by the known hydrolysable amino acid content and composition, and the products were related to individual amino acids. The peptide amino acid was also found to be the overall source of the aromatic pyrolysis products toluene, phenol and p-cresol.     

Analysis of Titan tholin pyrolysis products by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry

The reddish brown haze that surrounds Titan, Saturn's largest moon, is thought to consist of tholin-like organic aerosols. Tholins are complex materials of largely unknown structure. The very high peak capacity and structured chromatograms obtained from comprehensive two-dimensional GC (GC x GC) are attractive attributes for the characterization of tholin pyrolysis products. In this report, GC x GC with time-of-flight MS detection and a flash pyrolysis inlet is used to characterize tholin pyrolysis products. Identified pyrolysis products include low-molecular-weight nitriles, alkyl substituted pyrroles, linear and branched hydrocarbons, alkyl-substituted benzenes and PAH compounds. The pyrolysis of standards found in tholin pyrolysate showed that little alteration occurred and thus these structures are likely present in the tholin material.     

硫酸盐法制浆黑液中主要有机组分的热解特性研究

采用管式炉对硫酸盐法竹子、阔叶木混合制浆黑液固形物(BLS)及其三种主要组分碱木素(AL)、多糖(PLS)和木素-碳水化合物复合体(LCC),在400~800℃进行热解,全面分析了各相热解产物组成与分布规律。结果表明,BLS及其三种主要组分的热解产物组成与分布规律存在明显差异。AL、PLS和LCC对BLS热解产生H₂和CO的产率影响不大,PLS热解生成CO₂的能力明显高于BLS、AL和LCC。BLS热解液相产物中的酚类和醚类主要是来自AL和LCC;酮类和酸类是由AL、PLS和LCC共同贡献的。BLS、AL、PLS和LCC热解半焦表面形貌存在明显差异。在BLS热解过程中,AL、PLS和LCC会相互影响、相互制约,共同决定着BLS的热解特性。     

土壤有机质对菲的吸附-解吸平衡的影响

以自然土壤和过氧化氢分级土壤为实验模拟样品,测定了菲在这些样品上的吸附一解吸等温线,用线性和Freundlich模型拟合了这些等温线．^13C NMR谱表明,随着土壤有机质腐殖化程度的加深,有机质将含有较多的长链烷烃化合物,含氧、氮化合物有所减少,芳香环的数量变化不大．吸附实验结果表明,土壤有机质含量与菲的吸附容量存在一定的线性相关关系．有机质腐殖质化程度较深的样品比原土壤具有更大的吸附容量,其吸附等温线表现出更为明显的非线性,而且具有更明显的解吸滞后现象．说明土壤中一些结构紧密和含极性官能团较少的有机质是引起菲的非线性吸附过程和解吸滞后现象的主要原因。     

The three-dimensional structure of humic substances and soil organic matter studied by computational analytical chemistry

A novel three-dimensional structural concept for humic substances and soil organic matter (SOM) is proposed which is based on previously published, comprehensive investigations combining geochemical, wetchemical, biochemical, spectroscopic, agricultural and ecological data with analytical pyrolysis. Direct, temperature-programmed pyrolysis in the ion-source of the mass spectrometer and soft ionization in very high electric fields (Py-FIMS) and Curie-point pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) were the main applied thermal methods. Emphasis is laid on molecular modelling and geometry optimization of complex, polydisperse structures of biomacromolecules using modern PC software (HyperChem^®). Trapping and binding of atrazine in an organo-mineral complex is introduced as a first example of simulation experiments for soil processes at atomic level (nanochemistry). Future applications of semi-empirical calculations and molecular dynamics in pyrolysis studies are outlined.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Effect of the soil uses on their thermal stability

Differential scanning calorimetry was applied to assess on seasonally soil organic matter changes. Soils were collected in two sites located in Viveiro (Galicia, Spain). One of them has been used as arable land and the other one was under pinewood. Soil samples were seasonally collected during a year. The heat of combustion and the ignition temperature of the soil organic matter were calculated by analyzing the thermograms obtained by differential scanning calorimetry. The shape and the maximum and end temperatures of the two exothermic peaks observed in the thermograms, yielded information about the relations between the labile and recalcitrant pools, and hence information about carbon stabilization degree in both soils.     

GC和GC／MS分析脱硫细菌代谢二苯并噻吩的产物

从茂名炼油厂周围土壤中分离得到一株可脱除二苯并噻吩（DBT）的细菌YC－LI－1用GC／MS方法定性鉴定了该细菌脱除DBT的代谢的有机产物为2－羟基联苯（1－OHBP）,此外试验还证明了DBT中的硫原子代谢为水溶性的硫酸盐,用GC方法测定了该菌种将DBT代谢为2－羟基联苯的转化率,分析结果表明该菌种可有效代谢DBT,转化率达90％以上。     

Influence of recent vegetation on labile and recalcitrant carbon soil pools in central Queensland, Australia: evidence from thermal analysis-quadrupole mass spectrometry-isotope ratio mass spectrometry

The effect of a recent vegetation change (<100 years) from C(4) grassland to C(3) woodland in central Queensland, Australia, on soil organic matter (SOM) composition and SOM dynamics has been investigated using a novel coupled thermogravimetry-differential scanning calorimetry-quadrupole.mass spectrometry-isotope ratio mass spectrometry (TG-DSC-QMS-IRMS) system. TG-DSC-QMS-IRMS distinguishes the C isotope composition of discrete SOM pools, showing changes in labile, recalcitrant and refractory carbon in the bulk soil and particle size fractions which track the vegetation changes. Analysis of evolved gases (by QMS) from thermal decomposition, rather than observed weight loss, proved essential in determining the temperature at which SOM decomposes, because smectite and kaolinite clays contribute to observed weight losses. The delta(13)C analyses of the CO(2) evolved at different temperatures for bulk soil and particle size-separates showed that most of the labile SOM under the more recent woody vegetation was C(3)-derived carbon whereas the delta(13)C values in the recalcitrant SOM showed greater C(4) contributions. This indicated a shift from grass (C(4))- to tree (C(3))-derived carbon in the woodland, which was also supported by the two-phase (13)C enrichment with depth, i.e. C(3) vegetation dominated the top soil (0-10 cm), but the C(4) contribution increased with depth (more gradual). This is perturbed by the inclusion of charcoal from forest fires ((14)C age incursions) and by the deep incorporation of C(3) carbon due to root penetration.     

Py-GC/MS characterization of a wild and a selected clone of Arundo donax,and of its residues after catalytic hydrothermal conversion to high added-value products

Two analytical procedures based on gas chromatography and mass spectrometry were used to study the compositions of a wild population and a selected clone (Torviscosa) of giant reed (Arundo donax L.), one of the most promising biomass both in terms of energy and fine chemicals production. Gas chromatography/mass spectrometry (GC/MS) was used to characterize and quantitatively determine the monosaccharide composition. Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), using hexamethyldisilazane (HMDS) as a derivatising agent, was used to characterize the lignocellulosic polymers. Analytical pyrolysis was also used to study the composition of residues left after the catalytic hydrolysis used to convert cellulose to levulinic acid and hemicellulose to furfural.GC/MS allowed us to determine the monosaccharide composition and polysaccharide content of the giant reed samples, highlighting that there was no significant difference between the wild population and the selected clone. GC/MS also highlighted that the giant reed leaves have a higher percentage (roughly 60%) of polysaccharide material than the stalks, which contain approximately 50%.Py-GC/MS, following the disappearance of the pyrolysis products of polysaccharides, showed that 150 °C and 190 °C are the best temperatures to obtain the complete catalytic conversion of hemicellulose and cellulose, respectively. Analytical pyrolysis also highlighted that in the course of catalytic hydrothermal conversion a partial depolymerisation of lignin was obtained. In particular, the formation of lignin units containing free phenol groups via the cleavage of the β-aryl ether bonds was demonstrated. The presence of these free phenols in the lignin network suggests the possible exploitation of lignin residues as antioxidant components or in high value biopolymer industries rather than the traditional use as low-value fuel for energy production.     

Use of 13C to monitor soil organic matter transformations caused by a simulated forest fire

Soil organic matter (SOM) transformations caused by heating were analyzed using the stable carbon isotope (13)C as a tracer to follow C mineralization dynamics and C transfers between different organic compartments. A (13)C-labelled soil, obtained by incorporation of (13)C-enriched Lolium perenne phytomass into a pine forest soil, was heated for 10 min at 385 degrees C to reproduce conditions typical of a forest fire and changes in total C content, potential C mineralization activity and C distribution between the different soil organic fractions were determined. Changes caused by heating on the potential soil C mineralization, determined by laboratory aerobic incubation, reveal alterations to the SOM biodegradability; some stabilized SOM showed an increase in biodegradability, whereas less stabilized SOM became more resistant to microorganisms. Chemical fractionations of SOM allowed us to monitor changes in its composition. As a consequence of heating, the less polymerized humic fractions were the most strongly affected, with the total disappearance of fulvic acids. A significant increase in the quantity and degree of polymerization of the humic acids at the expense of other more (13)C-enriched substances was also found. Finally, a large decrease in humin was observed, its solubilizable part disappearing completely, probably as a consequence of the incorporation of the byproducts into the free organic matter fraction.     

Characterization of soil carbon from a Svalbard glacier-retreat chronosequence using pyrolysis–GC/MS analysis

Pyrolysis–gas chromatography/mass spectrometry was used to compare soil carbon samples from a glacier-retreat chronosequence in the high Arctic. The analysis considered the relative abundance of different pyrolysis products in an attempt to distinguish significant shifts in the soil-C pool. The relative abundance of the compound classes, pyridines, furfurals, phenols, aromatic hydrocarbon precursors, and cyclopentanones were compared. Based on principal component analysis that explained 90% of the variance in the first and second components, the compound classes were well separated. As such, the compound classes selected were well suited for identifying differences among the samples. The most obvious change indicated the appearance of ligninaceous material in the soil-C pool. This shift appeared to occur between 60 and 100 years after glacial retreat. Another less obvious shift was the change from a largely animal dominated early colonization to algae. This shift occurred between 2 and 16 years after glacial retreat. The results suggest that pyrolysis–gas chromatography/mass spectrometry (pyrolysis–GC/MS) can be an effective tool for drawing distinctions between soil-C at different sites and relationship to cover matter.     

Relationship between soil organic C degradability and the evolution of the delta13C signature in profiles under permanent grassland

The main objective of this research was to investigate to what extent the potential C dynamics of soil organic matter (SOM) are related to the degree of 13C enrichment with increasing depth in soil profiles under permanent grassland. The evolution of the C content and the 13C natural abundance (delta13C value) of SOM were investigated in three soil profiles (0-40 cm depth) under permanent grassland of varying texture (a loamy sand, a loam and a clay loam soil). The delta13C value of the SOM showed a gradual increase with increasing depth and decreasing C content in the profiles, ranging from 1.9 per thousand (loamy sand soil), 2.9 per thousand (clay loam soil) and 4 per thousand (loam soil) in relation to the delta13C value of SOM at the surface. The relationship between the 13C enrichment and total organic C content at different depths in the profiles (down to 40 cm depth in the loam and clay loam soil, down to 25 cm depth in the loamy sand soil) could be well described by the Rayleigh equation. The enrichment factors epsilon, associated with the Rayleigh approximation of the data, ranged from -1.57 per thousand (clay loam soil) to -1.64 per thousand (loamy sand soil) and -1.91 per thousand (loam soil). The potential C dynamics in four depth intervals from the profiles (0-10, 10-20, 20-30 and 30-40 cm depth) were determined by means of an incubation experiment. The C decomposition rate constants from the four sampling depths in the profiles showed a significant, positive correlation (y = 0.21x + 0.018, R(2) = 0.66, p < 0.005) with the corresponding Deltadelta13C values (change of the delta13C value per depth increment). A better correlation was obtained when only the data from the upper 20 cm in the profiles (y = 0.21x + 0.019, R(2) = 0.78, p < 0.05) were considered. These results suggest that the Deltadelta13C values in the surface layers of profiles under permanent grassland may serve as an indicator of the potential degradability or the stability of the SOM (in terms of C decomposition rate constants).