Thermally Assisted Hydrolysis And Methylation-gas Chromatography-mass Spectrometry Research Articles

Impacts of agricultural drainage on the quantity and quality of tropical peat soil organic matter in different types of forests

Tropical peatlands serve as huge carbon (C) pools in the global C balance, and degradation due to agricultural use is a major concern. The objective of the present study was to examine the relationship between the C loss rate in agriculturally drained tropical peat soils in relation to groundwater level (GWL) and the chemical structure of the resulting soil organic matter (SOM). Soil mesocosms containing three peat soils collected from three forest types in Malaysia, Mixed peat swamp (MPS), Alan Batu (ABt), and Alan Bunga (ABg) forests, which are classified based on dominant plant species, species diversity, and forest structure, were buried in an oil palm plantation for a period of five years. Soil samples packed in the top layer (0–20 cm depth) and the bottom (60–80 cm depth) layer were then analyzed and the results were compared with the initial values for these soils. Weight loss, total C and N contents, ash content, and pyrophosphate solubility index (PSI; an index of the degree of humification) were measured. Changes in the chemical structure of the SOC were investigated using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy with phase-adjusted spinning side bands and thermally assisted hydrolysis and methylation-gas chromatography/mass spectrometry (THM-GC/MS). The C loss in the MPS forest soil, 2–12%, was smaller than that in the ABt and ABg forest soils, 20–37%, especially in the bottom layer. The higher C loss in the ABt and ABg soils, without significant difference between the top and bottom layers, can be attributed to the greater accumulation of less decomposed plant components as evidenced by the larger yields of lignin-derived phenols and polysaccharide-related compounds in THM-GC/MS analysis. The C composition as estimated by 13C NMR did not vary during incubation of the ABt and ABg soils while the yields of lignin-derived and other phenols as well as polysaccharide-related compounds in THM-GC/MS were decreased, especially in the top layer. These findings suggest that plant components with a low degree of decomposition are susceptible to drainage regardless of their structure. The progression of the oxidative degradation of lignin in the top layer of all soils was also suggested by the increases in PSI and the vanillic acid/vanillin ratio. The % O-alkyl C and % alkyl C may control the rate of C loss positively and negatively, respectively. PSI also appears to be useful for roughly estimating the decomposability of tropical peat SOM in various GWLs.

Effective pretreatment for thermally-assisted hydrolysis and methylation GC-MS of intractably cross-linked acrylate copolymers

Thermally-assisted hydrolysis and methylation-gas chromatography-mass spectrometry (THM-GC-MS) using tetramethylammonium hydroxide (TMAH) is an effective approach for the characterization of condensation polymers with ester linkages such as ultraviolet (UV)-cured acrylate resins. However, for intractably cured acrylic resins, reliable structural characterization is often difficult by conventional THM-GC-MS owing to insufficient THM reactions. In this study, a pretreatment to effectively improve THM efficiency was proposed, in which the resin sample was preliminarily soaked and dissolved in a TMAH-methanol solution in a microtube. An aliquot of the TMAH solution was then introduced into the pyrolyzer at 400 °C to produce THM-GC-MS. The effectiveness of the proposed pretreatment was demonstrated using a UV-cured acrylate copolymer consisting of bulky and high-molecular weight bifunctional acrylate (9,9-Bis[4-(2-acryloyloxy ethoxy) phenyl]fluorene) and monofunctional acylate (2-(9 H-Carbazol-9-yl)ethyl acrylate) monomers, for which THM reactions did not proceed efficiently in conventional THM-GC-MS. Conversely, by the modified THM-GC-MS process with a pretreatment involving immersion at room temperature for 24 h or at 60 °C for 30 min, the characteristic decomposition products for each monomer unit were clearly observed in the chromatograms, and the copolymer composition could be precisely estimated from the relative yields of the observed decomposition products. In addition, a methyl acrylate peak, formed from unreacted acrylate moieties in the photocured copolymer, appeared in the chromatogram. Its relative yields were correlated to the double bond conversion in the cured sample. The observed results were successfully interpreted to clarify the curing process of the photocured acrylate copolymer samples.

Nontargeted Pattern Recognition in the Search for Pyrolysis Gas Chromatography/Mass Spectrometry Resin Markers in Historic Lacquered Objects.

A differential expression analysis technology developed for linear modeling of gene expression data was used in combination with thermally assisted hydrolysis and methylation gas chromatography/mass spectrometry (THM-GC/MS) to support the analysis of lacquers and varnishes on historical objects. Exudates from tropical trees, such as Manila copal, sandarac, South American copal, and Congo copal, which were frequently used in finishing layers on decorative objects up to the early 20th century, were compared through this approach. Highly discriminating features indicate biomarkers that can help to identify copals in resinous lacquers. The approach allows new, more systematic ways for finding biomarkers in the analysis of lacquered objects of art and varnishes.

An Investigation of Eighteenth-Century English Red Japanned Furniture in the Collection of The Metropolitan Museum of Art, New York

ABSTRACTThe decorative surfaces of four pieces of eighteenth-century English red japanned furniture, including a card table and side chair by Giles Grendey (1693–1780), were examined. Cross-sectional microscopy, X-ray fluorescence spectroscopy (XRF), Fourier transform infrared micro-spectroscopy (micro-FTIR), attenuated total reflectance micro-FTIR (micro-ATR-FTIR), Raman spectroscopy, thermally assisted hydrolysis and methylation-gas chromatography-mass spectrometry (THM-GC-MS) analysis, and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) were used to investigate the layer structure and material use. Analysis revealed the common use of a spirit varnish based on sandarac and turpentine, whose simple formulation is at odds with those typically suggested in period recipes for red japanning. Vermilion pigment was used for the red grounds, but different preparatory layers as well as materials for relief decoration separate Grendey’s red furniture from the other objects studied. More examples need to be examined in order to ascertain whether observations regarding process and material use reflect wider practice. However, results from this preliminary investigation suggest that japanners in England were less reliant on the recipes of the treatises than has been supposed, as well as hinting at the possibility of identifying idiosyncratic practices of particular craftsmen.

Combining thermal hydrolysis and methylation-gas chromatography/mass spectrometry with X-ray photoelectron spectroscopy to characterise complex organic assemblages in geological material

What follows is a method applicable generically to the analysis of low levels of organic matter that is embedded in either loose fine-grained or solid geological material. Initially, the range of organic compounds that could be detected in a geological sample using conventional pyrolysis chromatography/mass spectrometry was compared to the range that was detected using thermally assisted hydrolysis and methylation-gas chromatography/mass spectrometry (THM-GC/MS). This method was used to validate the synthetic components fitted to X-ray photoelectron spectroscopy (XPS) carbon spectra of the sample. Reciprocally, XPS analysis was able to identify the constituent carbon-carbon, carbon-oxygen and carbon-nitrogen bonds of the functional groups in the compounds identified by THM-GC/MS. The two independently derived outputs from the THM-GC/MS and the XPS techniques mutually validated the identification of organic compounds in our geological samples.We describe in detail the improvements to:•The preparation of geological samples for analysis by XPS.•Measurements of organic material in geological samples using GC/MS.•The use of THM-GC/MS and XPS data used together to characterise low levels of organic material in geological samples.

Characterization of high-molar-mass fractions in a Scots pine (Pinus sylvestris L.) knotwood ethanol extract

AbstractThe identification of compounds in Scots pine (Pinus sylvestrisL.) knotwood (KnW), obtained by extracting with hydrophilic organic solvents, has been performed previously almost exclusively by gas chromatography-mass spectrometry (GS-MS) equipped with long GC columns (≥25 m). That means that the molar mass (MM) of the majority of the identified compounds was below 500–600 Da, and the analytical data accounted for only about half of the dry extract weight. In the present work, high-molar-mass (HMM) fractions in a Scots pine KnW-EtOH extract were isolated and chemically characterized by means of several advanced analytical techniques, such as high performance size-exclusion chromatography-evaporative light scattering detector (HPSEC-ELSD), high performance liquid chromatography (HPLC)-electrospray ionization-ion trap-mass spectrometry [(HPLC)ESI-IT-MS], ESI-quadrupole time of flight-mass spectrometry (QTOF-MS), pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), thermally assisted hydrolysis and methylation-gas chromatography-mass spectrometry (THM-GC-MS), nuclear magnetic resonance (NMR) and GC-MS. The results indicate that the MM maxima of the HMM fractions ranged from approximately 500 to 2200 Da, and that the compounds consist mainly of oligomers of hydroxylated resin acids (RAs), especially dehydroabietic acid, but also of fatty acids (FAs), stilbenes and sterols. A large number of RA dimers were tentatively identified in the HMM fractions. However, it remains unknown how the monomer units are linked together, as it was not possible to isolate a RA dimer fraction pure enough for NMR characterization. RA dimers in native KnW have not been identified previously.

Influence of phthalocyanine pigments on the photo-degradation of alkyd artists' paints under different conditions of artificial solar radiation

The influence of selected blue and green phthalocyanine pigments on the stability of alkyd paints exposed to accelerated solar radiation is presented. Thus, paint samples were artificially aged by exposure to accelerated solar radiation, including UV-B range. The ageing was performed with Xenon Arc lamp at low (soft conditions) and at high (strong conditions) irradiance values, where the soft conditions are comparable to natural light ageing.The behaviour of alkyd paints exposed to artificial ageing was investigated after two and four months by Attenuated Total Reflection Infrared Spectroscopy (FTIR-ATR) and Thermally assisted Hydrolysis and Methylation Gas Chromatography/Mass Spectrometry (THM-GC/MS).It could be determined that the photo-degradation of the paints started already after two months of exposure under soft conditions. Paints aged under strong conditions showed comparable results when exposed for two and for four months. This indicates that samples are already highly damaged after the first two months of strong ageing and during additional two months no significant increase in photo-degradation occurs. The results showed that - independently from the ageing conditions - in both cases the ester bond of the polyester portion of the alkyd resin is affected by photo-cleavage and the presence of phthalocyanine pigments is stabilizing the paint systems against it. Nevertheless, among the tested samples, the paints containing chlorinated and brominated copper phthalocyanine green (PG36) were the most degraded.

Novel molecular proxies for inferring pyrogenic black carbon oxidation state using thermally assisted hydrolysis and methylation (THM-GC–MS) with 13C-labeled tetramethylammonium hydroxide (TMAH)

Analytical techniques to assess the degree of alteration of pyrogenic black carbon (C) in soils and sediments are needed to gauge the role of environment and time in the dynamics of this stable carbon form. The benzenecarboxylic acids (BnCA, with n=number of carboxylic groups) and naphthalene analogues (NnCA) released by thermally assisted hydrolysis and methylation (THM) of black C have the potential to yield information about black C oxidation state but it remains unclear to what extent the carboxylic groups in BnCA and NnCA are native to the sample or form as analytical artefacts during the THM reaction. In an effort to clarify the source of analytical products and investigate long term black C oxidation in a soil environment we applied THM gas chromatography mass spectrometry (THM-GC–MS) using 13C-labeled tetramethylammonium hydroxide (13C-TMAH) to oak-derived black C samples isolated from a colluvial soil profile dating to 50–8100cal BP. The results showed that the BnCA and NnCA originate from the black C and are potentially usable as oxidation proxies, with the exception of B1CA and hydroxyl-B1CA which have a significant source in lignin. The cumulative abundance of BnCA (excluding B1CA) and NnCA increased with age of the black C (P<0.05) from ca. 0.05-0.20mg/100mg organic C. Furthermore, the ratios B3CA/B2CA and (B3CA+B4CA)/B3CA increased with age, and are proposed as novel proxies of black C oxidation state. The results support previous studies showing that carboxyl functionalities dominate over hydroxyl and that molecular markers of lignin are selectively depleted within 1000 yrs after wildfire. The accumulation of hydroxyl and especially carboxyl functional groups on black C structures seems to be a gradual process that continued at least until the end of the studied ageing window of 8100 yrs.

Changes in the Quality of Chromophoric Dissolved Organic Matter Leached from Senescent Leaf Litter during the Early Decomposition

Chromophoric dissolved organic matter (CDOM) leached from leaf litter is a major source of humus in mineral soil of forest ecosystems. While their functions and refractoriness depend on the physicochemical structure, there is little information on the quality of CDOM, especially for that leached in the very early stages of litter decomposition when a large amount of dissolved organic matter (DOM) is leached. This study aimed to better understand the variations/changes in the composition of CDOM leached from senescent leaf litter from two tree species during the early stage of decomposition. Leaf litter from a conifer tree (Japanese cedar, D. Don) and a deciduous broad-leaved tree (Konara oak, Thunb.) were incubated in columns using simulated rainfall events periodically for a total of 300 d at 20°C. The quality of CDOM was investigated based on the fluorescence properties by using a combination of excitation-emission matrix fluorescence (EEM) and parallel factor analysis (PARAFAC). In addition, the phenolic composition of DOM was investigated at a molecular level by thermally assisted hydrolysis and methylation-gas chromatography-mass spectrometry (THM-GC-MS) in the presence of tetramethylammonium hydroxide (TMAH). The EEM was statistically decomposed into eight fluorescence components (two tannin/peptide-like peaks, one protein-like peak, and five humic-like peaks). A significant contribution of tannin/peptide-like peaks was observed at the beginning of incubation, but these peaks decreased quickly and humic-like peaks increased within 1 mo of incubation. The composition of humic-like peaks was different between tree species and changed over the incubation period. Since tannin-derived phenolic compounds were detected in the DOM collected after 254 d of incubation on THM-GC-MS, it was suggested that tannins partially changed its structure, forming various humic-like peaks during the early decomposition.

TG/MS, Py-GC/MS and THM-GC/MS study of the composition and thermal behavior of extractive components of Robinia pseudoacacia

The thermal behavior and composition of extractives of 1-year-old shoots of Robinia pseudoacacia (black locust) have been studied. The extractives have been eliminated from the wood samples with Soxhlet extraction using different solvents. The study of the thermal decomposition of the extracted materials has been performed with thermogravimetry/mass spectrometry (TG/MS). For the qualitative analysis of the extracted compounds pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermally assisted hydrolysis and methylation-gas chromatography/mass spectrometry (THM-GC/MS) methods have been used. The thermal behavior of the original and extracted wood samples has also been investigated with the same thermal methods. The obtained results imply that the extractives decompose in the same temperature range as the natural polymers that make up the cell walls of plants. Although the decomposition pathways of polysaccharides and lignin are not altered by the extractive compounds, the extractives evolve additional products influencing the product distribution of the whole wood samples. The comparison of extraction procedures has shown that the quality of the solvent and the extraction time significantly influence the amount of extracts eliminated from the plant sample. All the applied solvents (ethanol, acetone and dichloromethane) were capable of removing the phytosterols from the wood. However, fatty acid esters remained in the extracted wood samples in significant amounts even after successive extraction by dichloromethane, ethanol and water.

THM-GCMS and FTIR for the investigation of paints in Picasso's Still Life, Weeping Woman and Nude Woman in a Red Armchair from the Tate Collection, London

Thermally assisted hydrolysis and methylation-gas chromatography–mass spectrometry (THM-GCMS) in conjunction with Fourier transform infrared spectroscopy (FTIR) have been successfully used for the identification of different binding media, including synthetic resins and natural binders, employed by Picasso on Still Life (1914), Nude Woman in a Red Armchair (1932) and Weeping Woman (1937), works owned by the Tate, London. In particular, the results obtained prove that at certain dates Picasso experimented and likely mixed his oil paints with other compounds, such as animal fats, and at very early date he employed alkyd resins, unusual for the times.

THM-GCMS and FTIR for the study of binding media in Yellow Islands by Jackson Pollock and Break Point by Fiona Banner

Throughout the 20th century a number of binding media, including synthetic resins, have been employed in paints. It is only very recently that thermally assisted hydrolysis and methylation-gas chromatography-mass spectrometry (THM-GCMS) has been used for the identification of a wide variety of binding media employed in the 20th century art. This paper shows as THM-GCMS was successfully used in conjunction with Fourier Transform Infrared Spectroscopy for the study of binding media in samples from Yellow Islands by Jackson Pollock [Tate Collection, T00436] and Break Point by Fiona Banner [Tate Collection, T07501].

Ageing behaviour and pyrolytic characterisation of diterpenic resins used as art materials: colophony and Venice turpentine

The ageing behaviour of two diterpenic resins traditionally used as artists’ materials, colophony and Venice turpentine, was investigated with different spectroscopic and chromatographic techniques. In particular, three types of ageing (natural, artificial external conditions with a xenon lamp, artificial indoor conditions with fluorescent tubes) were applied to laboratory samples to study their effects on chemical structures. Thermally-assisted hydrolysis and methylation-gas chromatography-mass spectrometry (THM-GC/MS) was employed for careful characterisation and for identification of markers compounds on the vergin resins and in the course of ageing. The most significant changes were detected in the initial part of ageing, and the principal degradation products coming from oxidation, polymerisation and cleavage reactions identified. The high intensity of xenon lamp irradiation was found to cause, apart from oxidation and polymerisation reactions, further degradation of the chemical structure with molecular fragmentation. From the analytical point of view, the differentiation between colophony and Venice turpentine with THM-GC/MS appears to depend on differences in the lower molecular weight resin components.