Molecular features of organic matter in diagnostic horizons from andosols as seen by analytical pyrolysis

Andosols are usually formed from volcanic substrates, with thick A horizons high in organic carbon mainly in the form of stabilized humic fractions. The peculiar properties of these soils are, to large extent, affected by poorly crystalline materials like allophanes, imogolite and other Fe and Al oxyhydroxides that induce intense organo-mineral interactions which are considered to play a relevant role in OM protection against biodegradation as regards other soils developed under similar climatic conditions. Little is known about the molecular composition of this stabilized OM in a soil scenario often considered as an efficient C-sink in terms of C sequestration processes.Whole soil samples in addition to isolated humic and fulvic acids from organic A horizons of three soils with andic properties and one non-andic soil (Sodic Cambisol) from the island of Tenerife (Canary Islands, Spain) were analysed by double shot pyrolysis-gas chromatography–mass spectrometry (Py-GC/MS) in order to get some insight on the molecular composition of different structural domains of progressive structural stability.Clear differences were found between soils, both in thermal desorption and pyrolysis behaviour of humic substances. In general the results suggest large yields of aliphatic (both alkyl and carbohydrate-derived pyrolysis compounds) pointing to high-performance processes of incorporation of aliphatic humic constituents in andosols probably favoured by interactions with amorphous minerals, whereas in non-andic soils the latter are comparatively less stabilized and are removed in early pyrolysis stages as if they occurred as loosely joined, thermoevaporation-released products.In fact, compared to Cambisol, humic and fulvic acids from andic soils led to comparatively richer pyrograms and compound assemblages. The lack of similar amounts of these loosely joined, mainly aliphatic structures after thermal desorption of the whole andic soils indicate an origin for humic substances based on rapid sequestration of C-forms of recent (litter or microbial) origin.     

Determination of dissolved organic matter based on UV-light induced reduction of ionic silver to metallic nanoparticles by humic and fulvic acids

We describe a novel solution-based method for the determination of dissolved organic matter (DOM) relying on the formation of silver nanoparticles (AgNPs) via photo-stimulated reduction of silver ions by humic and fulvic acids. The method is based on natural driven formation of nanoscale materials yielding a direct relationship between DOM concentration and AgNPs formation. The aqueous dispersion of the formed AgNPs show strong and uniform UV–Vis absorption bands between 450 and 550 nm irrespectively of DOM nature and properties (i.e. humic or fulvic acids). The ensuing chromatic shift accompanying the appearance of the new absorption bands is easily conceivable by a simple spectrophotometer and the bare eye, holding great promise for the on-site, instrumental-free screening of DOM levels. Under the optimum experimental conditions the determination of DOM was successfully demonstrated to various water samples with high sensitivity (<1.0 mg L⁻¹), satisfactory recoveries (87.5–123.5%) and reproducibility (5.87–6.73%).     

Determination of molecular formulas of natural organic matter molecules by (ultra-) high-resolution mass spectrometry: Status and needs

Electrospray ionization (ESI) combined with ultra-high-resolution mass spectrometry on a Fourier transform ion cyclotron resonance mass spectrometer has been shown to be a very powerful tool for the analysis of fulvic and humic acids and of natural organic matter (NOM) at the molecular level. With this technique thousands of ions can be separated from each other and their m/z ratio determined with sufficient accuracy to allow molecular formula calculation. Organic biogeochemistry, water chemistry, and atmospheric chemistry greatly benefit from this technique. Methodical aspects concerning the application of Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) to NOM isolated from surface water, groundwater, marine waters, and soils as well as from secondary organic aerosol in the atmospheric are reviewed. Enrichment of NOM and its chromatographic separation as well as possible influences of the ionization process on the appearance of the mass spectra are discussed. These steps of the analytical process require more systematic investigations. A basic drawback, however, is the lack of well defined single reference compounds of NOM or fulvic acids. Approaches of molecular formula calculation from the mass spectrometric data are reviewed and available graphical presentation methods are summarized. Finally, unsolved issues that limit the quality of data generated by FTICR-MS analysis of NOM are elaborated. It is concluded that further development in NOM enrichment and chromatographic separation is required and that tools for data analysis, data comparison and data visualization ought to be improved to make full use of FTICR-MS in NOM analysis.     

Fluorescence analysis of humic and fulvic acids from two Brazilian oxisols as affected by biosolid amendment

Conventional monodimensional fluorescence spectroscopy in the emission, excitation, and synchronous-scan modes and total luminescence spectroscopy have proven to be sensitive techniques for characterization and differentiation of humic acid (HA) and fulvic acid (FA) fractions isolated from an aerobically and anaerobically digested and limed biosolid, two layers of a sandy and a clayey Brazilian oxisol, and the corresponding biosolid-amended soils. The spectral patterns and the relative fluorescence intensities suggest greater molecular heterogeneity, less aromatic polycondensation, and less humification of biosolid HA and FA compared with soil HA and FA. However, the differences are smaller for the FA fractions than for the HA fractions. Fluorescence properties of soil HA and FA differ slightly as a function of soil type and soil layer. Biosolid application causes a shift to shorter wavelengths of the main fluorescence peaks and marked variation of the relative fluorescence intensities of HA and FA isolated from amended soils. These results suggest that molecular components of relatively small molecular size, with a low level of aromatic polycondensation, and low degree of humification present in biosolid HA and FA are partially and variously incorporated into amended soil HA and FA. In general, these modifications seem to be smaller in HA and FA from the clayey soil layers than in those from the sandy soil layers, possibly because of protective effects exerted by clay minerals of native soil HA and FA against disturbances caused by biosolid application.     

Reducing the interference from CO2 or organic acids in ion-selective polymer membrane sensors having a field-effect transistor as internal reference element

Changes in sample concentrations of CO₂ or organic acids cause potential instabilities when polymer membranes are directly applied to the surface of ion-selective field-effect transistors (ISFETs). Currently used designs avoid this well-documented effect by placing a layer of aqueous buffer between polymeric membrane and ISFET serving as internal reference element. Here, we propose another solution to the problem. In order to compensate for the effect of pH changes on the ISFET threshold voltage, a double membrane is applied whose inner layer is pH-sensitive, while the outer layer exposed to the sample is a conventional ion-selective membrane. It is shown that this approach strongly reduces the earlier-mentioned interference effects.     

Characterization of humic acids in sediments from dam reservoirs by pyrolysis-gas chromatography/mass spectrometry using tetramethylammonium hydroxide: Influence of the structural features of humic acids on iron(II) binding capacity

The structural features of humic acids (HAs) isolated from sediments on the bottom of dam reservoirs that can affect their binding capacities for Fe(II) were investigated by pyrolysis-gas chromatography/mass spectroscopy using tetramethylammonium hydroxide (TMAH-py-GC/MS). The binding capacities for Fe(II) increased with increasing O/C molar ratio, suggesting that the oxygen-containing functional group content plays a role in the binding of Fe(II). However, it was not possible to identify specific binding-sites for Fe(II) by TMAH-py-GC/MS analysis. Although C_16:1ω7, iso-C_15:0 and anteiso-C_17:0 fatty acids, which serve as molecular markers of anaerobic microbial activity, were detected in all of the HA samples, the contents of these acids were not correlated with binding capacities for Fe(II). However, the ratio of C_16:0 to C_16:1ω7 fatty acids, which is used as an index of anaerobic bacterial activity, increased with increasing Fe(II) binding capacities of the HAs. It thus appears likely that the activities of anaerobic bacteria on the bottom of dam reservoirs contribute to alterations in the structural features for HAs, and that this process results in increased binding capacities for Fe(II).     

Sustainability of biodiesel production in Malaysia by production of bio-oil from crude glycerol using microwave pyrolysis: a review

Biodiesel being one of the most promising renewable biofuels has seen rapid increase in production capacity due to high demand for diesel replacement; along with oversupply of its by-product, crude glycerol. Developing new industrial usage for glycerol is essential to defray the cost and sustainability of biodiesel industry and to promote the biodiesel industrialization. One of the approaches is by the transformation of glycerol into a liquid, referred as bio-oil through pyrolysis technology. Bio-oils produced by pyrolysis processes can be upgraded to produce transportation fuels or for power generation. However, current state of pyrolysis technologies are still major hurdles their development with respect to its commercial applications. Recently, microwave technology has attracted considerable attention as effective method for significantly reducing reaction time, improving the yields and selectivity of target products. Hence, this review strives extensively towards addressing the application of microwave-assisted technology applied to the pyrolysis process as a way of cost-effective and operationally feasible processes to directly utilize crude glycerol. The present review will focus on the pyrolyzed liquid product (bio-oil) derived by employing the microwave-assisted pyrolysis method. This review concludes that microwave-assisted glycerol conversion technology is a promising option as an alternative method to conventional glycerol conversion technology.     

Large‐scale Enrichment of Sulfur‐containing Acid in Acetonitrile Using Triazine Analog as the Derivatizing Reagent for Desorption from Humic‐fraction‐modified Silica Gel

The analog of triazine is used as the derivatizing reagent for enriching large‐scale acid (e.g. amino acid) containing a sulfur atom on the humic‐fraction‐modified silica gel in acetonitrile and desorbing from the adsorbent in hexane, respectively. The percent yield of the chemical derivatization under alkaline conditions, ranging from about 8 to almost 100 %, is pH dependent, and varies significantly among these examined analytes, believed to be due to the structure of the analyte, not the derivatizing reagent. The percentage of enrichment, not reproducible under an aqueous environment and independent of the type of triazine analogs, reaches almost 100 % in all cases. The force leading to the adsorption is the complexation between carboxyl groups on analyte and a humic‐fraction‐modified adsorbent based on the adsorption equilibrium results. Consequently, these results are not reproducible under ethyl ether or methanol environments due to the competition for binding sites from solvent molecules.     

Determination of organic acids in aerosol particles from a coniferous forest by liquid chromatography-mass spectrometry

LC-MS methods with use of ion-trap and time-of-flight mass spectrometers were developed for the determination of organic acids in aerosol samples collected by a high-volume sampler in a Finnish coniferous forest. Comparison was made of the composition of samples collected during atmospheric formation of new aerosol particles and on days when this formation did not occur. A dynamic sonication-assisted solvent extraction system was developed for fast and quantitative extraction of the filter samples. Several organic acids, including pinonic acid, pinic acid, and homologous series of n-alkanoic acids, n-alkenoic acids, and aliphatic dicarboxylic acids, were identified. In samples collected between 08:00 and 16:00 hours the concentration of pinonic acid ranged from 0.5 ng m(-3) to 3.7 ng m(-3) and that of pinic acid from 0.2 ng m(-3) to 1.5 ng m(-3). For most of the compounds identified, the trends in concentration could be explained by the differences in temperature during collection. However, concentrations of short-chain n-alkanoic acids were clearly higher on the days when new aerosol particle formation occurred.     

Molecular evaluation of soil organic matter characteristics in three agricultural soils by improved off-line thermochemolysis: The effect of hydrofluoric acid demineralisation treatment

The molecular composition of soil organic matter (SOM) in three agricultural fields under different managements, was evaluated by off-line thermochemolysis followed by gas chromatography mass spectrometry analysis (THM-GC-MS). While this technique enabled the characterization of SOM components in coarse textured soil, its efficiency in heavy textured soils was seriously affected by the interference of clay minerals, which catalyzed the formation of secondary artifacts in pyrolysates. Soil demineralization with hydrofluoric acid (HF) solutions effectively improved the reliable characterization of organic compounds in clayey soils by thermochemolysis, while did not alter significantly the results of coarse textured soil. A wide range of lignin monomers and lipids molecules, of plant and microbial origin, were identified in the pyrograms of HF treated soils, thereby revealing interesting molecular differences between SOM management practices. Our results indicated that clay removal provided by HF pretreatment enhanced the capacity of thermochemolysis to be a valuable and accurate technique to study the SOM dynamics also in heavy-textured and OC-depleted cultivated soils.     

Characterization of selected organic compound classes in secondary organic aerosol from biogenic VOCs by HPLC/MS<Superscript><Emphasis Type="Italic">n</Emphasis></Superscript>

The formation of secondary organic aerosols (SOA) has been investigated intensively during the last two decades in numerous field and laboratory studies and a general understanding exists about the major particle-phase products. However, recent studies show that several new product classes, such as esters, peroxides or organosulfates, also have to be considered in order to understand the detailed chemical mechanisms leading to SOA as well as to predict the aerosol mass loadings. For the identification and quantification of these three compound classes as well as for carboxylic SOA compounds, liquid chromatography (LC)/mass spectrometry (MS) is the most appropriate analytical method. In this article we try to summarize briefly the work that has been done for the determination of SOA-related carboxylic acids and we present new LC/tandem MS results on the characterization of esters, peroxides and organosulfates. In contrast to earlier work, the mass-spectrometric characterization of the individual compounds is always based on the comparison with authentic reference compounds.     

Structure of Framework Aluminum Lewis Sites and Perturbed Aluminum Atoms in Zeolites as Determined by 27Al{1H} REDOR (3Q) MAS NMR Spectroscopy and DFT/Molecular Mechanics

Zeolites are highly important heterogeneous catalysts. Besides Brønsted SiOHAl acid sites, also framework Al_FR Lewis acid sites are often found in their H‐forms. The formation of Al_FR Lewis sites in zeolites is a key issue regarding their selectivity in acid‐catalyzed reactions. The local structures of Al_FR Lewis sites in dehydrated zeolites and their precursors—“perturbed” Al_FR atoms in hydrated zeolites—were studied by high‐resolution MAS NMR and FTIR spectroscopy and DFT/MM calculations. Perturbed framework Al atoms correspond to (SiO)₃AlOH groups and are characterized by a broad ²⁷Al NMR resonance (δ_i=59–62 ppm, C_Q=5 MHz, and η=0.3–0.4) with a shoulder at 40 ppm in the ²⁷Al MAS NMR spectrum. Dehydroxylation of (SiO)₃AlOH occurs at mild temperatures and leads to the formation of Al_FR Lewis sites tricoordinated to the zeolite framework. Al atoms of these (SiO)₃Al Lewis sites exhibit an extremely broad ²⁷Al NMR resonance (δ_i≈67 ppm, C_Q≈20 MHz, and η≈0.1).     

离子色谱法测定合成气制烯烃产物中的C_1~C_6有机酸

采用离子色谱建立了合成气制烯烃(SGTO)水相产物和油相产物中C1~C6有机酸的测定方法。对分离条件进行了优化,使用标准样品测定了线性范围和工作曲线,考察了方法的精密度和准确度,确定了SGTO油相产物样品的碱洗条件,并对SGTO水相产物和油相产物样品进行了测定。结果表明:C1~C6有机酸的质量浓度在各自配制的质量浓度范围内呈现良好的线性关系,相关系数均大于0.99。标准溶液的回收率测定表明回收率在95.6%~104.3%之间,5次重复测定的相对标准偏差(RSD)在0.4%~3.6%之间,表明该方法具有良好的准确性和精密度。SGTO油相产物中的加标回收率在91.1%~96.8%之间,5次重复测定的RSD为0.7%~2.3%,准确性可以满足实际分析的需要。实际SGTO水相产物和油相产物中C1~C6有机酸的分析结果表明,SGTO水相产物中C2~C4有机酸含量较高,而SGTO油相产物中C4~C6有机酸含量较高。本研究对SGTO反应研究、催化剂制备、工艺优化以及设备材料的选择具有重要意义。     

Development of a novel environmentally friendly electrolytic system by using recyclable solid-supported bases for in situ generation of a supporting electrolyte from methanol as a solvent: application for anodic methoxylation of organic compounds

We have successfully developed a novel environmentally friendly electrolytic system using recyclable solid-supported bases for in situ generation of a supporting electrolyte from methanol as a solvent. It was found that solid-supported bases are electrochemically inactive at an electrode surface. It was also found that solid-supported bases dissociate methanol into methoxide anions and protons. Therefore, in the presence of solid-supported bases, it was clarified that methanol serves as both a solvent and a supporting electrolyte generated in situ. Anodic methoxylation of various compounds with solid-supported bases was carried out to provide the corresponding methoxylated products in good to excellent yields with a few exceptions. The methoxylated products and the solid-supported bases were easily separated by only filtration, and the desired pure methoxylated products were readily isolated simply by concentration of the filtrates. The separated and recovered solid-supported bases were recyclable for several times.