Kai-Uwe Eckhardt

Characterization of different decomposition stages of biowaste using FT-IR spectroscopy and pyrolysis-field ionization mass spectrometry

The decomposition stage and stabilization of organic matter in biowaste (mixture of yard waste and kitchen waste), originating from an open windrow process, were investigated using Fourier transform infrared (FT-IR) spectroscopy and pyrolysis-field ionization mass spectrometry (Py-FIMS). These investigations provided detailed information about chemical constituents and their behavior during the composting process. The chemical compounds were classified by their molecular signals in Py-FIMS. Multivariate statistical analysis revealed, that during the composting process, the group containing lipids, fatty acids and other chemical compounds with aliphatic skeletons changed the most. Corresponding with Py-FIMS findings changes were observed in absorbance bands of infrared spectra that reflect this group of organic compounds: the aliphatic methylene bands at 2925 and 2850 cm-1, the band of C=O vibrations of carboxylates at 1640 cm-1, the O=H in-plane bend of carboxylic acids, the CO2 stretch of carboxylates and the CH2 group of alkanes at around 1430 cm-1. During decomposition these bands decreased up to a steady level that indicated stabilization. The band at 1260–1240 cm-1 that can be assigned to the C=O stretch of carboxylic acids or to the C=N stretch of amides and the band of aromatic amines at 1320 cm-1 disappeared completely. The nitrate band at 1384 cm-1 appeared at a later stage of the composting process. The relative increase of chemical compounds like moieties of lignin, humic acids and tannins in the composted material contributed to the aromatic C=C band at around 1640 cm-1.

Phosphorus L2,3‐edge XANES: overview of reference compounds

Synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy is becoming an increasingly used tool for the element speciation in complex samples. For phosphorus (P) almost all XANES measurements have been carried out at the K-edge. The small number of distinctive features at the P K-edge makes in some cases the identification of different P forms difficult or impossible. As indicated by a few previous studies, the P L(2,3)-edge spectra were richer in spectral features than those of the P K-edge. However, experimentally consistent spectra of a wide range of reference compounds have not been published so far. In this study a library of spectral features is presented for a number of mineral P, organic P and P-bearing minerals for fingerprinting identification. Furthermore, the effect of radiation damage is shown for three compounds and measures are proposed to reduce it. The spectra library provided lays a basis for the identification of individual P forms in samples of unknown composition for a variety of scientific areas.

The significance of host-fungus combinations in ectomycorrhizal symbioses for the chemical quality of willow foliage

The majority of plants interacts with mycorrhizal fungi, which predominantly provide mutual benefits, but also costs. We tested the hypothesis that specific combinations of host plants (four commercial varieties of Salix spp.) and ectomycorrhizal partners (species of Laccaria, Paxillus, Tricholoma and Hebeloma) differ in their effects on the host foliar chemistry. Twenty specific host - mycorrhiza combinations were pot-grown outdoors under low-N conditions. Foliar concentrations of total phenolics and salicylic acid were decreased by mycorrhizas in S. schwerinii x S. viminalis and S. x dasyclados genotypes, but increased in S. viminalis. Mycorrhiza effects on host biomass production were positive, indifferent or negative, depending on the specific host—mycorrhiza combination. The host plant genotype influenced mainly the direction of mycorrhizal effects on foliar chemistry, whereas the magnitude of mycorrhizal effects varied mostly among the fungal genotypes. The results are relevant with respect to the possible interactions between mycorrhizas, plants and leaf herbivores.

Composition of organic matter in particle size fractionated pig slurry.

Pig slurry is a heterogeneous mixture of different particle sizes that will have different mobility in soil. Therefore, a physically fractionated pig slurry sample was analysed, e.g. using pyrolysis-field ionisation mass spectrometry (Py-FIMS) in an effort to identify relationships between particle size and composition of organic matter. The presumably most mobile fractions in soils (<63 microm) accounted for approximately 50% of slurry dry matter and were dominated by lignins, and N-containing compounds. Sterols were especially abundant in the larger-sized fractions, which corresponds to their reported distribution in soils and surface waters. The averaged molecular masses indicated similarities of fractions <10 microm to aquatic humic substances and increasing content of plant material with increasing particle size. A statistical analysis of the compound class distribution revealed that the analysis of three particle size fractions is essential for the assessment of the composition and properties of slurry constituents.

Advances in Understanding Organic Nitrogen Chemistry in Soils Using State-of-the-art Analytical Techniques

Abstract During the past decade, soil and geochemists have adopted a variety of novel chemical–analytical methods to explore the chemistry of soil organic N (N org ). This chapter summarizes some of the more recent developments in the use of wet-chemical and instrumental methods to determine total N org concentrations as well as to speciate the N org in soils. A critical evaluation of 15 N nuclear magnetic resonance (NMR) spectroscopy found the technique to be wanting, in terms of its sensitivity and ability to identify classes of N org compounds in soils. Complementary mass spectrometric techniques are described briefly, and improved data evaluations based on broad applications of high-resolution pyrolysis-field ionization mass spectrometry are presented and discussed. A reassessment of older data sets using the new spectral evaluation algorithms provides strong evidence of fire- and management-induced changes in N org speciation. Isotope-ratio mass spectrometry, Fourier transform ion cyclotron resonance mass spectrometry, and nanoscale secondary ion mass spectrometry (Nano-SIMS) also are discussed, with the latter two techniques having potential to (1) identify N org compounds and (2) provide spatially resolved information on the molecular, elemental and isotopic composition of soil N org . The use of 15 N labeling techniques is discussed both from a methodological standpoint and in terms of tracking the fate of plant-derived (residue or rhizodeposit) N in the soil. Indeed, coupling 15 N labeling with analytical techniques such as 15 N NMR, Nano-SIMS and high- or ultrahigh-resolution mass spectrometry can provide information on how N is incorporated into soil organic matter. Analytical and instrumental innovations have resulted in new insights into the chemistry of N org —together with a revised summary of the relative amounts of the different N org compound classes present in soils (e.g. aliphatic amine and amide N, aromatic heterocyclic N), as well as their ecophysiological functions. Particular emphasis is given to the use of multitechnique analyses and the outstanding molecular–chemical diversity of biogenic heterocyclic N org compounds. Examples are given of the new insights obtained using multi-analytical research approaches to explore microbial utilization of heterocyclic N and organic–mineral interactions, as well as the ability of human and environmental intervention to alter the composition of soil N org . Finally, we examine future challenges and propose analytical approaches to tackle open questions regarding the basic chemistry and cycling of N org in soils, as well as the agronomic and environmental consequences associated with N transformations in agro-ecosystems.

Hydrothermal carbonization of biomass residues: mass spectrometric characterization for ecological effects in the soil-plant system

Hydrochars, technically manufactured by hydrothermal carbonization (HTC) of biomass residues, are recently tested in high numbers for their suitability as feedstock for bioenergy production, the bioproduct industry, and as long-term carbon storage in soil, but ecological effects in the soil-plant system are not sufficiently known. Therefore, we investigated the influence of different biomass residues and process duration on the molecular composition of hydrochars, and how hydrochar addition to soils affected the germination of spring barley ( L.) seeds. Samples from biomass residues and the corresponding hydrochars were analyzed by pyrolysis-field ionization mass spectrometry (Py-FIMS) and gaseous emissions from the germination experiments with different soil-hydrochar mixtures by gas chromatography/mass spectrometry (GC/MS). The molecular-level characterization of various hydrochars by Py-FIMS clearly showed that the kind of biomass residue influenced the chemical composition of the corresponding hydrochars more strongly than the process duration. In addition to various detected possible toxic substances, two independent mass spectrometric methods (Py-FIMS and GC/MS) indicated long C-chain aliphatic compounds which are typically degraded to the C-unit ethylene that can evoke phytotoxic effects in high concentrations. This showed for the first time possible chemical compounds to explain toxic effects of hydrochars on plant growth. It is concluded that the HTC process did not result in a consistent product with defined chemical composition. Furthermore, possible toxic effects urgently need to be investigated for each individual hydrochar to assess effects on the soil organic matter composition and the soil biota before hydrochar applications as an amendment on agricultural soils.

A new rapid micro-method for the molecular-chemical characterization of rhizodeposits by field-ionization mass spectrometry.

Time-consuming investigation of rhizodeposit composition by leaching, freeze-drying of leachate, and pyrolysis-field ionization mass spectrometry (Py-FIMS) of solid samples was replaced by direct Py-FIMS of a 5 microL liquid rhizodeposit sample which was evaporated overnight in the quartz tube of a mass spectrometer inlet system. Application of this new rapid technique to a set of 14 liquid rhizodeposit samples from maize (Zea mays L.), leached twice with a time lag of 80 min, unequivocally showed the effect of soil texture on the chemical composition of the rhizodeposits. Irrespective of leaching time, a partial least-squares analysis separated the Py-FI mass spectra of the maize rhizodeposits leached from a soil from those leached from a soil + quartz sand-mixture (prepared by addition of 50% w/w quartz sand to the original soil). The signals which had the strongest discrimination power and were significantly enriched in leachates from the soil + quartz sand were assigned to sugars, peptides and polyamines. Mass signals of putrescine and cadaverine, a priori not expected in the rhizodeposits, were indicators of modified root environment and rhizosphere processes in the soil + quartz sand. In conclusion, the new rapid mass spectrometric profiling method is suitable for rhizosphere research because it requires very small sample volumes, is fast and highly sensitive to detect and quantify a wide range of a priori expected and unexpected organic substances.

Nitrogen speciation in fine and coarse clay fractions of a Cryoboroll - new evidence from pyrolysis-mass spectrometry and nitrogen K-edge XANES

Soil clay fractions are usually enriched in nitrogen (N), but the chemical identity of this N is largely unknown. Therefore, we investigated organic N in fine and coarse clay of a clay-rich Cryoboroll by Curie-point pyrolysis-gas chromatography/mass spectrometry (Cp Py-GC/MS), Pyrolysis-field ionization mass spectroscopy (Py-FIMS) and synchrotron-based nitrogen K-edge X-ray absorption near edge structure (N-XANES) spectroscopy. The Cp Py-GC-MS revealed 30 structurally different N-containing compounds, such as substituted pyridines, pyrroles; pyrazines, pyrazoles, imidazoles, quinolines, side-chain N-containing benzenes, and single compounds of substituted benzotriazole, purine and indole. These accounted for about 10% of peak area in the Py-GC chromatograms. The Py-FIMS and N-XANES spectra indicated interlayer-NH4+ and revealed pyridinic and nitrilic N compounds, but disagreed in the proportions of pyrroles. All three complementary methods confirmed to different extents previous wet-chemical data on N-fra...

Chapter 9 – Nitrogen Compounds in Dissolved and Solid Environmental Samples

The chapter describes the state of the art in Nitrogen K-edge X-ray absorption near-edge structure (N-XANES) spectroscopy applied to environmental problems. Technical details of beamline optimization are given as well as advice for sample preparation and spectral evaluation. The thorough overview of reference compounds includes mineral N-compounds, amino acids, amides, nitriles, and a wide range of heterocyclic compounds. We show new evidence of radiation damage on N-XANES spectra of proteinaceous N-reference compounds and soil-related materials, and propose approaches to minimize it. Calculated N-XANES spectra using density functional theory showed excellent agreement with measurements that resolved pyridinic and pyrrolic N in the same molecule. Using environmental samples, we demonstrate that measurements of soil solutions indicate a large contribution of mineral N (NO3−, NH4+). In particle-size fractions and bulk soil samples, differences in the proportions of various N functions may originate from clay-organic matter interactions, rhizosphere processes, and soil management practices. In conclusion, N-XANES is a valuable component in the multimethod approach toward the study of inorganic and organic N in environmental samples.

Solid-phase cadmium speciation in soil using L3-edge XANES spectroscopy with partial least-squares regression

Cadmium (Cd) has a high toxicity and resolving its speciation in soil is challenging but essential for estimating the environmental risk. In this study partial least-square (PLS) regression was tested for its capability to deconvolute Cd L(3)-edge X-ray absorption near-edge structure (XANES) spectra of multi-compound mixtures. For this, a library of Cd reference compound spectra and a spectrum of a soil sample were acquired. A good coefficient of determination (R(2)) of Cd compounds in mixtures was obtained for the PLS model using binary and ternary mixtures of various Cd reference compounds proving the validity of this approach. In order to describe complex systems like soil, multi-compound mixtures of a variety of Cd compounds must be included in the PLS model. The obtained PLS regression model was then applied to a highly Cd-contaminated soil revealing Cd(3)(PO(4))(2) (36.1%), Cd(NO(3))(2)·4H(2)O (24.5%), Cd(OH)(2) (21.7%), CdCO(3) (17.1%) and CdCl(2) (0.4%). These preliminary results proved that PLS regression is a promising approach for a direct determination of Cd speciation in the solid phase of a soil sample.