Quality and comparability of measurement of potentially toxic elements in urban soils by a group of European laboratories

A study has been conducted to assess the quality and comparability of measurement of aqua-regia-soluble cadmium, chromium, copper, iron, manganese, nickel, lead, and zinc in urban soils within a small cohort of European research laboratories specializing in soil science or environmental analytical chemistry. An initial survey indicated that highly variable levels of analytical quality control (e.g. use of certified reference materials) were routinely implemented in participant laboratories. When a set of soil samples—differing in metal contents and in characteristics such as pH and organic-matter content—were exchanged and analysed, approximately 20% of results differed from target values by more than 25%. A principal-component analysis was applied to data for chromium, copper, nickel, lead, and zinc, and proved successful in assessing overall laboratory performance. The study indicates that greater prominence needs to be given to quality assurance and control if comparable data are to be generated in international, collaborative research projects.     

Sulfur 1s near-edge x-ray absorption fine structure (NEXAFS) of thiol and thioether compounds

The speciation and quantification of sulfur species based on sulfur K-edge x-ray absorption spectroscopy is of wide interest, particularly for biological and petroleum science. These tasks require a firm understanding of the sulfur 1s near-edge x-ray absorption fine structure (NEXAFS) spectra of relevant species. To this end, we have examined the gas phase sulfur 1s NEXAFS spectra of a group of simple thiol and thioether compounds. These high-resolution gas phase spectra are free of solid-state broadening, charging, and saturation effects common in the NEXAFS spectra of solids. These experimental data have been further analyzed with the aid of improved virtual orbital Hartree-Fock ab initio calculations. The experimental sulfur 1s NEXAFS spectra show fine features predicted by calculation, and the combination of experiment and calculation has been used to improve assignment of spectroscopic features relevant for the speciation and quantification of the sulfur compounds.     

Substituent effects in the iron 2p and carbon 1s edge near-edge X-ray absorption fine structure (NEXAFS) spectroscopy of ferrocene compounds

The iron 2p and carbon 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of substituted ferrocene compounds (Fe(Cp-(CH3)5)2, Fe(Cp)(Cp-COOH), Fe(Cp-COOH)2, and Fe(Cp-COCH3)2) are reported and are interpreted with the aid of extended Hückel molecular orbital (EHMO) theory and density functional theory (DFT). Significant substituent effects are observed in both the Fe 2p and C 1s NEXAFS spectra. These effects can be related to the electron donating/withdrawing properties of the cyclopentadienyl ligands and their substituents as well as the presence of pi* conjugation between the cyclopentadienyl ligand and unsaturated substituents.     

Towards a detailed understanding of the NEXAFS spectra of bulk polyethylene copolymers and related alkanes

High energy resolution C 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of ethylene-1-alkene copolymers with systematic variations in comonomer content and thus systematic changes in branch length, branching ratio, and degree of crystallinity are presented. Spectral changes of the σ^*_C–H/Rydberg and σ^*_C–C features in these ideal model systems provide unambiguous experimental evidence for intermolecular interactions with profound effects on the spectral intensity, but only very small energy shifts. Ab initio calculations reproduce the experimental results in detail. The intermolecular interaction observed suggests that interpretation of NEXAFS spectra based on calculations of isolated molecules can be insufficient even in relatively weakly interacting macromolecules.