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.