Nitrogen K-edge XANES - an overview of reference compounds used to identify `unknown' organic nitrogen in environmental samples

• Published in: Journal of synchrotron radiation 2007-11, Vol.14 (6), p.500-511
• Main Authors: Leinweber, Peter, Kruse, Jens, Walley, Fran L., Gillespie, Adam, Eckhardt, Kai-Uwe, Blyth, Robert I. R., Regier, Tom
• Format: Article
• Language: English
• Subjects: Amino Acids - analysis; Environmental Pollutants - analysis; heterocycles; Heterocyclic Compounds, 4 or More Rings - analysis; NEXAFS; Nitrogen - analysis; Nitrogen Compounds - analysis; radiation damage; soft X-ray spectroscopy; Soil - analysis; soil nitrogen; Spectrum Analysis; X-Rays
• ISSN: 1600-5775; 0909-0495; 1600-5775
• DOI: 10.1107/S0909049507042513

The chemical nature of soil organic nitrogen (N) is still poorly understood and one‐third to one‐half of it is typically classified as `unknown N'. Nitrogen K‐edge XANES spectroscopy has been used to develop a systematic overview on spectral features of all major N functions in soil and environmental samples. The absolute calibration of the photon energy was completed using the 1s→π* transitions of pure gas‐phase N2. On this basis a library of spectral features is provided for mineral N, nitro N, amino acids, peptides, and substituted pyrroles, pyridines, imidazoles, pyrazoles, pyrazines, pyrimidines and purine bases. Although N XANES was previously considered `non‐destructive', effects of radiation damage were shown for two compound classes and an approach was proposed to minimize it. This new evidence is integrated into a proposal for the evaluation spectra from environmental samples with unknown composition. Thus a basis is laid to develop N K‐edge XANES as a complementary standard research method to study the molecular composition and ecological functions of `unknown N' in soil and the environment.