Applications of NMR techniques for the identification and structure elucidation of emerging organic and other xenobiotic organic contaminants

Environmentally significant concentrations of organic contaminants (emerging and others) are normally in the range 10–104 ng/L. For their targeted analysis mostly liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) techniques are used. However, an unambiguous structure elucidation of unknown contaminants and transformation products cannot always be achieved by these methods. Nuclear magnetic resonance (NMR) is a powerful tool for the structure elucidation of unknown compounds and provides important information complementary to that of MS. However, NMR can be used only if compound concentrations are at least in the upper ng range. The aim of this chapter is to demonstrate with examples the current possibilities of NMR techniques for the analysis of emerging and other contaminants and of their transformation products in aqueous environmental samples. First basic techniques of sample enrichment and clean-up, tube NMR and hyphenated NMR techniques such as LC-NMR, LC-NMR-(HR)MS, LC-SPE-NMR-(HR)MS are briefly described. Next, papers with the following topics are reviewed: (i) The use of MS and NMR methods for the structure elucidation of unknown metabolites and disinfection by-products which were isolated from laboratory-scale studies. (ii) The direct identification of organic contaminants in aqueous samples from contaminated point sources by MS and/or hyphenated NMR techniques. (iii) The comprehensive NMR characterization of complex technical mixtures that forms a prerequisite for the targeted analysis of their single components in environmental matrices. (iv) Applications of site-specific natural-isotope fractionation nuclear magnetic resonance (SNIF-NMR). The cited literature covers the range from 2005 to 2012 but there is no claim to completeness