The application of H-1 HR-MAS NMR spectroscopy for the study of structuresand associations of organic components at the solid - Aqueous interface ofa whole soil

High resolution-magic angle spinning nuclear magnetic resonance MR-MAS NMR) allows the application of solution state NMR experiments to samples that a re not fully soluble and contain solids. Only the species in contact with t he solvent system employed become NMR observable. In this study utilizing D 2O as the solvent system we show it is possible to examine the structures a t the solid-aqueous interface of a whole soil. Combining one- and two-dimen sional HR-MAS NMR allowed, for the first time, the identification of fatty acids, aliphatic esters, and ethers/ alcohols as prominent species at the s olid-aqueous interface of the soil with signals from sugars and amino acids also apparent. Few, if any signals from aromatic protons were observed whe n the soil was swollen in aqueous media, although these signals are observe d in extracts from the same soil and when the soil is swollen with a more p enetrating solvent (DMSO-d(6)) which is known to disassociate hydrogen bond s. These findings indicate that the soil aromatic moieties are protected in hydrophobic regions which are not water accessible. Furthermore, when the soil was amended with a herbicide (trifluralin), direct observations of int eractions between the protons on a xenobiotic and the surrounding soil matr ix were possible for the first time. HR-MAS promises to be a method that ca n be widely applicable to a range of complex environmental samples without the need for extraction, pretreatment, or purification.