Structural domains in peat as revealed by physical fractionation, sequential chemolysis and N-15 and C-13 CPMAS NMR spectroscopy

摘要

The distribution patterns of different C and N forms in peat seen using solid state 13 C and N-15 NMR spectroscopy were studied after applying a series of physical and chemical treatments. The material analysed includes four series of peat subfractions obtained by: (i) wet sieving, (ii) extraction with solvents specific for removing lipid or humic substances, (iii) mild degradation treatments yielding non-degraded residues (BF3-MeOH transesterification, HI degradation, HCl hydrolysis) and (iv) thermal treatment. in particular the sample series (i) would inform on the influence of particle size in the quantitative speciation of C and N forms in the whole peat material, whereas series (ii) and (iii) should give further insight on the C and N distribution patterns upon the influence of classical reactions considered to selectively remove structural moieties of the peat organic matter, such are carbohydrate-derived, ester-linked alkyl and hydrolyzable peptidic structures. The NMR spectra suggested: (i) a lack of heterocyclic N forms in the coarsest peat granulometric fractions, and their highest concentration in fractions less than 100 mu m in size; (ii) the preferential accumulation of heterocyclic N forms in the humic acid fraction isolated with a chelating extractant (Na4P2O7): (iii) the survival of amide N forms after acid hydrolysis indicating that only a portion of the amide N forms were present in hydrolyzable form: (iv) the fact that heating of the peat was the treatment which most significantly increased the heterocyclic N moiety. (c) 2008 Elsevier Ltd. All rights reserved.