Coupling NMR to NOM

Abstract

This work itemizes and critically assesses several 1D and multi-dimensional nuclear magnetic resonance (NMR) techniques, in both the liquid (solvent suppression, APT, DEPT, INEPT, COSY, TOCSY, HSQC, HMQC, HMBC, NOESY, ROESY and others) and solid states (DP, SACP, RAMP-CP, CP-TOSS, MQ-DEPT, 2D 1H-13C HETCOR and others), which are relevant to the characterization of natural organic matter (NOM). The pros and cons of many of the discussed techniques are compared in an effort to provide guidance to the most beneficial utilization of these NMR instrumental techniques for researchers interested in gaining insight into various aspects of NOM.

Studies of the Compositions of Humic Acids from Amazonian Dark Earth Soils

“…Although DP is probably the most quantitative 13 C NMR technique (Cook, 2004;Mao and Schmidt-Rohr, 2004), CP is used routinely because it requires less instrument time (Cook, 2004;Simpson and Hatcher, 2004a;Knicker et al, 2005a). Among the different Cross-Polarisation (CP) semi-quantitative methods (Single-Amplitude with MAS -CP/MAS; CP with total suppression of spinning sidebands -CP/TOSS, and VACP with high MAS -VACP/MAS) VACP with high speed MAS (VACP/MAS) is preferred (Cook, 2004).…”

“…However, based on experiments recently proposed (Novotny et al, in press) and reports in the literature (Cook, 2004;Simpson and Hatcher, 2004a;Knicker et al, 2005a), including the possibility of saturation effects in DP experiments due to very long 13 C T 1 (> 300 s), like that observed for O-alkyl groups by Knicker et al (2005a), we opted to replace the DP experiment by the VACP in order to decrease the experimental time.…”

“…The problem is enhanced when carrying out the CSA filter and TOSS experiments required for the quantification method of Mao and Schmidt-Rohr (2004) because these experiments involve the application of many cascaded π pulses that enhance the effect of the pulse imperfections. To overcome this problem we replaced all the π pulses of the CSA filter-TOSS by the composite π pulses, as suggested by Raleigh et al (1990) and Hagemeyer et al (1991) and recommended by Cook (2004). Details of this procedure are in Novotny et al (2006).…”

Characterization of heterogeneities and domains in aquatic and sedimentary organic matter by 1H spin diffusion: Potential for elucidating the formation mechanisms

“…It influences metal speciation and bioavailability, and transport and fate of organic xenobiotics. Under many circumstances, especially in freshwater systems, aquatic NOM functions as the major buffering system and has serious implications for the acidification of rivers, lakes, and oceans (Hedges et al 2000;Cook 2004). Characterization of organic matter in natural waters and sediments is fundamental to the understanding of its origins, compositions, functions, and cycling.…”

“…Despite the extensive efforts to investigate the structures of organic matter using various techniques for many years, a large fraction of this material is not well characterized (Wakeham et al 1997;Hedges et al 2000;Schmidt et al 2009;Gogou and Repeta 2010;Stephens and Minor 2010), and its formation mechanisms are still unclear. Solid-state nuclear magnetic resonance (NMR) spectroscopy is considered as one of the best techniques for characterizing the structures of aquatic and sedimentary organic matter (Pines et al 1973;Mehring 1983;Botto et al 1987;Preston 1996;Nanny et al 1997;Conte and Piccolo 1999;Hatcher et al 2001;Cook 2004;Conte et al 2004;Abdulla et al 2010). The most frequently used solidstate NMR technique is 13 C cross polarization/magic angle spinning (CP/MAS).…”