Characterisation of black carbon-rich samples by 13C solid-state nuclear magnetic resonance
- 220 Downloads
There are difficulties in quantifying and characterising the organic matter (OM) in soils that contain significant amounts of partially oxidised char or charcoal materials. The anthropogenic black carbon (BC), such as that found in the Terra Preta de Índio soils of the Amazon region, is a good example of the OM that is difficult to analyse in such soils. 13C direct polarisation/magic angle spinning (DP/MAS) at high MAS frequency, 1H-13C cross polarisation (CP)/MAS with total suppression of spinning sidebands (TOSS), and chemical shift anisotropy (CSA) filter nuclear magnetic resonance techniques have been applied successfully for quantifying the different components of OM. However, because pyrogenic materials present strong local magnetic susceptibility heterogeneities, the use of CSA-filter and TOSS make the pulse sequences very sensitive to imperfections in the π pulses. In this study, the DP/MAS pulse sequence was replaced by a CP with a radio frequency ramp—variable amplitude CP (VACP)—VACP/MAS pulse sequence, and composite π pulses were used in the CSA-filter and TOSS pulse sequences. In that way, the component functionalities in a humic acid from a BC soil were successfully determined. The spectrometer time needed was greatly decreased by employing this VACP/MAS technique. This development provides an accurate method for characterising BC-rich samples from different origins.
KeywordsHumic Acid Black Carbon Magic Angle Spin Chemical Shift Anisotropy International Humic Substance Society
The authors acknowledge support from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)—Brazil, Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)—Brazil, Empresa Brasileira de Pesquisa Agropecuária (Embrapa)—Brazil, and Science Foundation Ireland, and Dr. Vinicius M. Benites (Embrapa Solos) and Dr. Tony J.F. Cunha (Embrapa Semi-Árido) for providing HA samples. The experiments comply with the current Brazilian laws.
- Fitzpatrick SW (1990) Manufacture of furfural and levulinic acid by acid degradation of lignocellulosic. World patent 8910362 to Biofine IncorporatedGoogle Scholar
- Ponomarenko EV, Anderson DW (2001) Importance of charred organic matter in black chernozem soils of Saskatchewan. Can J Soil Sci 81:285–297Google Scholar
- Raleigh DP, Kolbert AC, Griffin RG (1990) The effect of experimental imperfections on TOSS spectra. J Magn Reson 89:1–9Google Scholar