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Coupling of thermal analysis with quadrupole mass spectrometry and isotope ratio mass spectrometry for simultaneous determination of evolved gases and their carbon isotopic composition

Lookup NU author(s): Dr Elisa Lopez-Capel, Dr Geoffrey Abbott, Emeritus Professor Mark Thomas, Professor David Manning

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Abstract

By coupling an isotope ratio mass spectrometer (IRMS) and a quadrupole mass spectrometer (QMS) to a thermal analysis system, we have been able to continuously measure delta(13)C and identify the evolved gases during the thermal decomposition of a range of lignocellulosic materials derived from soils and/or plant tissue. Here we describe the application of this approach to characterise wheat straw during fungal degradation by the oyster mushroom Pleurotus ostreatus. For samples of straw collected over 63 days, TG-DSC showed progressively decreasing contributions of cellulose (300-350 degrees C) and lignin (400-450 degrees C) with concomitant increases in the extents of aromatisation and polycondensation (450-500 degrees C). TG-DSC-QMS analysis showed changes with time in the evolution of different C and N species. H2O and CO2 were the dominant evolved gases observed during the combustion of undegraded and fungally decomposed wheat straw. The relative ion intensities of the gas species NO (m/z 30) and CO2 (m/z 44) observed at 350 degrees C increased at 530 degrees C with increasing wheat straw decomposition. This suggests that fungal degradation results in increasing proportions of C and N incorporated within recalcitrant structures. IRMS analysis showed that fungal decomposition of wheat straw involves homogenization of an initially heterogeneous delta(13)C signal with increasing extent of fungal decay. Undegraded wheat straw has two components: cellulosic material with delta(13)C of -23.8% and lignin with delta(13)C of -26.1%. After 9 weeks fungal degradation, delta(13)C values converged to give -21.3 +/- 0.8%. This is consistent with preferential loss during degradation of lignin that is depleted in C-13 compared to cellulose, and accumulation of C-13-rich components within the degraded straw. (C) 2005 Elsevier B.V. All rights reserved.


Publication metadata

Author(s): Lopez-Capel E, Abbott GD, Thomas KM, Manning DAC

Publication type: Article

Publication status: Published

Journal: Journal of Analytical and Applied Pyrolysis

Year: 2006

Volume: 75

Issue: 2

Pages: 82-89

ISSN (print): 0165-2370

ISSN (electronic): 1873-250X

URL: http://dx.doi.org/10.1016/j.jaap.2005.04.004

DOI: 10.1016/j.jaap.2005.04.004


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