Hydropyrolysis as a new tool for radiocarbon pre-treatment and the quantification of black carbon (original) (raw)
A wide selection of thermal, chemical and optical methods have been proposed for the quantification of black carbon (BC) in environmental matrices, and the results to date differ markedly depending upon the method used. A new approach is hydropyrolysis (hypy), where pyrolysis assisted by high hydrogen pressures (150 bar) facilitates the complete reductive removal of labile organic matter, so isolating a highly stable portion of the BC continuum (defined as BChypy). Here, the potential of hypy for the isolation and quantification of BC is evaluated using the 12 reference materials from the International BC Ring Trial, comprising BC-rich samples, BC-containing environmental matrices and BC-free potentially interfering materials. By varying the hypy operating conditions, it is demonstrated that lignocellulosic, humic and other labile organic carbon material (defined as non-BChypy) is fully removed by 550°C, with hydrogasification of the remaining BChypy not commencing until over 575°C....
Rapid communications in mass spectrometry : RCM, 2012
RATIONALEPyrogenic carbon (CP) is an important component of the global carbon budget. Accurate determination of the abundance and stable isotope composition of CP in soils and sediments is crucial for understanding the dynamics of the CP cycle and interpreting records of biomass burning, climate and vegetation change in the past. Here we test hydrogen pyrolysis (hypy) as a new technique potentially capable of eliminating labile organic carbon (CL) from total organic carbon (CT) in a range of matrices in order to enable reliable quantification of both the CP component of CT and the stable carbon isotope composition of CP (δ13CP).Pyrogenic carbon (CP) is an important component of the global carbon budget. Accurate determination of the abundance and stable isotope composition of CP in soils and sediments is crucial for understanding the dynamics of the CP cycle and interpreting records of biomass burning, climate and vegetation change in the past. Here we test hydrogen pyrolysis (hypy) as a new technique potentially capable of eliminating labile organic carbon (CL) from total organic carbon (CT) in a range of matrices in order to enable reliable quantification of both the CP component of CT and the stable carbon isotope composition of CP (δ13CP).METHODSWe mixed CP at a range of concentrations with common CP-free matrices (CL = cellulose, chitin, keratin, decomposed wood, leaf litter, grass and algae) and determined the amount of residual carbon not removed by hydrogen pyrolysis (CR) as a ratio of CT (CR/CT). Mixing CP with a unique δ13C value provided a natural abundance isotope label from which to precisely determine the ratio of CP to residual CL remaining after hypy.We mixed CP at a range of concentrations with common CP-free matrices (CL = cellulose, chitin, keratin, decomposed wood, leaf litter, grass and algae) and determined the amount of residual carbon not removed by hydrogen pyrolysis (CR) as a ratio of CT (CR/CT). Mixing CP with a unique δ13C value provided a natural abundance isotope label from which to precisely determine the ratio of CP to residual CL remaining after hypy.RESULTSAll CP-free matrices contained trace carbon after hypy, indicating that hypy does not remove all the CL. However, there was a strong correlation between CR/CT and CP/CT, viz. CR/CT = 1.02(CP/CT) + 4.0 × 10–3, r2 = 0.99, p <0.001, suggesting that only a small and reasonably constant fraction of CL remains after hypy. Uncertainties associated with the correction for contamination of CR by residual CL are minimal allowing for reliable determinations of both CP and δ13CP in many cases.All CP-free matrices contained trace carbon after hypy, indicating that hypy does not remove all the CL. However, there was a strong correlation between CR/CT and CP/CT, viz. CR/CT = 1.02(CP/CT) + 4.0 × 10–3, r2 = 0.99, p <0.001, suggesting that only a small and reasonably constant fraction of CL remains after hypy. Uncertainties associated with the correction for contamination of CR by residual CL are minimal allowing for reliable determinations of both CP and δ13CP in many cases.CONCLUSIONSHydrogen pyrolysis appears to be a robust technique for estimating CP abundance and δ13CP across a range of materials. Nevertheless, caution is required in interpreting δ13CP values when CP/CT is low, with CP/CT >4% being required for the determination of the δ13CP values within an interpretable error under our experimental conditions. Copyright © 2012 John Wiley & Sons, Ltd.Hydrogen pyrolysis appears to be a robust technique for estimating CP abundance and δ13CP across a range of materials. Nevertheless, caution is required in interpreting δ13CP values when CP/CT is low, with CP/CT >4% being required for the determination of the δ13CP values within an interpretable error under our experimental conditions. Copyright © 2012 John Wiley & Sons, Ltd.