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153. Amount-dependent isotopic fractionation during compound-specific isotope analysis

Author

Schmitt, Jochen, Glaser, B., Zech, W., Schmitt, Jochen, Glaser, B., and Zech, W.

Abstract

The performance of a gas chromatography-combustion-isotope ratio mass spectrometry system (GC-C-IRMS) with respect to the dependence of d13C values on the amount of sample is presented. Particular attention is paid to the localization of the amount-dependent isotopic fractionation within the system. Injection experiments with varying amounts of gases (CO2, n-hexane, and toluene) revealed that neither the detector unit nor the combustion reactor, but rather the conditions in the split/splitless injector, contributed to this effect. Although optimization of injector parameters was performed and a reduction of this adverse effect from 3 to 1 was achieved, it was not possible to eliminate isotopic fractionation completely. Consequently, additional injector parameters have to be considered and adjusted to achieve injection conditions free of fractionation. For routine analysis of the compound-specific d13C analysis of different biomarkers in many environmental samples, perfect optimization may not always be reached. Therefore, in order to prevent systematic errors in the measured d13C values due to different sample concentrations, it is suggested that correction for the remaining unknown amount-dependent fractionation can be made by means of co-analyzing standards of varying analyte concentrations and known d13C values. Residual overall amount-dependent isotope-fractionation can thus be corrected mathematically.

Published
2003

157. Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal: A review

Author

Glaser, B., Lehmann, Johannes, Zech, W., Glaser, B., Lehmann, Johannes, and Zech, W.

Abstract

Rapid turnover of organic matter leads to a low efficiency of organic fertilizers applied to increase and sequester C in soils of the humid tropics. Charcoal was reported to be responsible for high soil organic matter contents and soil fertility of anthropogenic soils (Terra Preta) found in central Amazonia. Therefore, we reviewed the available information about the physical and chemical properties of charcoal as affected by different combustion procedures, and the effects of its application in agricultural fields on nutrient retention and crop production. Higher nutrient retention and nutrient availability were found after charcoal additions to soil, related to higher exchange capacity, surface area and direct nutrient additions. Higher charring temperatures generally improved exchange properties and surface area of the charcoal. Additionally, charcoal is relatively recalcitrant and can therefore be used as a long-term sink for atmospheric CO2. Several aspects of a charcoal management system remain unclear, such as the role of microorganisms in oxidizing charcoal surfaces and releasing nutrients and the possibilities to improve charcoal properties during production under field conditions. Several research needs were identified, such as field testing of charcoal production in tropical agroecosystems, the investigation of surface properties of the carbonized materials in the soil environment, and the evaluation of the agronomic and economic effectiveness of soil management with charcoal.

Published
2002

159. Bestimmung substanzspezifischer d13C-Verhältnisse in Ligninphenolen mittels Gaschromatographie-Verbrennungs-Isotopenmassenspektrometrie (GC-C-IRMS)

Author

Schmitt, Jochen, Glaser, B., Zech, W., Schmitt, Jochen, Glaser, B., and Zech, W.

Abstract

Die isotopische Zusammensetzung einer Substanz ist eine Stoffeigenschaft und nicht von der gemessenen Konzentration abhängig. Dennoch fanden wir bei der substanzspezifischen d13C-Analyse von phenolischen Ligninoxidationsprodukten eine Abhängigkeit des d13C-Wertes von der injizierten Substanz-Menge. Durch systematische Untersuchung der einzelnen Gerätekomponenten der Gaschromatographie-Verbrennungs-Isotopenmassenspektrometrie-(GC-C-IRMS)-Konfiguration konnten die Ursachen des mengenabhängigen Isotopen-Signals lokalisiert und mittels geeigneter Parameterwahl weitgehend minimiert werden. Die durchgeführten Experimente ergaben, dass die Isotopenfraktionierung weder am IRMS noch am Oxidationsreaktor stattfindet. Allerdings führen Veränderungen der Injektionsparameter, wie Splitfluss-Rate, Splitless-Zeit und die Spritzenlänge und deren Eintauchtiefe zu deutlich veränderter Abhängigkeit des d13C-Wertes von der injizierten Stoffmenge. Durch Optimierung dieser Parameter konnte die Injektionsmengenabhängigkeit reduziert, jedoch nicht vollständig eliminiert werden, die verbleibende Abhängigkeit konnte durch Anpassung logarithmischer Kalibrierfunktionen rechnerisch korrigiert werden. Angewandt wurde die so optimierte Methode zur substanzspezifischen Bestimmung des d13C-Wertes von phenolischen Ligninoxidationsprodukten als terrestrischen Biomarker höherer Pflanzen innerhalb einer Paläostudie.

Published
2002

160. Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal: A review

Author

Sustainable Agriculture and Natural Resource Management (SANREM) Knowledgebase, Glaser, B., Lehmann, Johannes, Zech, W., Sustainable Agriculture and Natural Resource Management (SANREM) Knowledgebase, Glaser, B., Lehmann, Johannes, and Zech, W.

Abstract

Rapid turnover of organic matter leads to a low efficiency of organic fertilizers applied to increase and sequester C in soils of the humid tropics. Charcoal was reported to be responsible for high soil organic matter contents and soil fertility of anthropogenic soils (Terra Preta) found in central Amazonia. Therefore, we reviewed the available information about the physical and chemical properties of charcoal as affected by different combustion procedures, and the effects of its application in agricultural fields on nutrient retention and crop production. Higher nutrient retention and nutrient availability were found after charcoal additions to soil, related to higher exchange capacity, surface area and direct nutrient additions. Higher charring temperatures generally improved exchange properties and surface area of the charcoal. Additionally, charcoal is relatively recalcitrant and can therefore be used as a long-term sink for atmospheric CO2. Several aspects of a charcoal management system remain unclear, such as the role of microorganisms in oxidizing charcoal surfaces and releasing nutrients and the possibilities to improve charcoal properties during production under field conditions. Several research needs were identified, such as field testing of charcoal production in tropical agroecosystems, the investigation of surface properties of the carbonized materials in the soil environment, and the evaluation of the agronomic and economic effectiveness of soil management with charcoal.

Published
2002

163. Impact of polymorphisms in WFS1 on prediabetic phenotypes in a population-based sample of middle-aged people with normal and abnormal glucose regulation

Author

Sparsø, T., primary, Andersen, G., additional, Albrechtsen, A., additional, Jørgensen, T., additional, Borch-Johnsen, K., additional, Sandbæk, A., additional, Lauritzen, T., additional, Wasson, J., additional, Permutt, M. A., additional, Glaser, B., additional, Madsbad, S., additional, Pedersen, O., additional, and Hansen, T., additional

Published
2008
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187. Hyperinsulinism of Infancy: The Regulated Release of Insulin by KATP Channel--Independent Pathways

Author

Straub, S. G., primary, Cosgrove, K. E., additional, Ammala, C., additional, Shepherd, R. M., additional, O'Brien, R. E., additional, Barnes, P. D., additional, Kuchinski, N.'a., additional, Chapman, J. C., additional, Schaeppi, M., additional, Glaser, B., additional, Lindley, K. J., additional, Sharp, G. W.G., additional, Aynsley-Green, A., additional, and Dunne, M. J., additional

Published
2001
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