Amount-dependent isotopic fractionation during compound-specific isotope analysis.
The performance of a gas chromatography-combustion-isotope ratio mass spectrometry system (GC-C-IRMS) with respect to the dependence of delta(13)C 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 (CO(2), 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 per thousand 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 delta(13)C 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 delta(13)C 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 delta(13)C values. Residual overall amount-dependent isotope-fractionation can thus be corrected mathematically.
Schmitt
Jochen
J
Institute of Soil Science and Soil Geography, University of Bayreuth, D-95440 Bayreuth, Germany. jschmitt@awi-bremerhaven.de
Glaser
Bruno
B
Zech
Wolfgang
W
D000465:Algorithms; D000596:Amino Acids / Q000032:analysis; D000606:Amino Sugars / Q000032:analysis; D002245:Carbon Dioxide / Q000737:chemistry; D002247:Carbon Isotopes / Q000032:analysis*; D008401:Gas Chromatography-Mass Spectrometry; D006586:Hexanes / Q000737:chemistry; D007202:Indicators and Reagents; D008031:Lignin / Q000032:analysis; D016014:Linear Models; D010636:Phenols / Q000032:analysis; D010743:Phospholipids / Q000032:analysis; D012015:Reference Standards; D014050:Toluene / Q000737:chemistry
D000596:Amino Acids; D000606:Amino Sugars; D002247:Carbon Isotopes; D006586:Hexanes; D007202:Indicators and Reagents; D010636:Phenols; D010743:Phospholipids; D002245:Carbon Dioxide; C026385:n-hexane; D014050:Toluene; D008031:Lignin