Headspace solid phase microextraction – GC/C-IRMS for δ13CVPDB measurements of mono-aromatic hydrocarbons using EA-IRMS calibration
This work aims at comparing the δ13CVPDB of mono-aromatic hydrocarbons benzene, toluene, ethylbenzene and xylene isomers (BTEX) measured by elemental analyser (EA)-isotope ratio mass spectrometer (IRMS) with the δ13CVPDB measured on the same compounds by headspace solid phase microextraction – GC/C-IRMS (hSPME – GC/C-IRMS) with the final goal of using these compounds as internal standards on the latter system. The EA-IRMS measurements were done using calcium and lithium carbonate isotopic reference materials: NBS19 and L-SVEC for establishing the δ13CVPDB scale. The EA-IRMS measurements with helium dilution of a set of five reference materials (USGS40, USGS41, IAEA-CH-6, IAEA-CH-3 and IAEA-601) show systematic bias of 1‰ relative to their assigned values. This bias due to the dilution mechanism in the used ConfloII interface device could not be avoided. As the selected hydrocarbons: BTEX could not be analysed by EA-IRMS without helium dilution, their δ13CVPDB must be corrected from this observed bias using an external calibration. The CO2 gas calibrated using EA-IRMS without helium dilution, was used as an in-house reference for the δ13CVPDB measurements of the BTEX by the hSPME – GC/C-IRMS system. The comparison made between the δ13CVPDB measured on the same BTEX compounds by EA-IRMS (with external calibration) and by hSPME – GC/C-IRMS techniques showed good agreement.
Inter-laboratory comparison of elemental analysis and gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS). Part I: delta13C measurements of selected compounds for the development of an isotopic Grob-test.
This study was directed towards investigating suitable compounds to be used as stable isotope reference materials for gas chromatography combustion isotope ratio mass spectrometry (GC-C-IRMS) calibration. Several compounds were selected from those used in the 'Grob-test' mixture. Oxygen- and nitrogen-containing substances were added to these compounds to allow the mixture to be used as a possible multi-isotopic calibration tool for 2H/1H, 13C/12C, 15N/14N and 18O/16O ratio determinations. In this paper we present the results of delta13C measurements performed by the consortium of the five laboratories taking part in this inter-calibration exercise. All the compounds were individually assessed for homogeneity, short-term stability and long-term stability by means of EA-IRMS, as required by the bureau communitaire de reference (BCR) Guide for Production of Certified Reference Materials. The results were compared then with the GC-C-IRMS measurements using both polar and non-polar columns, and the final mixture of selected compounds underwent a further certification exercise assessing limits of accuracy and reproducibility under specified GC-C-IRMS conditions.
Isotope ratio mass spectrometric method for the on-line determination of oxygen-18 in organic matter.
A method for the on-line determination of oxygen-18, at a naturally occurring level, in organic material is presented. After pyrolysis of the samples to form carbon monoxide, which is performed at 1300 degrees C in a vitreous carbon tube, the pyrolysis products are transported by a stream of helium gas. Using an open split, a small part of the effluent is transferred to the ion source of an isotope ratio mass spectrometer. The ratio is obtained from a measurement of the ion current intensities at m/z 30 and 28 (12C18O and 12C16O). The method was tested with the secondary water standard GISP (Greenland Ice Sheet Precipitation) and the carbonate standard NBS 19. The values obtained were -24.8/1000 and 27.3/1000 vs. VSMOW (Vienna Standard Mean Ocean Water) (LAEA reference values are -24.8/1000 and 28.7/1000 vs. VSMOW). The potential of the method was demonstrated by measuring the 18O content of samples of beet and cane sucrose and also samples of vanillin extracted from vanilla pods or of synthetic origin.