Headspace solid phase microextraction - GC/C-IRMS for δ~(13)C_(VPDB) measurements of mono-aromatic hydrocarbons using EA-IRMS calibration

摘要

This work aims at comparing the δ~(13)C_(VPDB) of mono-aromatic hydrocarbons benzene, toluene, ethylben-zene and xylene isomers (BTEX) measured by elemental analyser (EA)-isotope ratio mass spectrometer (IRMS) with the δ~(13)C_(VPDB) 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: NBS 19 and L-SVEC for establishing the δ~(13)C_(VPDB) 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 Confloll interface device could not be avoided. As the selected hydrocarbons: BTEX could not be analysed by EA-IRMS without helium dilution, their δ~(13)C_(VPDB) must be corrected from this observed bias using an external calibration. The CO_2 gas calibrated using EA-IRMS without helium dilution, was used as an in-house reference for the δ~(13)C_(VPDB) measurements of the BTEX by the hSPME - GC/C-IRMS system. The comparison made between the δ~(13)C_(VPDB) measured on the same BTEX compounds by EA-IRMS (with external calibration) and by hSPME - GC/C-IRMS techniques showed good agreement.