Headspace solid phase microextraction - GC/C-IRMS for 13CVPDB measurements of mono-aromatic hydrocarbons using EA-IRMS calibration

This work aims at comparing the 13CVPDB of mono-aromatic hydrocarbons benzene, toluene, ethylbenzene and xylene isomers (BTEX) measured by elemental analyser (EA)-isotope ratio mass spectrometer (IRMS) with the 13CVPDB 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 13CVPDB 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 13CVPDB 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 13CVPDB measurements of the BTEX by the hSPME - GC/C-IRMS system. The comparison made between the 13CVPDB measured on the same BTEX compounds by EA-IRMS (with external calibration) and by hSPME - GC/C-IRMS techniques showed good agreement.