Understanding the Carbon Isotopic Signature in Complex Environmental Matrices

Elemental and isotopic analyses of carbon in environmental matrices usually integrate multiple sources having distinct concentration (wt%) and 13C/12C isotopic ratio. Interpretation necessarily needs the characterization of the diverse end-members that usually are constituted by carbonate, organic and elemental components. In this view, we developed a routine protocol based on the analytical coupling of elementary and isotopic compositions that is able to discriminate the inorganic (TIC) and organic (TOC) contributions to the total carbon (TC) content. The procedure is only based on thermal destabilization of the different carbon species and has been successfully applied on different environmental matrices (rocks, soils, biological samples) with a mean C elemental and isotopic recovery of 99% (SD = 3%) and -0.3‰ (SD = 0.3‰), respectively. The thermal speciation lead us to define precise isotopic end-members whose are unaffected by any chemical treatment of the samples. The approach allows accurate mass balance calculation that represents a powerful tool to quantify the distinct carbon species.