Thermally based isotopic speciation of carbon pools in environmental matrices

In the last years several authors applied the thermal speciation techniques to different environmental matrices such as biological material (Boyle et al., 2004; Pallasser et al., 2013) and soils/sediments (Hsieh and Bugna 2008; Bisutti et al. 2007; Leifeld 2007), in order to identify the different carbon pools. The abovementioned methods have been improved by coupling the elemental content with the carbon isotope analysis, which represents a powerful tool for the discrimination of the distinct carbon pools in heterogeneous environmental materials (Lopez-Capel et al. 2006; Manning et al. 2005, 2008). Elemental and isotopic analyses of carbon in environmental matrices usually highlight multiple pools of different composition and 13C/12C (δ13C ‰) isotopic ratio. Interpretation necessarily needs the characterization of the diverse end-members that usually are constituted by inorganic and organic components. In this view, we developed a routine protocol based on coupling of elemental and isotopic analyses that is able to discriminate the inorganic (IC) and organic (OC) contributions to the total carbon (TC) content. The procedure is only based on thermal destabilization of the different carbon pools and has been successfully applied on different environmental matrices (rocks, soils, and biological samples) with a mean C elemental and isotopic recoveries of 99.5 % (SD= 1.3 %) and 0.2‰ (SD=0.2‰), respectively. The thermally based speciation (TBS) leads us to define precise isotopic end -members, which are unaffected by any chemical treatment of the sample, to be used for accurate mass balance calculation that represents a powerful tool to quantify the distinct carbon pools. The paper critically evaluates the method explaining the potentials and the current limits of the proposed analytical protocol.