Carbon Isotope Analysis for Inorganic Samples by a Continuous Flow Mass Spectrometer

Abstract

We measured carbon abundances and isotopic ratios of inorganic carbon (natural graphite, fullerene, shock-produced diamond) and calcite of sedimentary rocks using ANCA-SL (Automated Nitrogen Carbon Analysis for Solids and Liquids, PDZ Europa Ltd.), which was developed for the routine analyses for the stable isotope study of metabolic cycles. The main problem for the use of this equipment to the inorganic samples is whether the sample is fully combusted or not. We found that graphite was not fully combusted although fullerene and fine diamond were completely combusted. It is likely that the incomplete combustion of the graphite is due to their large grain size used in this study. We also found that there is a variation of isotopic ratios in samples with different weights. The usual precision of δ13C was <0.3‰, but we could reach the precision of <0.1‰ when we used the similar weights for the samples and the standard. The carbon isotopic ratios in calcite from sedimentary rocks have been also measured. The samples were from the mass extinction boundaries, but there was no systematic variation of carbon isotopic ratios across the boundaries.