An Improved EA-IRMS Method Using V2O5-Assisted Combustion for Carbon Isotope Analysis of High-Temperature and High-Pressure Metamorphic Graphite.

An improved method was proposed, which addressed the technical challenge of incomplete combustion and conversion of high-temperature, high-pressure metamorphic graphite-a chemically stable material for conventional EA-IRMS method analysis. The method was based on the addition of an efficient oxidant. Using graphite from a Sri Lankan charnockite (G1) and graphite containing pyrite (G2) as test materials, the effects of oxygen injection modes and solid oxidants (CuO and V2O5) on combustion efficiency were evaluated. It was demonstrated that merely increasing oxygen flow rate or duration failed to achieve complete oxidation of the samples, whereas the addition of V2O5 effectively resolved the problem. By optimizing reaction conditions, an optimal analysis method was proposed: mixing the graphite sample with V2O5 at a mass ratio of no less than 1:6 and injecting oxygen at a flow rate of 175 mL/min for 6 s. Under these conditions, both types of refractory graphite samples achieved complete combustion, significantly enhancing carbon conversion efficiency, ensuring the accuracy of δ13C analyses. The method substantially extends the applicability of EA-IRMS technology for isotope analysis of inert geological carbon materials, providing reliable and critical support for research on deep carbon cycling, graphite deposit genesis, and related studies.