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

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.