In my last email, I didn't ask the question clearly. We used BaOH2 to trap the CO2 from soil incubation. With this method, CO2 precipitate to form BaCO3. We want to analyze BaCO3 for d13C and we have an ISOCARB automated carbonate system attached to a VG OPTIMA IRMS. Has anybody analyzed BaCO3 for d13C before? Are there any standards available? How much material do we need to run?