Organic matter removal for continuous flow isotope ratio mass spectrometry analysis of carbon and oxygen isotope compositions of calcite or dolomite in organic‐rich samples

δ13C and δ18O values of carbonate in organic-rich samples such as soils, biofilms, lake sediments have been scarcely used so far paleo-environmental, biomineralization, or diagenetic studies because organic matter high proportions is suspected to alter isotope analysis. Yet, with the improvement analytical capabilities particular use CF-IRMS, this may not be an issue anymore. To evaluate this, calcite dolomite mixed various yeast (used here a model for immature matter) were measured. The results indicate that measurements by CF-IRMS require removal only when its weight proportion exceeds carbonates. Yeast generated unidentified molecule during phosphoric acid digestion at 25°C (none 80°C), which shifted higher than 50%. It also CO2, but noticeable shift 80°C 25°C) 75%. Three methods tested: well-established NaOCl H2O2 wet treatments well low temperature plasma ashing (LTA) seldom examined. LTA removed shifts, although imperfectly 95%, without dissolution. efficiently shifts all cases dissolved part dolomite. treatment caused severe dissolution while worsening should thus avoided.