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

中文翻译：

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有机物去除用于连续流动同位素比质谱分析富含有机物样品中方解石或白云石的碳和氧同位素组成

迄今为止，土壤、生物膜和湖泊沉积物等富含有机物的样品中碳酸盐的δ ¹³ C 和 δ ¹⁸ O 值很少用于古环境、生物矿化或成岩研究，因为高比例的有机质被怀疑会改变碳酸盐同位素分析。然而，随着分析能力的提高，特别是 CF-IRMS 的使用，这可能不再是一个问题。为了评估这一点，测量了以不同比例与酵母混合的方解石或白云石的δ ¹³ C 和δ ¹⁸ O 值（此处用作未成熟有机物的模型）。结果表明，方解石或白云石 δ ¹³ C 和 δ ¹⁸CF-IRMS 的 O 只有当其重量比例超过碳酸盐时才需要去除有机物。酵母在 25°C 的磷酸消化过程中产生了一个不明分子（在 80°C 时没有），这使酵母比例高于 50%的碳酸盐 δ ¹⁸ O 值发生了变化。它还产生了 CO ₂，但 δ ¹³ C 和 δ ¹⁸ O 值仅在 80°C（在 25°C 时没有）和酵母比例高于 75% 时发生显着变化。测试了三种去除有机物的方法：成熟的 NaOCl 和 H ₂ O ₂湿处理以及低温等离子灰化 (LTA) 到目前为止很少被检查。LTA 消除了同位素变化，尽管对于 95% 的酵母比例来说是不完美的，没有碳酸盐溶解。NaOCl 有效地消除了所有情况下的同位素变化，但溶解了部分方解石和白云石。H ₂ O ₂处理引起方解石和白云石的严重溶解，同时使δ ¹³ C 和δ ¹⁸ O 位移恶化，因此应避免。