Trubač Jakub, Magna Tomáš, Čejková Bohuslava, Vondrovicová Lenka, Rapprich Vladislav
Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Albertov 6, CZ-12843, Prague 2, Czech Republic.
Czech Geological Survey, Klárov 3, CZ-11821, Prague 1, Czech Republic.
Rapid Commun Mass Spectrom. 2019 Aug 30;33(16):1355-1362. doi: 10.1002/rcm.8482.
Applications where stable C and O isotope compositions are useful require routine instrumental techniques with a fast sample throughput which should also produce accurate and precise results. We present a comparison of three different instrumental isotope ratio mass spectrometry (IRMS) approaches (Dual Inlet - DI; Elemental Analyzer - EA; Continuous Flow - CF) to determine the stable isotope composition of carbon in carbonate matrices, with a focus on evaluating the optimum approach for less complex instrumental techniques.
The DI-IRMS method is taken as an absolute method for obtaining accurate and precise C/ C ratios with internal errors usually < ±0.01‰ (2SD) and long-term reproducibility better than ±0.03‰ (2SD). The drawbacks of DI-IRMS are that it requires extensive offline sample preparation, rather large sample sizes (commonly >20 mg) and extended analysis times.
EA-IRMS provides rapidity of analysis, relatively non-complex technique optimization and large sample throughput sufficient to distinguish natural trends although the larger internal errors and poorer reproducibility must be considered. The major disadvantage of EA-IRMS lies in a constant offset of the C/ C ratios against DI-IRMS, large internal errors (±0.2‰, 2SD) and the worst reproducibility (±0.3‰, 2SD) of all the explored methods. The results acquired using CF-IRMS are comparable with those obtained by employing DI-IRMS with an external reproducibility better than ±0.2‰ (2SD). Compared with EA-IRMS, however, this technique requires more elaborate sample preparation - more akin to DI-IRMS. None of these two latter techniques can provide C isotope results for coexisting phases such as calcite, dolomite and ankerite unless they are physically separated and analyzed independently.
All methods are appropriate for C/ C determinations with CF-IRMS and EA-IRMS less applicable to high-precision measurements but relevant for studies requiring high sample throughput. Periodical analysis of matrix-matched reference materials during the analytical sequence is warranted for both EA-IRMS and CF-IRMS.
在需要稳定碳和氧同位素组成的应用中，需要具备快速样品通量的常规仪器技术，同时还应产生准确和精确的结果。我们比较了三种不同的仪器同位素比质谱（IRMS）方法（双进样 - DI；元素分析仪 - EA；连续流 - CF），以确定碳酸盐基质中碳的稳定同位素组成，重点是评估较简单仪器技术的最佳方法。
DI - IRMS方法被视为一种绝对方法，用于获得准确和精确的(^{13}C/^{12}C)比值，内部误差通常<±0.01‰（2SD），长期重现性优于±0.03‰（2SD）。DI - IRMS的缺点是需要大量的离线样品制备、相当大的样品量（通常>20mg）和较长的分析时间。
EA - IRMS提供了分析速度快、技术优化相对不复杂以及样品通量足以区分自然趋势的优点，尽管必须考虑较大的内部误差和较差的重现性。EA - IRMS的主要缺点在于(^{13}C/^{12}C)比值相对于DI - IRMS存在恒定偏差、内部误差大（±0.2‰，2SD）以及在所有探索方法中重现性最差（±0.3‰，2SD）。使用CF - IRMS获得的结果与采用DI - IRMS获得的结果相当，外部重现性优于±0.2‰（2SD）。然而，与EA - IRMS相比，该技术需要更精细的样品制备——更类似于DI - IRMS。除非方解石、白云石和铁白云石等共存相进行物理分离并独立分析，否则后两种技术都无法提供其碳同位素结果。
所有方法都适用于(^{13}C/^{12}C)测定，CF - IRMS和EA - IRMS不太适用于高精度测量，但适用于需要高样品通量的研究。对于EA - IRMS和CF - IRMS，在分析过程中定期分析基质匹配的参考物质是必要的。
