Ishimura Toyoho, Tsunogai Urumu, Nakagawa Fumiko
Earth and Planetary System Science, Faculty of Science, Hokkaido University, Sapporo, Hokkaido, Japan.
Rapid Commun Mass Spectrom. 2008 Jun;22(12):1925-32. doi: 10.1002/rcm.3571.
We determined grain-scale heterogeneities (from 6 to 88 microg) in the stable carbon and oxygen isotopic compositions (delta(13)C and delta(18)O) of the international standard calcite materials (NBS 19, NBS 18, IAEA-CO-1, and IAEA-CO-8) using a continuous-flow isotope ratio mass spectrometry (CF-IRMS) system that realizes a simultaneous determination of the delta(13)C and the delta(18)O values with standard deviations (S.D.) of less than 0.05 per thousand for CO(2) gas. Based on the S.D. of the delta(13)C and delta(18)O values determined for CO(2) gases evolved from the different grains of the same calcite material, we found that NBS 19, IAEA-CO-1, and IEAE-CO-8 were homogeneous for delta(13)C (less than 0.10 per thousand S.D.), and that only NBS 19 was homogeneous for delta(18)O (less than 0.14 per thousand S.D.). On the level of single grains, we found that both IAEA-CO-1 and IAEA-CO-8 were heterogeneous for delta(18)O (1.46 per thousand and 0.76 per thousand S.D., respectively), and that NBS 18 was heterogeneous for both delta(13)C and delta(18)O (0.34 per thousand and 0.54 per thousand S.D., respectively). Closer inspection of NBS 18 grains revealed that the highly deviated isotopic compositions were limited to the colored grains. By excluding such colored grains, we could also obtain the homogeneous delta(13)C and delta(18)O values (less than 0.18 per thousand and less than 0.16 per thousand S.D., respectively) for NBS 18. We conclude that NBS 19, IAEA-CO-1, or pure grains in NBS 18 are suitable to be used as the standard reference material for delta(13)C, and that either NBS 19 or pure grains in NBS 18 are suitable to be used as the reference material for delta(18)O during the grain-scale isotopic analyses of calcite.
我们使用连续流同位素比率质谱（CF - IRMS）系统测定了国际标准方解石材料（NBS 19、NBS 18、IAEA - CO - 1和IAEA - CO - 8）稳定碳和氧同位素组成（δ¹³C和δ¹⁸O）中的粒度异质性（6至88微克），该系统能够同时测定CO₂气体的δ¹³C和δ¹⁸O值，其标准偏差（S.D.）小于0.05‰。基于对同一块方解石材料不同颗粒释放出的CO₂气体所测定的δ¹³C和δ¹⁸O值的标准偏差，我们发现NBS 19、IAEA - CO - 1和IEAE - CO - 8在δ¹³C方面是均匀的（标准偏差小于0.10‰），并且只有NBS 19在δ¹⁸O方面是均匀的（标准偏差小于0.14‰）。在单个颗粒层面，我们发现IAEA - CO - 1和IAEA - CO - 8在δ¹⁸O方面都是异质的（标准偏差分别为1.46‰和0.76‰），并且NBS 18在δ¹³C和δ¹⁸O方面都是异质的（标准偏差分别为0.34‰和0.54‰）。对NBS 18颗粒的进一步检查表明，高度偏离的同位素组成仅限于有色颗粒。通过排除这些有色颗粒，我们也能够获得NBS 18均匀的δ¹³C和δ¹⁸O值（标准偏差分别小于0.18‰和小于0.16‰）。我们得出结论，NBS 19、IAEA - CO - 1或NBS 18中的纯净颗粒适合用作δ¹³C的标准参考材料，并且NBS 19或NBS 18中的纯净颗粒都适合在方解石的粒度同位素分析期间用作δ¹⁸O的参考材料。
