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珊瑚的B同位素组成是海水pH值记录的良好替代指标。对传统的高精度的B同位素组成分析的方法正离子热电离质谱(PTIMS)和负离子热电离质谱(NTIMS)方法进行了对比研究。结果显示,NTIMS分析方法具有极高的灵敏度,可以分析微小样品量,但由于其分馏较明显,并且我们的实验结果表明前人建议的使用O同位素进行分馏校正的方法仅在某些特定情况下适用,而对大多数的测定缺乏有效分馏校正,同时有机质或者激发剂带来的CNO-干扰难以完全排除,因此NTIMS的结果重现性稍差,δ11B外部精度约为±1.0‰(2σ)左右。PTIMS则分馏不明显,Cs2CNO+干扰可以有效监控并排除,可以获得很好的结果:δ11B内部精度和外部精度均优于±0.2‰(2σ),可以满足高精度pH值重建的要求。然而PTIMS方法的灵敏度低,难以对微小样品量进行分析。因此PTIMS和NTIMS方法是相互补充的,相互无法完全取代。
B isotope composition of coral is a good surrogate for seawater pH recording. A comparative study was made on the traditional high-precision B isotopic composition analysis methods of positive ion thermal ionization mass spectrometry (PTIMS) and negative ion thermal ionization mass spectrometry (NTIMS). The results show that the NTIMS method has a very high sensitivity and can analyze the small sample size. However, due to its obvious fractionation, and our experimental results show that the previously proposed method of fractional correction using the O isotope is only possible in certain cases Applicable, and most of the determination of the lack of effective fractionation correction, and CNO-interference caused by organic matter or activator is difficult to completely exclude, so the results of NTIMS reproducibility is slightly worse, δ11B external accuracy of about ± 1.0 ‰ (2σ) around . PTIMS is not obvious fractional distillation, Cs2CNO + interference can be effectively monitored and excluded, you can get good results: δ11B internal accuracy and external accuracy are better than ± 0.2 ‰ (2σ), to meet the requirements of high-precision pH reconstruction. However, the sensitivity of the PTIMS method is so low that it is difficult to analyze the small sample size. Therefore, the PTIMS and NTIMS methods complement each other and can not completely replace each other.