Meckler A Nele, Ziegler Martin, Millán M Isabel, Breitenbach Sebastian F M, Bernasconi Stefano M
Geological Institute, ETH Zurich, Sonneggstrasse, 5, 8092, Zürich, Switzerland.
Rapid Commun Mass Spectrom. 2014 Aug 15;28(15):1705-15. doi: 10.1002/rcm.6949.
Carbonate clumped isotope thermometry is a powerful new technique increasingly used in many fields in earth science. Recently, it has been shown that clumped isotope measurements can be performed with a Kiel carbonate preparation device and micro-volume analyses, allowing measurements of small (1.5-2 mg) carbonate samples. However, common data correction schemes rely on measurements of gases prepared offline, potentially leading to unrecognized biases in the results.
We propose a new correction scheme for the Kiel device method including: (1) A pressure-sensitive baseline correction (PBL) of the raw beam signals; (2) Transfer of data to the absolute reference frame; (3) Correction for acid fractionation; (4) Correction for average standard offsets; (5) When necessary, correction for Δ47 scale compression based on offsets among standards with different ordering state. The long-term performance of the new scheme was tested with a large set of standard measurements (N = 432) obtained over the course of 15 months.
The PBL correction reliably removes composition-dependent artifacts, which are commonly corrected for with gas measurements, and offsets observed in micro-volume measurements when ion beams are imbalanced. We show that the shape of the PBL can vary strongly and needs to be properly characterized. Combined PBL and standard correction resulted in long-term stability with standard deviations in Δ47 of 0.012-0.016 ‰ for the five standards over the whole period, close to the average error of 0.011 ‰ observed for individual measurements consisting of 10 replicate analyses.
Our correction scheme eliminates the need for routine gas measurements, allowing for equal treatment of samples and standards with the Kiel device setup. While the PBL and standard data obtained over 15 months reveal variable mass spectrometer behavior, they provide a robust means of correction, yielding reproducible results from small carbonate samples in the long term.
碳酸盐团簇同位素测温法是一种强大的新技术，在地球科学的许多领域中越来越多地被使用。最近，研究表明可以使用基尔碳酸盐制备装置和微量分析进行团簇同位素测量，从而能够测量小至（1.5 - 2毫克）的碳酸盐样品。然而，常见的数据校正方案依赖于离线制备气体的测量，这可能导致结果中存在未被识别的偏差。
我们针对基尔装置法提出了一种新的校正方案，包括：（1）对原始束信号进行压敏基线校正（PBL）；（2）将数据转换到绝对参考系；（3）校正酸分馏；（4）校正平均标准偏差；（5）必要时，基于不同有序状态标准之间的偏差对Δ47尺度压缩进行校正。通过在15个月内获得的大量标准测量值（N = 432）对新方案的长期性能进行了测试。
PBL校正可靠地消除了通常通过气体测量校正的成分依赖性伪影，以及离子束不平衡时在微量测量中观察到的偏差。我们表明PBL的形状可能会有很大变化，需要进行适当表征。PBL和标准校正相结合，在整个期间内，五个标准的Δ47标准偏差为0.012 - 0.016‰，实现了长期稳定性，接近由10次重复分析组成的单个测量中观察到的平均误差0.011‰。
我们的校正方案无需进行常规气体测量，允许使用基尔装置设置对样品和标准进行同等处理。虽然在15个月内获得的PBL和标准数据揭示了质谱仪行为的变化，但它们提供了一种强大的校正方法，从长期来看，能从小碳酸盐样品中产生可重复的结果。
