Department of Climate Geochemistry, Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, Mainz, 55128, Germany.
Department of Earth and Planetary Sciences, University California Davis, Davis, CA, 95616, USA.
Rapid Commun Mass Spectrom. 2020 Oct 15;34(19):e8878. doi: 10.1002/rcm.8878.
Oxygen (δ O) and carbon (δ C) isotope analysis of foraminifera and other CaCO samples has been a key technique for paleoceanographical and paleoclimatological research for more than 60 years. There is ongoing demand for the analysis of ever smaller CaCO samples, driven, for example, by the desire to analyse single specimen planktic foraminifera, or small samples of tooth enamel.
We present a continuous-flow mass spectrometric technique that uses cryo-focusing of sample CO to analyse CaCO samples in a weight range between 10 and 3 μg. These are considerably lower sample weights than achievable on most currently available standard instrumentation. The technique is automated, so that sample throughput lies at >60 samples per day. The method involves an on-line vial-flushing routine designed to remove machine drift due to blank CO build-up in the sample vials.
In a series of experiments the effect of blank CO build-up is quantified, and outgassing from the chlorobutyl septa identified as the source. An improved flushing routine together with the use of a cryo-focusing step in the analysis is demonstrated to provide the analytical stability and sensitivity to analyse CaCO samples in a weight range between 10 and 3 μg at ≤0.1‰ precision (1σ) for both δ O and δ C values. The technique yields similarly precise results for the analysis of the structural carbonate fraction of small tooth enamel samples.
This study demonstrates that high-precision oxygen and carbon isotope analysis is possible on CaCO samples smaller than 5 μg by use of a continuous-flow isotope technique. Of key importance are (1) the application of a cold trap that drastically reduces sample gas loss, and (2) a modified flushing regime that eliminates increasing background CO build-up in sample vials during longer automated sample runs.
有孔虫和其他碳酸钙样品的氧（δ O）和碳（δ C）同位素分析已经成为古海洋学和古气候学研究 60 多年的关键技术。由于分析单个浮游有孔虫标本或少量牙釉质样本的需求，对分析更小碳酸钙样品的需求一直在持续增长。
我们提出了一种连续流动质谱技术，该技术使用样品 CO 的低温聚焦来分析重量在 10 至 3μg 之间的 CaCO 样品。这些样品重量明显低于大多数现有标准仪器所能达到的重量。该技术是自动化的，因此每天的样品吞吐量超过 60 个。该方法涉及一种在线小瓶冲洗程序，旨在消除由于空白 CO 在样品小瓶中积聚而导致的机器漂移。
在一系列实验中，定量了空白 CO 积聚的影响，并确定氯丁基隔垫是 CO 逸出的来源。改进的冲洗程序以及在分析中使用低温聚焦步骤，被证明可以提供分析稳定性和灵敏度，从而在重量范围为 10 至 3μg 时，以≤0.1‰的精度（1σ）分析δ O 和 δ C 值。该技术还可用于分析小牙釉质样本的结构碳酸盐部分，得到类似的精确结果。
本研究表明，通过使用连续流动同位素技术，对重量小于 5μg 的 CaCO 样品进行高精度的氧和碳同位素分析是可行的。关键因素有 1）应用冷阱可大大减少样品气体损失，以及 2）修改冲洗程序，可消除在较长时间的自动样品运行过程中样品小瓶中背景 CO 不断增加的问题。
