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High‐precision stable isotope analysis of <5 μg CaCO 3 samples by continuous‐flow mass spectrometry
Author(s) -
Vonhof Hubert B.,
Graaf Stefan,
Spero Howard J.,
Schiebel Ralf,
Verdegaal Suzan J.A.,
Metcalfe Brett,
Haug Gerald H.
Publication year - 2020
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.8878
Subject(s) - chemistry , analytical chemistry (journal) , mass spectrometry , stable isotope ratio , isotope ratio mass spectrometry , sample preparation , sample (material) , isotope analysis , instrumentation (computer programming) , chromatography , isotopes of oxygen , physics , quantum mechanics , nuclear chemistry , computer science , operating system , ecology , biology
Rationale Oxygen (δ 18 O) and carbon (δ 13 C) isotope analysis of foraminifera and other CaCO 3 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 3 samples, driven, for example, by the desire to analyse single specimen planktic foraminifera, or small samples of tooth enamel. Methods We present a continuous‐flow mass spectrometric technique that uses cryo‐focusing of sample CO 2 to analyse CaCO 3 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 2 build‐up in the sample vials. Results In a series of experiments the effect of blank CO 2 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 3 samples in a weight range between 10 and 3 μg at ≤0.1‰ precision (1σ) for both δ 18 O and δ 13 C values. The technique yields similarly precise results for the analysis of the structural carbonate fraction of small tooth enamel samples. Conclusions This study demonstrates that high‐precision oxygen and carbon isotope analysis is possible on CaCO 3 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 2 build‐up in sample vials during longer automated sample runs.