A comparison of IRMS and CRDS techniques for isotope analysis of fluid inclusion water

• Published in: Rapid communications in mass spectrometry p. e8837
• Main Authors: de Graaf, Stefan, Vonhof, Hubert B, Weissbach, Therese, Wassenburg, Jasper A, Levy, Elan J, Kluge, Tobias, Haug, Gerald H
• Format: Journal Article
• Language: English
• Published: England 18.05.2020
• ISSN: 1097-0231

On-line oxygen (δ O) and hydrogen (δ H) isotope analysis of fluid inclusion water entrapped in minerals is widely applied in paleo-fluid studies. In the state-of-the-art of fluid inclusion isotope research, however, there is a scarcity of reported inter-technique comparisons to account for possible analytical offsets. Along with improving analytical precisions and sample size limitations, interlaboratory comparisons can lead to a more robust application of fluid inclusion isotope records. Mineral samples - including speleothem, travertine and vein material - were analyzed on two newly set up systems for fluid inclusion isotope analysis to provide an inter-platform comparison. One set-up uses a crusher unit connected on-line to a TC-EA pyrolysis furnace and an isotope ratio mass spectrometry (IRMS) instrument. In the other set-up, a crusher unit is lined up with a cavity ring-down spectroscopy (CRDS) system, and water samples are analyzed on a continuous standard water background to achieve precisions on water injections better than 0.1‰ for δ O values and 0.4‰ for δ H values for amounts down to 0.2 μL. Fluid inclusion isotope analyses on the IRMS set-up have an average 1σ reproducibility of 0.4‰ and 2.0‰ for, respectively, δ O and δ H values. The CRDS set-up has a better 1σ reproducibility (0.3‰ for δ O values and 1.1‰ for δ H values) and also a more rapid sample throughput (< 30 minutes per sample). Fluid inclusion isotope analyses are reproducible at these uncertainties for water amounts down to 0.1 μL on both set-ups. Fluid inclusion isotope data show no systematic offsets between the set-ups. The close match in fluid inclusion isotope results between the two set-ups demonstrates the high accuracy of the presented continuous-flow techniques for fluid inclusion isotope analysis. Ideally, experiments like the one presented here will lead to further interlaboratory comparison efforts and selection of suitable reference materials for fluid inclusion isotopes studies.