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Measurements of delta B-11 in water by use of a mass spectrometer with accelerator


This study describes the tests carried out to measure the isotopic composition of Boron (B) in water samples by use of the magnetic spectrometer and accelerator of the Center for Isotopic Research on Cultural and Environmental heritage (CIRCE) of Italy. B was extracted from water samples to obtain Boric acid (B(OH)3), which was then analyzed. We quantified the precision of our experimental system and the variability introduced by the chemical extraction measuring chemically untreated and treated pure B(OH)3 samples. We found an instrumental precision around 10‰ (1s), but, by increasing the number of replicates (>30), we obtained a standard deviation of the mean (serr) around 3‰ or lower. We also tested whether the chemical extraction caused isotopic fractionation and found a small fractionation (e = 5 ± 4‰) of treated samples normalized against untreated ones, compatible with zero at 2s. In order to avoid d11B biases, we decided to normalize unknown treated samples with treated standards. Finally, we measured d11B of seawater and groundwater samples to test the analytical method, and obtained values of 30 ± 6‰ and -4 ± 4‰ respectively. We conclude that our experimental system is only suitable when remarkable (>10‰) d11B differences exist among water samples, but cannot be used to measure natural differences (<10‰) unless the total uncertainty is significantly decreased.

Acceptance Date Sep 11, 2017
Publication Date Dec 1, 2017
Journal Nuclear Instruments & Methods In Physics Research Section B: Beam Interactions With Materials And Atoms
Print ISSN 0168-583X
Publisher Elsevier
Pages 109 -114
Keywords Boron isotope ratio, Seawater, Groundwater, Boron concentration
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