Simplifying silver isotope analysis of metallic samples: using silver nitrate precipitation to avoid perilous chloride formation

McCoy-West, Alex J., Davis, Alison M., Wainwright, Ashlea N., and Tomkins, Andrew G. (2024) Simplifying silver isotope analysis of metallic samples: using silver nitrate precipitation to avoid perilous chloride formation. Journal of Analytical Atomic Spectrometry, 39 (3). pp. 780-790.

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Silver (Ag) isotopes have the potential to provide useful insights into a diverse range of geological, environmental, and archaeological processes. This manuscript presents a novel technique that provides a simple, time-efficient, and accurate method for obtaining Ag isotope compositions of metallic gold (Au) samples. Unlike previous methodologies that favoured multiple ion exchange columns to purify and isolate Ag in nitrate form. This technique instead uses a single anion-exchange column, followed by the chemical conversion of Ag from chloride to nitrate form using the widely available reagents, ammonium hydroxide and ascorbic acid. This chemical conversion not only speeds up and simplifies sample processing allowing increased sample throughput, but importantly also significantly reduces the risk of Ag loss (and therefore user-induced isotopic fractionation) while converting the samples into a medium suitable for mass spectrometry. In this study, both pure Ag and native Au samples have been investigated, with Ag isotope compositions given relative the NIST SRM978a Ag standard. The long-term reproducibility of the in-house Sigma MON Ag solution was ϵ109Ag = 1.32 ± 0.31 (2 s.d.; n = 34), which is comparable to the precision achievable for unprocessed high-purity Ag samples with replicate analyses generating an average precision of ϵ109Ag = ± 0.25 (2 s.d.; n = 5). Comparable levels of precision were also achieved for natural Au samples, indicating that this methodology has no resolvable effect on the precision of the Ag isotope measurements. The natural Au standard CEZAg was used to test the external reproducibility of the chemical separation and conversion technique, yielding an average value of ϵ109Ag = 0.34 ± 0.13 (2 s.d.; n = 6), which is within analytical uncertainty of the previous determinations, demonstrating the accuracy of the new methodology. Furthermore, analysis of natural Au gold nuggets from the Fosterville Au Mine using the chemical conversion process described herein and a previously published multiple column method at a different institution produced consistent Ag isotope compositions, confirming the accuracy of the measurements generated using this method.

Item ID: 82047
Item Type: Article (Research - C1)
ISSN: 1364-5544
Copyright Information: © The Royal Society of Chemistry 2024
Funders: Australian Research Council (ARC)
Projects and Grants: ARC FL160100168, ARC DE210101395, ARC LP015100717
Date Deposited: 21 Mar 2024 04:17
FoR Codes: 37 EARTH SCIENCES > 3703 Geochemistry > 370303 Isotope geochemistry @ 80%
37 EARTH SCIENCES > 3705 Geology > 370508 Resource geoscience @ 20%
SEO Codes: 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280107 Expanding knowledge in the earth sciences @ 80%
25 MINERAL RESOURCES (EXCL. ENERGY RESOURCES) > 2503 Mineral exploration > 250305 Precious (noble) metal ore exploration @ 20%
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