日本地球惑星科学連合2018年大会

講演情報

[JJ] ポスター発表

セッション記号 S (固体地球科学) » S-GC 固体地球化学

[S-GC46] 固体地球化学・惑星化学

2018年5月22日(火) 15:30 〜 17:00 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:下田 玄(産業技術総合研究所地質調査総合センター)、鈴木 勝彦(国立研究開発法人海洋研究開発機構・海底資源研究開発センター)、山下 勝行(岡山大学大学院自然科学研究科、共同)、石川 晃(東京大学大学院総合文化研究科)

[SGC46-P04] MC-ICP-MS (Nu Plasma II)による高精度銀同位体分析法

*福山 繭子1 (1.秋田大学大学院理工学研究科)

キーワード:銀同位体、MC-ICP-MS

Silver isotopic composition has received special attention because of its ability to trace processes in the very early solar system. The Ag isotopic measurements were previously performed by thermal ionization mass spectrometry (TIMS) with the limited precision of ~1-2 per mil. Silver has two isotopes, 107Ag and 109Ag, thus internal correction for the mass fractionation induced by thermal ionization is not possible. The level of the precision obtained with TIMS is not sufficient to examine small differences of silver isotope compositions on terrestrial samples. However, multi-collector inductively-coupled-plasma mass spectrometry (MC-ICP-MS) leads the improvement of analytical precision for Ag isotope analyses to resolve the very small differences in Ag isotope compositions. It has already led to the discovery of Ag isotopic variation in native Ag metal samples from ore deposits which have varied by up to 0.6 %, due to mass dependent stable isotope fractionations during natural chemical processing (Hauri et al., 2000). This indicates that Ag isotopes may be a useful geochemical tracer, i.e., ore deposits and hydrothermal geochemistry studies.
The improved Ag isotope analytical method using MC-ICP-MS (Nu Plasma II) at Akita University is presented, which permits isotopic analyses of small quantities of Ag (10 ng). This technique is suitable for terrestrial materials. The average 107Ag/109Ag = 1.08041 ± 0.00004 (2 S.D., standard deviation of the population) was obtained for the NIST SRM 978a Ag reference material in wet plasma mode. This value is identical within uncertainty to the ratio reported by previous studies (Fig. 1).