High‐Precision Measurement of ¹⁸⁷Os/¹⁸⁸Os Isotope Ratios of Nanogram to Picogram Amounts of Os in Geological Samples by N‐TIMS using Faraday Cups Equipped with 10¹³ Ω Amplifiers

Abstract

N(187Os)/N(188Os) ratios of six geological reference materials were measured using static Faraday cups (FCs) with 1013 Ω amplifiers by N‐TIMS. Our results show that the repeatability precision was 2–3‰ (2 RSD, n = 3), when taking ~ 1 g of BHVO‐2 with 76 pg g−1 of Os mass fraction and ~ 2 g of BCR‐2 with 21 pg g−1 of Os mass fraction for each sample, whether measured by FCs or by secondary electron multiplier. The repeatability precision measured by FCs was 1–0.2‰ (2 RSD, n = 3) when taking ~ 1 g of BIR‐2 with 350 pg g−1 of Os mass fraction, ~ 1 g of WGB‐1 with 493 pg g−1 of Os mass fraction or ~ 0.5 g of WPR‐1 with 13.3 ng g−1 of Os mass fraction for each sample, which is much better than those measured by secondary electron multiplier. Instead, when taking ~ 2 g of AGV‐2 with 4 pg g−1 Os mass fraction, the repeatability precision measured by secondary electron multiplier is 3–4‰ (RSD, n = 3), which is better than those measured by FCs. Of the six reference materials analysed, WPR‐1 and BIR‐1a are the most homogeneous with regard to Os isotopic composition (2 RSD of 0.08% and 0.23%, respectively) when test portion masses are 0.5–1 g.

Optimisation of 186Os/188Os Measurements by N‐TIMS Using Amplifiers Equipped with 1013 Ω Resistors

“…Recently, Wang et al . (2019) showed that use of 10 13 Ω amplifiers allows precisions of 2–3‰ to be obtained for 187 Os/ 188 Os measurement results of several tens of picograms of Os, demonstrating that these detectors equal or exceed the performance of secondary electron multipliers for these sample sizes. For 186 Os/ 188 Os measurement results, precision better than a few hundred ppm are often required to obtain geologically useful information.…”

Atomic spectrometry update: review of advances in atomic spectrometry and related techniques

“…Os isotope ratios in geological reference materials were determined using MC-ICP-MS by Wang et al 126 They compared 10 13 Ω amplifiers and secondary electron multipliers for measuring the 187 Os : 188 Os ratio. For samples with >80 pg Os, the Faraday collectors gave the best precision, but for <36 pg the electron multiplier was superior.…”

High-precision apatiteδ37Cl measurement by SIMS with a 1012Ω amplifier Faraday cup

“…In the last decade, development on FC preamplifier boards equipped with a 10 12 Ω resistor (and even a 10 13 Ω resistor for thermal ionisation mass spectrometry (TIMS) instrument) allows the reduction of JN noise contribution, and thereby extends the lower-range use of FC detectors. 45,47–50 The adoption of 10 12 Ω amplifier boards for large radius ion microprobes was first performed on SHRIMP instruments, 46 and more recently on CAMECA instruments. 44,51…”