Premium
Refinement of the Micro‐Distillation Technique for Isotopic Analysis of Geological Samples with pg‐Level Osmium Contents
Author(s) -
Nakanishi Nao,
Yokoyama Tetsuya,
Ishikawa Akira
Publication year - 2019
Publication title -
geostandards and geoanalytical research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.037
H-Index - 73
eISSN - 1751-908X
pISSN - 1639-4488
DOI - 10.1111/ggr.12262
Subject(s) - distillation , osmium , chemistry , isotope dilution , yield (engineering) , analytical chemistry (journal) , vacuum distillation , chromatography , isotope , continuous distillation , mass spectrometry , dilution , materials science , thermodynamics , organic chemistry , metallurgy , ruthenium , catalysis , physics , quantum mechanics
In recent years, the 187 Re– 187 Os isotope system has been increasingly used to study samples containing very small quantities of Os. For such samples, optimisation of measurement procedures is essential to minimise the loss of Os before mass spectrometric measurements. Micro‐distillation is a necessary purification step that is applied after the main Os chemical separation procedure, prior to Os isotope ratio measurements by negative‐thermal ionisation mass spectrometry (N‐ TIMS ). However, unlike the other separation steps, this procedure has not yet been optimised for small samples. In this study, we present a refined micro‐distillation method that achieved higher yields and allowed high‐precision R( 187 Os/ 188 Os) expressed as 187 Os/ 188 Os measurements for small‐sized geological samples that contain only a few pg Os. The Os recovery in the micro‐distillation step was tested by changing the operating conditions including heating time and temperature, and amounts of oxidant and reductant. Recoveries were measured by the isotope dilution ICP ‐ MS method after the addition of 190 Os‐enriched spike solution. We found that the most critical factor controlling the chemical yield of Os during micro‐distillation is the extent of dilution of the reductant ( HB r) by H 2 O evaporated from the oxidant. A refined micro‐distillation method, in which the amount of oxidant solution is reduced from the conventional method, achieved an improved chemical yield of Os (~ 90%). This refined method was applied to the measurement of 187 Os/ 188 Os by N‐ TIMS of varying test portions of the geological reference material BIR ‐1a. The resulting 187 Os/ 188 Os ratios of BIR ‐1a matched the literature data, with propagated uncertainties of 0.2, 1.1 and 11% digested sample quantities containing 150, 10 and 1 pg of Os, respectively.