Determination of Re, Os, Ir, Ru, Pt, Pd Mass Fractions and ¹⁸⁷Os/¹⁸⁸Os Ratios of Organic‐Rich Geological Reference Materials

Abstract

At present, reported data for Re‐PGE mass fractions (in particular) and 187Os/188Os isotope ratios of organic‐rich reference materials (RMs) are rare, hampering the comparison of data quality between different laboratories. In this study, we measured the Re‐PGE (Os, Ir, Ru, Pt and Pd) mass fractions, as well as 187Os/188Os isotope ratios of five shale RMs, including USGS SGR‐1b (oil shale), SBC‐1 (marine shale), SCo‐2 (silty marine shale), ShTX‐1 (calcareous organic‐rich shale) and ShCX‐1 (calcareous shale), and one oil RM, NIST RM 8505. The results show that the five shale RMs have similar upper continental crust‐normalised PGE‐Re patterns and are generally homogeneous in Re‐PGE mass fractions and 187Os/188Os isotope ratios at test portions of 0.2–0.5 g, and thus can be used as matrix‐matched RMs for Re‐Os and PGE of shale samples. The oil RM NIST 8505 and its asphaltene separates are also roughly homogeneous in Re‐PGE mass fractions and 187Os/188Os isotope ratios at test portions of 0.1–0.3 g and can potentially be used as an oil RM for Re‐Os and PGE.

An improved chromatographic method for separation of Re and PGE mass fractions in organic-rich geological samples

“…Mixed 185 Re-190 Os and 191 Ir-99 Ru-194 Pt-105 Pd spike solutions calibrated as described in Wang et al were used. 18 Cation exchange columns were prepared using 30 ml Bio-Rad Econo-Pac columns (i.d. = 1.5 cm), packed with 20 ml AG 50W-X8 (200-400 mesh) resin.…”

“…Previous studies demonstrated that this RM is relatively homogenous in Re-Os-PGE mass fractions, 187 Os/ 188 Os and 187 Re/ 188 Os isotope ratios. 18,26 NIST RM 8505 is a Venezuelan crude oil certied for its vanadium concentration. Previous studies have comprehensively investigated its Re and Os mass fractions and Os isotopic compositions in whole oil, asphaltene separates (ASPH, n-alkane insoluble) and maltene separates (n-alkane soluble).…”

“…The results demonstrated that NIST 8505 has relatively homogenous Re and Os concentrations and Os isotopic composition, such that it can be used as a matrix-matched RM for crude oil samples. 18,19,27,28 We separated its asphaltene precipitates aer n-heptane extraction of maltene for Re-Os and PGE analysis, with the detailed procedure described in Wang et al 18…”

“…Aer sample digestion, we followed the same procedure described in Wang et al to separate and purify Os. 18,29,30 2.2.2 Chemical separation and purication of Re and PGE. The remaining solution aer Os extraction was evaporated to dryness, and the residue was dissolved in 5 ml of 6 mol l −1 HCl at 150 °C overnight, and the solution was dried again.…”

“…This is mainly because only trace levels of these elements are contained in ORGS (generally in the range of ng g −1 -pg g −1 ). 1,[15][16][17][18][19][20] It is highly necessary to isolate the Re-PGE with high purity from ORGS with high recovery and low procedural blanks for precise mass fraction determinations.…”