High Pressure Asher Digestion and an Isotope Dilution-ICP-MS Method for the Determination of Platinum-Group Element Concentrations in Chromitite Reference Materials CHR-Bkg, GAN Pt-1 and HHH

Abstract

New concentration data for Ru, Rh, Pd, Re, Os, Ir and Pt are presented for three chromitite reference materials. A simple and very effective procedure was applied for the measurements. Samples were spiked with enriched isotopes and digested in a HNO3/HCl (5+2) acid mixture at 300 °C and 125 bar (1.25 × 107 Pa) pressure in a high pressure asher (HPA‐S, Anton Paar). The programme settings were changed as a function of mass (0.5, 1, 2 and 4 g) and time (5 and 15 hours). Complete chromitite dissolutions for three digestions at each setting were monitored using XRD analyses of the amorphous residue after digestion. The osmium concentration was determined by sparging the OsO4 that was formed during digestion into a quadrupole ICP‐MS. After drying and re‐dissolution of the remaining residue, the other PGEs were separated on‐line from their matrix in a simple cation‐exchange column that was coupled to the ICP‐MS. The concentrations were determined through isotope dilution and external calibration (Rh). By using the on‐line separation, we were able to control interference effects (isobaric and molecular), which resulted in highly reproducible data. Replicate measurements of the reference material CHR‐Bkg (SARM CRPG‐CNRS) with sample masses ranging from 0.5 to 4 g showed very small standard deviations compared to the results from the initial collaborative trials and published data (e.g., 3.2% RSD vs. 32% RSD for Ru). Results for platinum showed the largest scatter, which is currently attributed to the small size of the test portion. In addition to CHR‐Bkg, the first results for two chromitite reference materials “platinumore” GAN Pt‐1 and “chromiumore” HHH issued by the Central Geological Laboratory of Mongolia are presented.

Method Development and Optimisation of Sodium Peroxide Sintering for Geological Samples

“…On the other hand, high pressure asher digestions (HPA, 320 °C at 130 bar) have been used effectively for dissolution of chrome spinel (Paliulionyte et al . ). HPA combined with HF was used for complete recovery of HFSE, REEs and refractory phases avoiding time‐consuming PTFE bomb digestion as reported in Cotta and Enzweiler ().…”

“…Microwave-assisted acid digestions of geological samples can also be ineffective for refractory phases and can result in incomplete recoveries of associated trace elements (Totland et al 1992, Sengupta et al 1996, Makishima et al 2002. On the other hand, high pressure asher digestions (HPA, 320°C at 130 bar) have been used effectively for dissolution of chrome spinel (Paliulionyte et al 2006). HPA combined with HF was used for complete recovery of HFSE, REEs and refractory phases avoiding timeconsuming PTFE bomb digestion as reported in Cotta and Enzweiler (2012).…”

Impactites of the elgygytgyn impact crater: U-Pb (SHRIMP) and Re-Os isotope age dating: Peculiarities of their microelement and rare earth element composition and 187Os/188Os Isotopy (Central Chukotka, Russia)

“…The contents of rhenium and osmium were deter mined through the isotope dilution [10] at the Center of Isotopic Research (Saint Petersburg) using the techniques of [11][12][13] and standards that are consis tent with those given in [14].…”

10th Applied Isotope Geochemistry Conference

“…We based our analytical development for Cr isotopes determinations on recent advances in digestion methods: an aliquot of 100 mg was submitted to a wet acid digestion (HNO 3 :HCl 3:1) using pressurized vessels at 240°C for a few hours (Paliulionyte et al, 2006). To ensure the complete digestion and verify potential nugget effect, the concentration results were validated by using the more established procedure of sintering (Na 2 O 2 , 450°C) on every samples as well as a set of chromitite standards and certified reference materials often used in the literature.…”