A high-throughput method for the determination of Os concentrations and isotope ratio measurements in small-size biological samples

Abstract

An analytical method allowing multi-element characterization by external calibration, osmium (Os) concentration determination by isotope dilution (ID) and ¹⁸⁷Os/¹⁸⁸Os isotope abundance ratio measurement from a single sample preparation was developed. The method consists of microwave-assisted, closed-vessel acid digestion of small (0.01–0.4 g dry weight) biological samples spiked with Os solution enriched in a ¹⁹⁰Os isotope followed by concentration and Os isotope ratio measurements using double-focusing, sector field inductively coupled plasma mass-spectrometry (ICP-SFMS) operated with methane addition to the plasma and solution nebulization (SN) sample introduction. For samples with Os content below 500 pg, complementary analysis using gas-phase introduction (GPI) on the remaining sample digests was performed. The use of disposable plastic lab ware for sample digestion and analysis by SN ICP-SFMS circumvents Os carry-over effects and improves the sample throughput and cost-efficiency of the method. For a 0.1 g dried sample, Os method limits of detection (MLODs) of 2 pg g⁻¹ and 0.2 pg g⁻¹ were obtained using SN or GPI, respectively. Long-term reproducibility of ¹⁸⁷Os/¹⁸⁸Os isotope abundance ratio measurements using the GPI approach was better than 1.5% RSD for our in-house control sample (moose kidney) with an Os concentration of approximately 5 pg g⁻¹. Os data for several commercially available reference materials of biological or plant origin (not certified for Os) are presented. The method was used in the large scale bio-monitoring of free-living bank voles from an area affected by anthropogenic Os emissions.