Coprecipitation as a one-step Se separation for determination of isotope ratios completed with revised uncertainty evaluation

Selected geological and biological reference materials were analyzed. These include the United States Geological Survey Reference Materials SGR-1 (oil shale, Green River Formation), SCo-1 (cody shale), MAG-1 (marine mud), European Reference Materials BC210a (selenized wheat flour), and selenium-enriched yeast-certified reference material SELM-1.These SRMs were analyzed: NIST SRM 3149 with the addition of a matrix, artificial seawater, and NASS-4 standard seawater spiked with NIST SRM 3149, SELM-1 and BC210a. In addition, the following geological standards were analyzed: SGR-1, SCo-1 and MAG-1.Selenium isotope ratios were measured at the Biological and Chemical Research Centre of the University of Warsaw using the Plasma 3 multicollector ICP mass spectrometer with 16 Faraday cups (Nu Instruments, Wrexham, U.K.). Three isotopes (77Se, 78Se, and 82Se) were chosen for isotope ratio measurements. Three of the Faraday collectors, H8 (82Se), Ax (78Se) and L2 (77Se), were set to register the signals and mass separation of 0.5 atomic mass unit was applied. All data sets reported in this files were collected between April and July 2023.The HGX-200 advanced membrane hydride generation system was applied for sample introduction to MC instrument. The instrument was running in dry plasma mode. The Time-Resolved Analysis (TRA) mode was used for gathering experimental data.The selenium isotope ratios were determined using the SSB method by sequential measurements of the standard-sample-standard. Such external calibration with NIST SRM 3149 provides the delta value. The results are expressed as δ.The sensitivity we achieved was >1 V 78Se per 100 μg/L. All samples were diluted to total Se content around 100 μg/L, except for the NASS-4 sample which was spiked at level 50 μg/L.