Efficient N-TIMS rhenium isotope measurements on outgassed tantalum filaments: very low filament blanks determined by a 'standard addition' approach

摘要

We have successfully tested two sets of Ta filaments for their suitability to measure Re isotopes by negative thermal ionization mass spectrometry. No significant Re contribution from the filament material itself could be detected. Therefore Ta filaments are a viable, low cost alternative to high purity Pt filaments which are commonly used for Re-Os isotope analyses. A technique whereby Re is directly loaded with H2SO4 into Ba(NO3)2 and precipitated together with BaSO4 on the filament has resulted in stable and constant ion beams. Furthermore, slight oxidation of the Ta filament surface significantly facilitates point loading in the center of the filament. The BaSO4 loading technique has proved to be less sensitive towards time-consuming pre-analytical heating procedures than Ba(NO3)2 on Pt filaments. Furthermore, Re isotopic ratios remained constant over a wider range of measuring temperatures, in contrast to what we observed during Re analysis from Pt filaments loaded with Ba(NO3)2 or BaSO4.