High-precision determination of osmium and rhenium isotope ratios by in situ oxygen isotope ratio correction using negative thermal ionization mass spectrometry

The Os and Re isotope ratios were determined from the measurements of OsO3- and ReO4- ions by negative thermal ionization mass spectrometry. It was found that the oxygen isotope ratios of OsO3- and ReO4- ions vary to a large extent by the fluctuations in oxygen pressure in the ion source of the mass spectrometer and that the stability of oxygen pressure and the in situ correction for the interference of (OsO2O-)-O-16-O-17, (OsO2O-)-O-16-O-18 and (ReO3O-)-O-16-O-18 ions are indispensable to the high-precision determination of Os and Re isotope ratios. The precision of Os-184/Os-188 ratio is further improved to about 0.1% in relative standard deviation if the interference of the (PtO2-)-Pt-192 ion with the (OsO3-)-Os-184 ion was taken into account. The (187)Rel(185)Re ratio was determined as 1.67389 +/- 0.00014 and the corresponding calculated atomic weight of Re is 186.206747 +/- 0.000019, which is much more precise than the preciously reported values. (C) 1998 Elsevier Science B.V.