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 v ary to a large extent by the fluctuations in oxygen pressure in the io n source of the mass spectrometer and that the stability of oxygen pre ssure 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 indispensabl e 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 correspondi ng calculated atomic weight of Re is 186.206747 +/- 0.000019, which is much more precise than the preciously reported values. (C) 1998 Elsev ier Science B.V.