DETERMINATION OF RHENIUM AND PLATINUM IN NATURAL-WATERS AND SEDIMENTS, AND IRIDIUM IN SEDIMENTS BY FLOW-INJECTION ISOTOPE-DILUTION INDUCTIVELY COUPLED PLASMA-MASS SPECTROMETRY

Methods have been developed to measure Re, Ir, and Pt in natural water s and sediments by isotope dilution inductively coupled plasma mass sp ectrometry (ID-ICPMS). The techniques have been applied to determinati on of the three elements in sediments, Pt in seawater, and Re in seawa ter, sediment pore waters, and river waters. In each case, a stable is otope-enriched spike is added to the sample before processing. Sedimen ts are dissolved in all-Teflon digestion vessels using a modified stan dard kitchen microwave oven. Anion exchange of the chloro complexes of Ir and Pt and of the perrhenate ion (ReO4-) is used to preconcentrate the elements and to separate them from concomitants which produce mol ecular ions in the argon plasma resulting in isobaric interferences. S amples are then introduced into the ICPMS in a small volume (300-600 m uL) using flow injection. Overall recoveries were 90 +/- 10% for all t hree elements, although the effects of variable recovery efficiency we re minimized by the isotope dilution technique. The method has detecti on limits (3 times background) of approximately 5 pg of Re, 6 pg of Ir , and 14 pg of Pt.