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 waters and sediments by isotope dilution inductively coupled plasma mass spectrometry (ID-ICPMS). The techniques have been applied to determination of the three elements in sediments, Pt in seawater, and Re in seawater, sediment pore waters, and river waters. In each case, a stable isotope-enriched spike is added to the sample before processing. Sediments are dissolved in all-Teflon digestion vessels using a modified standard 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 molecular ions in the argon plasma resulting in isobaric interferences. Samples are then introduced into the ICPMS in a small volume (300-600 muL) using flow injection. Overall recoveries were 90 +/- 10% for all three elements, although the effects of variable recovery efficiency were minimized by the isotope dilution technique. The method has detection limits (3 times background) of approximately 5 pg of Re, 6 pg of Ir, and 14 pg of Pt.