DETERMINATION OF LONG-LIVED ACTINIDES IN SOIL LEACHATES BY INDUCTIVELY-COUPLED PLASMA - MASS-SPECTROMETRY

Inductively coupled plasma - mass spectrometry (ICP-MS) was used to concurrently determine multiple long-lived (t(1/2) > 10(4) y) actinide isotopes in soil leachates. Ultrasonic nebulization was found to maximize instrument sensitivity. Instrument detection limits for actinides in solution ranged from 50 mBq L(-1) (Pu-239) to 2 mu Bq L(-1) (U-235). Hydride adducts of Th-232 and U-238 interfered with the determinations of U-233 and Pu-239; thus, extraction chromatography was used to concentrate the analytes and separate uranium from the other actinides in advance of mass spectrometric determination. Alpha spectrometric determinations of Th-230, Pu-239, and the U-234/U-238 activity ratio in soil leachates compared well with ICP-MS determinations; however, there were some small systematic differences (ca. 10%) between ICP-MS and alpha-spectrometric determinations of U-234 and U-238 activities. These differences were attributed to the use of different isotope dilution spikes for ICP-MS and alpha-spectrometry.