The noise power spectra of 85Rb+ signal and MNb+ signal from an Inductively coupled plasma mass spectrometer were measured at the same plasma conditions as were those of Sr II emission from the plasma Itself. Comparison of these spectra showed that discrete frequency noise In the emission at the mass spectrometer sampling orifice Is nearly Identical with that In the mass spectrometrlc signal and that white noise In the mass spectrometer signal was higher than that found In the emission signal. The dependence of noise frequencies on plasma operating conditions was generally the same for both measurements and was generally the same as that expected of emission from the plasma alone, l.e., when the plasma was not being sampled for mass spectrometry. However, discrete frequency noise In emission from the plasma alone differed substantially In frequency from that in the mass spectrometrlc signal. These results Indicate that the plasma Is the source of discrete frequency noise In the mass spectrometrlc signal and that the discrete noise frequencies can be affected by changes In plasma gas dynamics due to interaction between the plasma and the mass spectrometer sampling Interface. The major source of signal Instability In this particular Inductively coupled plasma mass spectrometer was found to be 1H noise.

Inductively coupled plasma-mass spectrometry (ICP-MS) was used to concurrently determine multiple long-lived (t_ > 104 y) actinide isotopes in soil samples. Ultrasonic nebulization was found to maximize instrument sensitivity. Instrument detection limits for actinides in solution ranged from 50 mBq L-I (ngPu) to 2 _Bq L-I (23SU). Hydride adducts of n2Th and 238U interfered with the determinations of 233U and 239pu; thus, extraction chromatography was used to eliminate the sample matrix, concentrate the analytes, and separate uranium from the other actinides. Alpha spectrometric determinations of 23°Th, ngPu, and the 234U/nsU activity ratio in soil leachates compared well with ICP-MS determinations; however, there were some small systematic differences (ca. 10%) between ICP-MS and _-spectrometric determinations of 234U and 238U activities.

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