Abstract
A microanalytical procedure for the separation of Pb and U and their determination by isotope dilution-mass spectrometry is described. It is shown that high precision isotopic analysis of as little as 8 X 10^(11) Pb atoms is readily achievable. The level of Pb contamination is reduced to as little as 4 X 10^(10) atoms and the blank fluctuation is controllable. In the special case where the chemical separation could be omitted, 4 X 10^(10) Pb atoms were isotopically analyzed with a blank correction of 6 X 10^9 Pb atoms. This procedure was applied to a 0.2-mg lunar sample containing 2.5 ppm Pb and 1 ppm U and the U-Pb isotopic measurements obtained are Fully compatible with measurements on large samples. In addition, Pb on the surface of individual lunar glass balls of 150-300 µm diameter was measured. Extension of this approach to other heavy metals may be possible.
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