Determination of lead in rocks by radiometric isotope dilution and substoichiometric extraction

A rapid procedure is described for the determination of lead in rocks by an isotope-dilution substoichiometric method. After the sample has been digested with acid in the presence of ²¹⁰Pb tracer, the lead is separated by dithizone extractions. After the lead has been back-extracted into aqueous solution, it is reacted with a substoichiometric amount of EDTA. Excess of unreacted lead is removed by extraction with dithizone in carbon tetrachloride, and the specific activity of the aqueous complex is determined by counting ²¹⁰Pb. The standard deviation of the method is less than 10 % for replicate determinations of lead in several U.S. Geological Survey standard rocks. The agreement with literature values indicates that the method is accurate.