In the determination of lead in monazite-to be used as the basis for geologic age measurements-it was necessary to eliminate interferences due to the presence of phosphates of thorium and the rare earth metals. The method involves attacking the monazite samples with hot, concentrated sulfuric acid, then taking them up with dilute nitric acid. Lead is extracted as the dithizonate and determined spectrophotometrically at 520 m??. Rapid determinations were made with good reproducibility on a series of monazite samples.
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Dithizone method for determination of lead in monazite