APPLICATION OF RADIOACTIVE-TRACERS FOR INVESTIGATION OF DYSPROSIUM AND MANGANESE VAPORIZATION IN ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

Radioactive tracers Dy-165 and Mn-56 have been used to investigate the vaporization of Dy and Mn in a graphite furnace. The retention and distribution of the analytes after atomization in pyrolytic graphite coated electrographite (PCG) tubes have been measured and the efficiencies of Dy and Mn vaporization have been compared for wall, platform and probe atomization in total pyrolytic graphite (TPG) tubes. Manganese is vaporized almost completely (95-100%) at 2500-degrees-C by each of the atomization modes, with little retention at the point of initial deposition. Manganese is redeposited at the very ends of the PCG tube and the amount of redeposition increases with the age of the tube. Total pyrolytic graphite (TPG) exhibits lower redeposition of Mn than does PCG and the deposition is mainly on the outside of the tube. Dysprosium is almost totally retained in PCG and TPG tubes. Vaporized Dy is redeposited very rapidly, mainly at the centre of the tube, and causes a memory effect in subsequent heating cycles. About 60% of the Dy is vaporized from the probe at 2750-degrees-C, whereas only 7% is vaporized from the platform. The difference in the vaporization efficiencies is reflected in the atomic absorption spectrometric sensitivities for both procedures. Wall atomization gives the best sensitivity for Dy, but is only 1.5-fold better than for probe atomization. Some comments are given on the possible mechanisms of Dy vaporization and atomization, but mass spectrometry studies are required to give a clearer explanation of the phenomena.