Atomic Absorption Spectrometry of Ytterbium Using Carbon Tube Atomizer; an Application to Phosphate Minerals

Abstract

Atomic absorption spectrometry using a carbon tube atomizer was applied for the determination of ytterbium in phosphate minerals such as xenotime, monazite, and apatite. A constant absorption signal of ytterbium was observed above ca. 2650 °C in carbon tube. In the present experiments, the carbon tube atomizer was operated at an atomizing temperature of ca. 2700 °C where the current was 300 A for 10 s. In the ytterbium concentration range of (10~40) ppb in the sample solution, a fairly linear calibration curve was obtained. when 10 µl of the solution was injected. The sensitivity (1 % absorption) was 1.35 ppb, and the R. S. D was ca. 7 %. The effect of coexisting salts on the peak absorbance of ytterbium was examined with regard to the solution of 35 ppb ytterbium containing (101~104) times equivalent amounts of the salts. The peak absorbance of ytterbium was only slightly affected by (101~103) times equivalent amounts, but by 104 fold amounts, most salts interfered. Phosphate minerals were treated with hot concentrated sulfuric or nitric acid. After any insoluble residue was filtered, the filtrate was diluted with water until the concentration reached to (1~20)µg/ml with respect to xenotime or monazite. Ten microliters of these sample solutions were directly injected into the carbon tube atomizer. By this analysis, the content of ytterbium in these minerals was found to be (0.19~2.18)%. However, direct determination of ytterbium in calcium apatite mineral was difficult because of an interference of calcium ions. Therefore, ytterbium content in such an apatite was determined after ytterbium extracted from 10 M perchloric acid containing 0.1 M di- (2-ethylhexyl) phosphate (HDEHP) into cyclohexane, the amount found was in the range of the 2.26X10-3% to 2.56X10-3%. © 1982, The Japan Society for Analytical Chemistry. All rights reserved.