Straightforward determination of U, Th, and Hf at trace levels using ultrasonic nebulization and axial view ICP OES

Abstract

Inductively coupled plasma optical emission spectrometry (ICP OES) is applied for direct determination of U, Th and Hf in environmental and geological samples (phosphate rock, soil, sediment, bush branches and leaves, and natural water). Several spectral lines and sample decomposition procedures were investigated with respect to spectral and non-spectral interference. For U and Hf determination, the geological sample treatment required hydrofluoric acid, whereas Th could be accurately determined in the samples decomposed by aqua regia solely. Ultrasonic nebulization (USN) and pneumatic nebulization with aerosol desolvation (PN-DES), with and without a microporous membrane, were evaluated for introducing the sample solution into the ICP. Better results were obtained by using USN; the limits of detection for U (U II 409.014 nm), Th (Th II 401.913 nm) and Hf (Hf II 264.141 nm) were 0.03, 0.01, and 0.01 μg g⁻¹, respectively. Uranium, Th and Hf were precisely and accurately determined without matrix separation/analyte pre-concentration; the relative standard deviation (RSD) was typically <7% and the recovery of the analytes in the certified reference materials (phosphate rock, soil, sediment, bush, branches and leaves, and natural water) ranged from 83 to 112%. These results were linked to careful selection of spectral lines, which depended on the sample matrix and reagents used for sample decomposition.