The selective separation of thorium from uranyl ions using ultrasonic-assisted solidified floating organic drop microextraction

Abstract

The accurate determination of thorium (Th⁴⁺) in the presence of uranyl ions (UO₂²⁺) is a challenge facing analytical chemists. In this article, a solidified floating organic drop microextraction procedure (SFODME) combined with inductively coupled plasma-optical emission spectrometry (ICP-OES) is presented for the separation of Th⁴⁺ from UO₂²⁺. Morin (2′,3,4′,5,7-pentahydroxyflavone) selectively forms a stable complex with Th⁴⁺ in an acidic medium (pH 2.5), while UO₂²⁺ does not. The formed complex can be separated into an organic drop of 1-undecanol in the presence of ethanol as a dispersive solvent. The major factors influencing the achievement of SFODME, that is, pH, morin concentration, the type and volume of the extracting and dispersive solvents, the sonication conditions, the ionic strength, and the presence of foreign ions, were investigated. Under optimum conditions, the calibration graph was linear in the range of 0.3–400.0 μg L⁻¹. The detection limit and enrichment factor values were 0.12 μg L⁻¹ and 31.1, respectively. The relative standard deviation for 12 replicates was 1.5%. No significant effects from potentially interfering species, including f-block elements, were observed. The procedure was effectively applied for the determination of Th⁴⁺ in phosphate rock and ceramic tile samples.