Synergistic Solid Phase Extraction of Ultra Trace Uranium by Mixtures of Dicyclohexyl-18-crown-6 and Tri-n-octylphosphine Oxide

Abstract

Ultra trace amount of uranium was extracted selectively by a simple and reliable method using C₁₈ membrane disks modified with mixtures of tri-n-octylphosphine oxide and dicyclohexyl-18-crown-6 and determined sensitivity with dibenzoylmethane (DBM) as a chromogenic reagent. Synergistic solid phase extraction of uranium with different ligands such as tri-n-octylphosphine oxide (TOPO), tri-n-butylphosphate (TBP), bis(2-ethylhexyl) phosphoric acid (HDEHP), tri-n-octylamine (TOA), 1,10-phenanthroline (Phen), 8-hydroxyquinoline (Hox), methyl isobutyl ketone (MIBK) and dicyclohexyl-18-crown-6 (DC18C6), was studied. Extraction efficiency and the influence of sample matrix, type and optimum amount of extractant and synergist, flow rates, and type and minimum amount of organic eluent were evaluated. In this method, most of the cations and anions have no interfering effect on the extraction and determination of uranium. However, effects of some interfering species such as Th(IV), Zr(VI), Mo(VI) and Cr(VI) were eliminated in the presence of proper masking and reducing agents such as EDTA, NH₂OH.HCl and F^– or rinsing of membrance disk before elution. The limit of detection of the proposed method is 0.003 μg/mL. Maximum capacity of the membrane disks modified by 40 mg of TOPO and 5 mg of DC18C6 was found to be 4563 ± 42 μg of U(VI). The method was applied to the extraction and determination of uranium in natural waters.