Abstract
A sensitive and relatively selective spectrophotometric method is proposed for the rapid determination of uranium using Eriochrome Black T (EBT) being a 2,2’-dihydroxy azo benzene derivative metal indicator in the presence of cationic surfactant of N-cetyl N,N,N-trimethylammonium bromide (CTAB). The complex formation reaction between EBT and uranyl ion, UO2 2+ is instantaneous in presence of NH3/NH4Cl buffer at pH 9.5 and the absorbance as analytical signal remains stable for over 6 h. CTAB as cationic surfactant and polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether, octyl phenol ethoxylate (Triton X-100) as nonionic surfactant are used for improving the sensitivity and solubility of the analytical system, respectively. The proposed method allows the determination of uranium in the concentration range of 0.025-2 μg mL–1 with a molar absorption coefficient of 92440.60 L mol–1 cm–1 and Sandell’s sensitivity of 2.92 μg cm2- in micellar medium while it allows the determination of uranium in the concentration range of 0.25-2.5 μg mL–1 with a molar absorption coefficient of 57019.44 L mol–1 cm–1 and Sandell’s sensitivity of 4.74 μg cm2- at 565 nm in water. The method has a detection limit of 4.60 μg L–1 (CDL: 3Sb/m) at an analytical measurement wavelength of 637 nm with a bathochromic shift of 72 nm. The selectivity of chelating reagent was improved by the use of a mixture containing ethylenediaminetetraacetic acid (EDTA), sulfosalycylic acid and NaF as masking agent. The proposed method has been successfully applied to the determination of uranium at trace levels in different environmental water samples such as tap-water, natural springwater and river-water. The precision (with coefficient of variation of 1.85%) and the accuracy obtained were highly satisfactory. In order to test the accuracy and validation of the method, the certified reference material (TMDA-70; fortified lake water sample) was also analyzed. It was found that the found and the certified values were in good agreement for validating the surfactant enhanced-spectrophotometric method.
Highlights
Uranium metal in its pure form is chemically active, anisotropic and has poor mechanical properties
The surfactants used were CTAB as cationic surfactant, Sodium dodecyl sulphate (SDS) as anionic surfactant and TritonX-100 as nonionic surfactant
This suggests that U(VI)-Eriochrome Black T (EBT) complex was dissolved in surfactant phase due to both forming ion-pairing complex with CTAB and the hydrophobic interaction of metal chelate
Summary
Uranium metal in its pure form is chemically active, anisotropic and has poor mechanical properties. A simple, sensitive, relatively selective, accurate and precise method for the determination of U(VI) in different water samples by spectrophotometry is described based on the formation of the U(VI)-EBT complex in the mixed surfactant medium. The use of CTAB as cationic surfactant leads to a maximum increase in the absorbance signal and as a result the analytical determination sensitivity is increased.
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