Electrochemical Determination of Adsorption Isotherm of Mordant Red 19 on Mercury and Its Analytical Application for the Indirect Determination of Uranium

Abstract

A voltammetric method for the determination of trace level of uranium is described. The method is based on an adsorptive accumulation of the uranium-Mordant red 19 (MR19, 4-[(5-chloro-2-hydroxy-3-sulfo-phenyl)azo]-5-hydroxy-3-methyl-1-phenyl-pyrazole, sodium salt) complex on a hanging mercury drop electrode followed by the reduction of the adsorbed complex. A detection limit of 8.0×10–11 M uranium can be obtained with a controlled adsorptive accumulation for 10 min. A linear response is obtained from 4.0×10–8 M to 5.0×10–6 M concentration of uranium with the relative standard deviation of 3.9 % at 5.0×10–8 M uranium. The interfacial and redox behavior are characterized by cyclic voltammetry. Chronocoulometry has been used to evaluate the surface coverage vs. the concentration of MR19 in 0.05 M KHP buffer. The surface excess obeys Langmuir isotherm over the concentration range from 1.0×10–8 M to 1.0×10–6 M with a saturation limit of 1.08×10–10 mol/cm2, which corresponds to the cross-sectional area of 154 Å2 /molecule. The effect of various operational parameters on the stripping response is discussed. Also interferences from other metal ions are examined.