Determination of Ultra Trace Amounts of Uranium (VI) by Adsorptive Stripping Voltammetry Using L-3-(3, 4-dihydroxy phenyl) Alanine as a Selective Complexing Agent

Abstract

The spectrophotometric behavior of uranium (VI) with L-3-(3, 4-dihydroxy phenyl) alanine (LDOPA) reagent revealed that the uranium can form a ML₂ complex with LDOPA in solution. Thus a highly sensitive adsorptive stripping voltammetric protocol for measuring of trace uranium, in which the preconcentration was achieved by adsorption of the uranium-LDOPA complex at hanging mercury drop electrode (HMDE), is described. Optimal conditions were found to be a 0.02 M ammonium buffer (pH 9.5) containing 2.0 × 10⁻⁵ M (LDOPA), an accumulation potential of − 0.1 V (versus Ag/AgCl) and an accumulation time of 120 sec.

The peak current and concentration of uranium accorded with linear relationship in the range of 0.5–300 ng ml⁻¹. The relative standard deviation (at 10 ng ml⁻¹) is 3.6% and the detection limit is 0.27 ng ml⁻¹. The interference of some common ions was studied. Applicability to different real samples is illustrated. The attractive behavior of this reagent holds great promise for routine environmental and industrial monitoring of uranium.

Keywords:

• Adsorptive stripping voltammetry
• LDOPA
• Uranium

Notes

Note. U(VI) = 10 ng ml⁻¹, [LDOPA] = 2 × 10⁻⁵ M, E_ac = − 0.1 V, accumulation time = 120 sec.

^a Maximum concentration of foreign species tested.

^b After addition of 100 µl of 0.001 M EDTA solution as masking agent.

^a Containing Ag⁺, Cu²⁺, Co²⁺, Cd²⁺, Zn²⁺, and Cr³⁺ (500 ng ml⁻¹); Pb²⁺ and Fe³⁺ (200 ng ml⁻¹); and 5.0 × 10⁻⁵ M EDTA.

^b A solution containing CN⁻, HPO₄ ^2-, SO₄ ^2-, CO₃ ^2-, Bi³⁺, Ag⁺, Mn²⁺, Cr³⁺ (500 ng ml⁻¹).