Coulometric determination of metal ions using Cu-diethylenetriaminepentaacetate complex as reactant

Abstract

In the determination of metal ions with a flow coulometric detector in liquid chromatography, mercuric complexes of diethylenetriaminepentaacetate (DTPA) or ethylenediaminetetraacetate (EDTA) have been used as a reactant because the detection is little interfered by dissolved oxygen in the sample solution and in eluent. From the view point of pollution, the use of mercury compounds is undesirable and cupric compound is more likely. Cu-DTPA was more stable than mercuric complexes as an electroanalytical reagent. However, the detection limit by Cu-DTPA was less than that of Hg(II)-complex. The variation of current efficiency of the electrochemical reaction for 20 days was 2.2%. Cu-DTPA complex with a satisfactory quality for the analysis was prepared by mixing CuSO₄-5H₂O (>99.5%) and DTPA (reagent grade). In the Cu-DTPA solution the amount of Cu should be between 100 and 101% (mol) of DTPA. The effect of electrolytic cell temperature on the optimum detection was examined and the temperatures above 20°C were suitable for the detection. The electrolytic efficiencies for Cu²⁺, Zn²⁺, Ni²⁺, Pb²⁺, Co²⁺ and Cd²⁺, separated with ion-exchange chromatography were measured. The efficiency for these ions except Ni²⁺ was almost 100% with Cu-DTPA. On the other hand, Cu-EDTA available commercially was poor reactant and the current efficiency was only (3080) %.