Radiotracer study of the electrophoretic behavior of Eu and its complexes with humic acid

Abstract

Humic acid / Europium / Radiotracer method / Electrophoresis / ComplexationSummary. The interaction of Eu with purified/protonized Aldrich humic acid (HA) was studied by the free liquid/ moving boundary electrophoresis used in combination with the radiotracer method. Introductory experiments were carried out to test electrophoretic behavior of Eu in HA-free solutions, and to determine mobility of Eu 3+ cation. To get the data for evaluation of parameters describing Eu binding to HA, titrations of HA (10 mg/L) with Eu were performed batchwise in the range 3.4 × 10 −8 -1.7 × 10 −3 M of Eu total concentration at pH 3, 4, 5 and 6, and 0.01 M ionic strength (NaClO 4 ). In each batch, the degree of Eu complexation with HA was determined from 152 Eu electrophoretic mobilities in the cathodic direction. The experimental data were fitted with a discrete site model (Scatchard plot-like model) with two types of carboxylic sites. An additional information on the charge characteristics of the Eu-HA complexes has been obtained from the 152 Eu anodic mobilities.

Application of radiotracer techniques to a kinetic study of the interaction of Eu with humic acid

“…The method of the free liquid/moving boundary electrophoresis and its instrumentation was described in detail elsewhere (e.g., [14]). It is possible to determine the degree of complexation of metal by HA from the decrease of its effective cathodic mobility observed in the presence of the complexing agent, while the anodic mobility is indicative of the negative charge of the metal-HA complexes formed [15]. The method was used in two experimental modes allowing to observe electromigration of 152 Eu (i.e., both free Eu 3+ and Eu bound to HA) by measuring activity of the samples from the cell compartments, or by measuring absorbance of the samples to follow electromigration of HA and/or Eu-HA complexes.…”

Isotope exchange study of the dissociation of metal —humic substance complexes

“…Complexation was studied previously under similar conditions (10 mg L -1 AHA, I = 0.01) by electrophoresis. For Eu-AHA, at [Eu]0 = 2 x 10 -5 mol L -1, > 90 % Eu was complexed at pH 6 and -70 % Eu at pH 4 [6]. For Co-AHA, 97 % and 51% Co was complexed at pH 6, [Co]0 = 1 x 10 -7 and 1 x 10 -5 mol L -1, respectively, while only 23 % and 13 % Co at pH 4 and the same loadings [7].…”

A new technique for radiolabelling of humic substances

“…A promising way to overcome these limitations is the application of radionuclides. Metals are often used as radiotracers in terms of investigation of the metal complexation with HS [5][6][7][8][9]. Focusing on the physicochemical properties of the HS another method is needed to preclude denaturing effects and to maintain the HS-functionalities unchanged.…”