Electrosorption of Chromium-diethylenetriaminepentaacetic Acid on Mercury Electrode under Voltammetric Conditions

Abstract

Interfacial tension of the mercury electrode was measured in 0.1 M acetate buffer pH 6.2 containing Cr(III) and Cr(VI) at concentration ranging from 0 to 3×10−4 mol L−1 in presence of diethylenetriaminepentaacetic acid (DTPA) (Cr : DTPA in relation 1 : 1) under voltammetric conditions using the drop-time technique with long drop-times and controlled convection of the solution. The dependence of surface pressure and value of surface excess of Cr(III)-DTPA on concentration was determined at the constant potential −1000 mV (vs. saturated calomel electrode, SCE). Changes of interfacial activity of the Cr(III)-DTPA solution were found to obey approximately the Frumkin adsorption isotherm. The obtained dependences followed the hyperbolic or S-shaped curves at high concentrations of Cr(III) approaching the limits. In case that Cr(VI) was present in the bulk, its concentration changes caused at −1000 mV (SCE) very high surface pressure increase exhibiting a nonmonotonous shape. On the basis of their adsorption behavior the mentioned systems can be characterized as strongly adsorptive, affected in the case of Cr(VI) by the onset of the faradaic process. The presence of nitrates had a minor effect on the surface pressure π changes in Cr(VI)-DTPA solutions due to their catalytic effect in the corresponding measurements.