Determination of trace amounts of Eu 3+ and Yb 3+ ions at Nafion-coated thin mercury film electrodes

Abstract

The use of Nafion-coated thin mercury film electrodes (NCTMFE) for determining trace amounts of Eu 3+ and Yb 3+ ions was examined. Ion-exchange preconcentration of submicromolar levels of the two rare earths was achieved efficiently at a rotating NCTMFE, while the use of “classical” Nafion-coated glassy carbon electrodes is restricted to the determination of Eu 3+ alone. Differential-pulse voltammetry was used to quantify the accumulated ions. The influence of variables such as rotation rate, preconcentration time and scan parameters was assessed. A preconcentration -voltammetry-regeneration scheme suitable for multiple analysis with the same modified electrode was developed. Calibration graphs with a linearity range extending up to 2 μM and detection limits of 0.03 and 0.08 μM for Eu 3+ and Yb 3+, respectively, were obtained. For Yb 3+, the detection limit can be lowered to 0.02 μM by electrocatalytic amplification of the signals achieved by operating in the presence of ammonium nitrate as supporting electrolyte. However, in this instance a more restricted linearity range is observed. The effect of competing incorporation caused by the presence in solution of an excess of La 3+ is also discussed, together with the competition between Eu 3+ and Yb 3+ when one of the two is present in large excess over the other.