Direct Spectroscopic Determination of Europium (II) Concentration During Europium (II) Electro-Reduction in Hydrochloric Acid Medium

UV-Vis spectroscopy was used to directly determine the concentration of Eu (II) during electroreduction of Eu (III) in hydrochloric acid medium. Electroreduction was carried out in a flow type electrolyzer with glassy carbon cathode at the constant potential of - 800 mV vs. Ag/AgCl. The effects of oxygen and concentration of hydrochloric acid on the system were investigated. For 0.01 mol·L^-1 hydrochloric acid, calibration curves for Eu (II) absorption bands at 248 and 320 nm were constructed. Molar absorption coefficients were estimated to be 2016 and 648 L·mol^-1 · cm^-1, respectively. The absorbance strongly decreased with decrease in pH of the solution, whereas concentration of chloride had only a negligible effect.