Selective Determination of Europium(III) Oxide and Hydroxide Colloids in Aqueous Solution by Laser-Induced Breakdown Spectroscopy

Abstract

Laser-induced breakdown spectroscopy (LIBS) was applied to selectively analyze the aqueous suspension of Eu2O3(s) particles in the presence of the Eu3+ aquo ion. A plasma was generated by focusing a pulsed Nd:YAG laser beam (λ = 532 nm) into the sample. The light emission from the plasma was detected by a spectrograph equipped with a gated intensified charge-coupled device (ICCD) in the wavelength range of 275–525 nm. The atomic emission intensity of the Eu2O3(s) suspension was about two orders of magnitude higher than that of the Eu3+ aquo ion. The detection limits for Eu3+(aq) and Eu2O3(s) were found to be 3.3 × 10−5 mol/L and 2.0 × 10−7 mol/L, respectively. Such a difference allows the selective determination of colloidal europium particles. This capability of LIBS was used to study the formation of Eu(OH)3(s) colloids in the aqueous Eu3 solution by varying pH until the solubility limit was exceeded. The appraisal of the threshold pH for the solubility limit led to the determination of the solubility product of colloidal Eu(OH)3(s), which was then calculated to be log K0sp= −25.5 ± 0.4.