Analytical application of ionic liquid in determination of trace metallic constituents in U matrix by ICP-OES: A 'green' approach for drastic reduction in organic waste burden and time of analysis

Abstract

Selective chemical separation of U without any compromise of analyte concentration even at trace level; is a prerequisite to avoid the spectral interference in Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). “Green” approach based on application of ionic liquid; has been followed to bring down the U concentration below the tolerance limit, prior to the analyses of common metallic constituents (Al, Ca, Cu, Cr, Fe, Mn, Mg, Na, Ni, Pb, and Zn) and critical elements (B, Cd, Ag, Eu, Sm, Gd, and Dy). 'Anion exchange' mechanism was found to be predominantly operative for TBP/C3PyNTf2 based separation system during extraction of U, involving 1:2 anionic metal–ligand complex; while, in TBP/n-dodecane, conventional 'solvation' mechanism was operative involving 1:2 neutral metal–ligand complex. The methodologies were optimized (identification of interference free analytical lines, establishing calibration curves, estimation of detection limits, linear dynamic range, precision) using synthetic samples. Statistical t-test was performed to understand reliability of the data. Significant reductions in organic waste volume and sample processing time have been demonstrated by application of ionic liquids. For analysis of common analytes, three contacts of 1.1 M TBP/C3PyNTf2/6M HNO3 were found to be efficient in bringing down the U below tolerance level without much compromise on the concentrations of analytes at trace level. The associated error was within the limits of allowed statistical fluctuation. However, for critical elements, the methodology was not reliable. For them, the sample feed solution should be adjusted to 3 M HNO3 prior the U removal.