Sensitive Spectrophotometric Determination of U(VI) Ion at Trace Level in Water Samples: A Simple and Rapid Homogenous Solvent-Based/In-Situ Solvent Formation Microextraction Based on Synthesized/Characterized Task-Specific Ionic Liquid

Abstract

The preconcentration of uranium VI (U(VI)) at trace levels in some real water and wastewater samples and its determination by spectrophotometry using a homogeneous solvent-based microextraction method, specifically in-situ solvent formation microextraction, were investigated. This microextraction method uses a unique task-specific ionic liquid (IL) as the specific complexing agent and/or extracting phase. A pyrrolidinium-based IL modified with (E)-5-(bromomethyl)-2-(pyridin-2-yldiazenyl) phenol as a task-specific IL (E)-1-(3-hydroxy-4-(pyridin-2-yldiazenyl) benzyl)-1-methylpyrrolidinium bromide (TSIL/Br) was successfully synthesized and characterized by ¹HNMR and FTIR analyses. TSIL/Br chelated with U(VI) ions in the aqueous phase to form a hydrophilic [U(VI)-TSIL/Br₂] complex with high efficiency. It was then converted to a hydrophobic [U(VI)-TSIL/(NTf₂)₂] complex through a counter-ion agent, such as bis(trifluoromethanesulfonyl)imide (\(\text{NTF}_2^-\)) for separation from the aqueous solution phase. This process eliminates the need for a separate complexing agent, because TSIL/Br acts simultaneously as both a complexing agent and an extracting solvent. In brief, the conditions of the microextraction process must be optimized for the analysis of real water samples. Under the optimum conditions, a preconcentration factor, detection limit, quantification limit, linear dynamic range, and relative standard deviation of 218, 1.62 ng·mL⁻¹, 5.42 ng·mL⁻¹, 20.0–450.0 ng·mL⁻¹, and 2.47% (n = 10, 20 ng·mL⁻¹) were obtained, respectively. Finally, to assess the method’s ability, it was successfully employed to determine the U(VI) ion content in various real water, wastewater and reference material samples.