Selective Micellar Extraction of Ultratrace Levels of Uranium in Aqueous Samples by Task Specific Ionic Liquid Followed by Its Detection Employing Total Reflection X-ray Fluorescence Spectrometry

Abstract

A task specific ionic liquid (TSIL) bearing phosphoramidate group, viz., N-propyl(diphenylphosphoramidate)trimethylammonium bis(trifluoromethanesulfonyl)imide, was synthesized and characterized by H NMR,C NMR, P NMR, and IR spectroscopies, elemental (C H N S) analysis, and electrospray ionization mass spectrometry (ESI-MS). Using this TSIL a cloud point extraction (CPE) or micelle mediated extraction procedure was developed for preconcentration of uranium (U) in environmental aqueous samples. Total reflection X-ray fluorescence spectrometry was utilized to determine the concentration of U in the preconcentrated samples. In order to understand the mechanism of the CPE procedure, complexation study of the TSIL with U was carried out by isothermal calorimetric titration, liquid-liquid extraction,P NMR and IR spectroscopies, and ESI-MS. The developed analytical technique resulted in quantitative extraction efficiency of 99.0 ± 0.5% and a preconcentration factor of 99 for U. The linear dynamic range and method detection limit of the procedure were found to be 0.1-1000 ng mL and 0.02 ng mL, respectively. The CPE procedure was found to tolerate a higher concentration of commonly available interfering cations and anions, especially the lanthanides. The developed analytical method was validated by determining the concentration of U in a certified reference material, viz., NIST SRM 1640a natural water, which was found to be in good agreement at a 95% confidence limit with the certified value. The method was successfully applied to the U determination in three natural water samples with ≤4% relative standard deviation (1σ).

Selective Liquid‐Liquid Extraction of Uranium by Phosphoramidate‐Group Bearing Ionic Liquid

“…The recorded IR spectra are given as Figure . It had been previously established by our group that maximum two TSIL molecules get coordinated to each U(VI) in solution . The shift in TSIL P=O stretching frequency from 1228 cm −1 to 1126 cm −1 (Figure ) on complexation with U is in accordance with the literature reported values .…”

“…are the first to explain the extractability of a phosphoramidate group bearing TSIL for U(VI) with a maximum D U value of 177 . A phenyl derivative of their compound viz., N‐propyl(diphenylphosphoramidate)trimethylammonium bis(trifluoromethane‐sulfonyl)imide or [phamdNMe 3 ][NTf 2 ], has been previously synthesized in our laboratory . Considering the fact that compared to the dibutylphosphoranidate of Ouadi et al .…”

Trace determination of uranium preconcentrated using graphene oxide by total reflection X‐ray fluorescence spectrometry

“…The MDL of the methodology was found to be comparable with previously reported TXRF‐based works using other preconcentration procedures . The MDL of these measurements have been 0.8, 0.067, and 0.02 μg L −1 , with preconcentration by using membrane‐containing complexing reagents with a 50‐ml sample, extractant of diethyl ether with a 50‐ml sample, and ionic liquid for cloud point extraction with a 7.5‐ml sample . These previously reported TXRF analyses were performed using large‐scaled instruments with high‐power X‐ray tubes (operated with 1,100 W for the membrane‐based method or 1,200 W for the other method) and counting time of 400 s for the membrane‐based method or 1,000 s for the other method.…”

“…The MDL increased with increasing ionic strength because the background intensity derived from scattered X‐rays caused by a small sodium salt spot on the fluorine resin‐coated slide glass increased with increasing ionic strength, which results in matrix effects . The MDL of the methodology was found to be comparable with previously reported TXRF‐based works using other preconcentration procedures . The MDL of these measurements have been 0.8, 0.067, and 0.02 μg L −1 , with preconcentration by using membrane‐containing complexing reagents with a 50‐ml sample, extractant of diethyl ether with a 50‐ml sample, and ionic liquid for cloud point extraction with a 7.5‐ml sample .…”

“…Uranium detection by means of total reflection X‐ray fluorescence (TXRF) spectrometer has been applied to water samples preconcentrated by using membrane containing complexing reagents, extractant of diethyl ether, and ionic liquid for cloud point extraction . These TXRF analyses were performed using large‐scaled instruments with high‐power X‐ray tubes (operated with 1,100 or 1,200 W), demanding water‐cooling systems and silicon drift detectors.…”