Uranium determination in groundwater using laser spectroscopy

Abstract

The aim of this work is to review the laser-based analytical techniques for the quantitative determination of uranium in aqueous solutions. Among the various types of laser-based analytical techniques, two different spectroscopic techniques based on the measurement of laser-induced luminescence of hexavalent uranium ions [U(VI)] in groundwater are reviewed in detail. In the first technique, called time-resolved laser fluorescence spectroscopy, the time-resolved laser-induced luminescence intensities of U(VI) as a function of uranium concentration are measured to obtain the calibration curve. In the second technique, which is based on the simultaneous measurement of the U(VI) luminescence and Raman scattering of water, the calibration curve is obtained by measuring the ratio of the luminescence intensity of U(VI) to the Raman scattering intensity of water for the quantitative determination of uranium. A limit of detection of 0.03 μg/l was achieved at an excitation wavelength of 266 nm using these laser spectroscopic techniques. The results determined using these techniques are in good agreement with the results determined by inductively coupled plasma mass spectrometry (ICPMS). Thus, these laserbased analytical techniques will be useful to personnel requiring a rapid determination of uranium before the shipment of samples to an accredited laboratory, where relatively intricate and expensive apparatuses, such as ICPMS and radiochemical spectrometry, are used.

Quenching Mechanism of Uranyl(VI) by Chloride and Bromide in Aqueous and Non-Aqueous Solutions

“…The deconvoluted time traces (Figures S3 and S4) give insights on how the involved electronic states and species are interconnected. A general mechanistic scheme based on our previous findings 23 can be seen in Figure 4: While the three electronic states of each complex ( 1 Σ ground state, 3 Φ and 3 Δ excited states) are coupled via excitation, internal conversion, and intersystem crossing processes from electron orbital transitions, the complexes themselves are coupled via halide addition or abstraction kinetics, that is, complexation.…”

“…This redox step is very rapid in comparison to the complex formation rate (k 15 ≫ k 9 ), but via a return reaction (k 16 ), a stable equilibrium between the oxidized form (radical ion pair) and the 3 Δ state of the [UO 2 Cl 2 ] 0 forms, which lies strongly on the side of the oxidized form (k 15 > k 16 ). After this equilibrium is established, the radical ion pair complex of UO 2 + and X 2 •− will separate into their respective fully separated and solvated ions and no luminescent 3 Δ is accessible again (k r ≪ k 17 = 2.2 and 2.9 ns −1 , respectively). As this "separation" rate is the slowest in the whole process, it can be considered as the dominant rate competing with k r and can be compared to the macroscopically observable quenching rate k q in luminescence spectroscopy.…”

“…Time-resolved laser-induced fluorescence spectroscopy (TRLFS) is one of the most promising techniques for such purposes due to its outstanding sensitivity and selectivity. 3 Each U(VI) species exhibits a characteristic luminescence spectrum and a corresponding luminescence decay time, allowing spectral deconvolution to get a species distribution from mixed samples. Recently, we demonstrated that U(VI) speciation in a given U(VI) solution of micromolar concentration over a wide pH range can be obtained through a combination of TRLFS and parallel factor analysis (PARAF-AC).…”

“…Uranium content in aquifers is of potential health concern and establishment of an in situ measuring technique is indispensable. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) is one of the most promising techniques for such purposes due to its outstanding sensitivity and selectivity . Each U­(VI) species exhibits a characteristic luminescence spectrum and a corresponding luminescence decay time, allowing spectral deconvolution to get a species distribution from mixed samples.…”