Promises and pitfalls in the reliable determination of 233U using high resolution ICP-OES

Abstract

This study highlights that the currently employed analytical approach for the ICP-OES determination of ²³³U at λ = 385.950 nm is neither specific for this U isotope nor reliable and provides potential solutions for a selective and reliable quantification of ²³³U, ²³⁵U, and ²³⁸U using high resolution ICP-OES. While being a sensitive U wavelength region, the small isotopic line splitting of ²³³U (λ = 385.950 nm), ²³⁵U (λ = 385.955 nm) and ²³⁸U (λ = 385.958 nm) cannot be resolved with any commercial high resolution optical spectrometer. In addition, the width of 5.67 pm of the ²³³U peak, defined as full width at half maximum, is particularly larger than the ²³⁸U peak width of ∼4.3 pm, thus indicating splitting of the ²³³U emission signal into multiple peaks. In contrast, superior U isotopic information can be obtained from isotope specific emission lines centred around λ = 411.6 nm and λ = 424.4 nm with a spectral distance between ²³³U and ²³⁸U of 25 pm and 39 pm, respectively. The ²³³U signal of both wavelength regions, however, suffers from a potential interference with thorium that requires peak deconvolution for accurate quantification of ²³³U.