Accurate and precise $^{235}$U quantification by combining isotopic dilution method and ICP/AES measurements
Résumé
An ICP/AES owning a high resolving power is able to measure the isotopic shift in emission atomic lines for heavy elements such as uranium. Uranium isotopes, such $^{235}$U and $^{238}$U, are therefore clearly separated and identified. Using this phenomenon, the accurate and precise quantification of uranium or its isotopes is possible. Indeed, the transposition of isotopic dilution mass spectrometry method to our ICP/AES instrument allows to quantify, with trueness and precision, the amount content of $^{235}$U of an uranyl nitrate solution. The method is named IDAES. At our knowledge, this study is the first that combine isotope dilution method and ICP/AES measurements. In order to demonstrate the validity of the IDAES method, an IDMS protocol (the preferred method), using a MC ICP/MS instrument, is also applied to determine the amount content of $^{235}$U of the sample. Both methods led to the same amount content of $^{235}$U for the uranyl nitrate solution (difference between both values is less than 0.1%). As expected, the precision of the IDMS method (less than 1%) is better than the IDAES one (about 3%) but it remains satisfactory. Those results are particularly remarkable since IDAES and IDMS used physically different measuring systems, respectively ICP/AES and MC ICP/MS.
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