Abstract
Groundwater isotopic screening has gained increased attention for determining the α activity ratio of (234)U/(238)U. This requires efficient uranium preconcentration from aquifer samples and precise measurement of the minor abundant isotope ratio of (234)U/(238)U (approximately 55 ppm). Using polydopamine-coated Fe(3)O(4) magnetic nanoparticles (PDA@Fe(3)O(4)-NPs) to extract uranium from aquifer samples reduces analysis time by over 80% compared to conventional preconcentration methods. Thermal Ionization mass spectrometry (TIMS) with carefully selected detector combinations and a novel methodology was employed to measure the (234)U/(238)U isotope ratio. The methodology involves sequentially collecting the ion current of (235)U on both a Secondary Electron Multiplier and a Faraday cup. Internal normalization using the invariant (238)U/(235)U ratio (∼137.88) is then applied to address isotopic fractionation in the (234)U/(238)U ratio measurements, significantly improving the precision and accuracy to better than 0.1%. Efforts were made to assess all possible sources of uncertainty, identifying the primary contributors so as to strengthen the confidence in the proposed correction methodology and to establish traceability to the SI unit system.