Challenges of uranium determination in biological samples as a nuclear forensics tool

The determination of uranium in biological samples is an essential component of nuclear forensics and internal exposure assessment, yet it remains analytically demanding due to the complex nature of bioassay matrices. Human urine, in particular, contains variable organic constituents and inorganic salts that can severely interfere with radiochemical separation processes and compromise analytical reliability. In this work, the challenges associated with uranium determination in urine samples are critically examined through a detailed investigation of radiochemical separation using U-TEVA® extraction chromatography coupled with alpha spectrometry. Emphasis is placed on identifying matrix-driven effects such as resin fouling, incomplete dissolution, and strong complex formation caused by ammonium urates, oxalates, and residual organic matter. When a conventional separation procedure was applied, uranium recoveries were highly inconsistent and frequently unsuccessful, with chemical yields ranging from 0 to 25.4%. An optimized analytical workflow was therefore developed, incorporating pre-filtration, intensified oxidative digestion, repeated acid treatment, controlled chromatographic conditions, and improved source preparation. The performance of the revised procedure was assessed using a²³²U tracer. Following optimization, uranium recovery increased markedly, achieving values of up to 62.6% and producing well-resolved alpha spectra suitable for quantitative analysis. The findings demonstrate that urine composition plays a decisive role in uranium recovery and that method robustness depends on targeted mitigation of matrix interferences. The proposed approach offers practical guidance for laboratories conducting uranium bioassay measurements and enhances the reliability of analytical results used in nuclear forensic investigations and radiation protection monitoring.