Rapid and efficient autoclave digestion for the extraction of iodine-129 from urine samples

A new method was developed to extract ¹²⁹I from urine samples and measure it using accelerator mass spectrometry (AMS). The samples were pre-treated in an autoclave with hydrogen peroxide and were then acidified with nitric acid, followed by the precipitation of iodine as silver iodide (AgI) for measurement by AMS. This new procedure is substantially faster than previous methods for the extraction of iodine from urine and results in less chemical waste. The efficiency and reproducibility of this method were evaluated by using ¹²⁵I as a yield tracer, eventually giving a recovery above 99%. To achieve this, several iterations of the method were required. The method was then successfully applied to measure ¹²⁹I/¹²⁷I isotopic ratios and ¹²⁹I concentrations in 25 human urine samples. The AMS results for ¹²⁹I in urine ranged 3.3 × 10⁶ atoms/L to 884 × 10⁶ atoms/L and the isotope ratio (¹²⁹I/¹²⁷I) in human urine ranged from 7.38 × 10^-12 to 3.97 × 10^-10 with a median of 1.29 × 10^-10. This new method will be useful for investigations into the sources of iodine in the human diet and their relative importance for iodine sufficiency.