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

Abstract

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.