PNNL

Abstract

129I is a contaminant of interest in the vadose zone and groundwater at numerous federal and privately-owned facilities. Several techniques have been utilized to extract iodine from solid matrices; however, all of them rely on two fundamental approaches: liquid extraction or chemical/heat facilitated volatilization. While these methods are typically chosen for their ease of implementation, they do not totally dissolve the solid. Because some of the iodine partitions onto the soil, extraction methods that do not result in total sample dissolution could underestimate the total iodine content of solid samples. We defined a method that produces complete solid dissolution and conducted laboratory tests to assess its efficacy to completely extract iodine from solid matrices. Testing consisted of potassium nitrate/potassium hydroxide fusion of the sample, followed by sample dissolution in a mixture of sulfuric acid and sodium bisulfite. Direct analysis of the dissolved sample was performed via inductively coupled plasma mass spectrometry (Perkin Elmer Elan DRC II) using a tertiary amine (Spectrasol CFA-C) carrier solution. The fusion extraction method resulted in complete sample dissolution of all solid matrices tested: sediment, glass samples containing low-levels of iodine, as well as tank waste material collected from the Hanford Site. Quantitative analysis of iodine (127I and 129I) showed better than ± 10% accuracy for certified reference standards, with the linear operating range extending more than three orders of magnitude (0.005 to 5 ug/L). Extraction and analysis of four replicates of standard reference material (San Joaquin Soil) from the National Institute of Standards and Technology, Gaithersburg, MD, resulted in an average recovery of 98% with a relative percent deviation of 6%. This simple and cost-effective technique can be applied to solid samples of varying matrices with little or no adaptation.