Abstract
Iodine in soils and sediments is a difficult element to analyze due to its volatility in acidic conditions. Traditionally it has been quantified using neutron activation analysis techniques, which, unfortunately, requires access to a nuclear reactor. We present here a simple method for solid-phase iodine analysis by thermo extraction at 1000°C and quantification by UV/Vis photometry. Samples are combusted in an oxygen stream and trapped in Milli-Q water. The extracts are then quantified by an As3+–Ce4+ spectrometric method whereby iodide catalyzes the oxidation of As3+ to As5+ and reduction of Ce4+ to Ce3+. Three standard reference materials were analyzed with excellent recoveries (97–113%) and RSDs (<5%). Moreover, the detection limit was less than 50 ng absolute iodine with a confidence limit of 95%. When applied to carbonate-rich samples from sediment traps deployed in Lake Constance we found very low iodine levels (0.8–2 mg kg−1). Despite the low concentrations, the precision of the method was consistently better than 5% RSD. However, the method needed to be slightly modified for organic and iodine-rich sediments (20–30% organic carbon) from a lake in the Black Forest by increasing the oxygen flow rate and decreasing the combustion time. Using the modified method we were able to achieve RSDs lower than 5%.
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Acknowledgements
We would like to thank Dr M. Wessels from the Langenargen Lake Research Institute for the Lake Constance sediment trap samples. Two reviewers also contributed to improving the manuscript. This project was funded by the Deutsche Forschungsgemeinschaft to H. Biester under contract No. BI-734/4-5.
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Gilfedder, B.S., Althoff, F., Petri, M. et al. A thermo extraction–UV/Vis spectrophotometric method for total iodine quantification in soils and sediments. Anal Bioanal Chem 389, 2323–2329 (2007). https://doi.org/10.1007/s00216-007-1621-4
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DOI: https://doi.org/10.1007/s00216-007-1621-4