A thermo extraction–UV/Vis spectrophotometric method for total iodine quantification in soils and sediments

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 degrees 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%.

An iodine mass-balance for Lake Constance, Germany: Insights into iodine speciation changes and fluxes

“…The sediment was freeze dried and milled (in a ball mill) at the Institute for Lake Research, Langenargen. Total iodine concentrations in the sediments were analysed by the TESI (Thermal Extraction with vis-Spectrometry for total Iodine) method as described by Gilfedder et al (2007a). Briefly, this method involves burning the samples at 1000°C in an oxygen stream and trapping the volatilised iodine in distilled water.…”

Reference Materials in Geoanalytical and Environmental Research ‐ Review for 2006 and 2007

“…Mainly, it has been quantified using NA A. Gilfedder (2007) used the soil RMs NCS DC 73321 (Chinese soil) and NIST SRM 2711 with certified I concentrations to test the recovery, accuracy, precision and reproducibility of their simple thermo extraction -UV/Vis spectrophotometric method. PPS-46 is an inorganic soil RM from Environmental Resource Associates (ERA).…”

Iodine speciation and cycling in limnic systems: observations from a humic rich headwater lake (Mummelsee)

“…The porewater accounted for less than 0.5% of the total iodine. After pore water extraction the remaining sediment was freeze dried, milled in an agate ball mill and then analysed for total iodine concentrations as 5 given in Gilfedder et al (2007a). Briefly, each dried and milled sediment sample (20-50 mg) is placed in the quartz tube of an AOX machine and combusted in an oxygen stream at 1000 • C. The released iodine vapour is then trapped in a connecting bubbler (formerly the sulfuric acid bubbler of the AOX) by Milli-Q water.…”