A thermo extraction-UV/Vis spectrophotometric method for total iodine quantification in soils and sediments.
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%.
Gilfedder
B S
BS
Institut für Umweltgeochemie, Neuenheimer Feld 236, 69120, Heidelberg, Germany. benjamin.gilfedder@ugc.uni-heidelberg.de
Althoff
F
F
Petri
M
M
Biester
H
H
D019015:Geologic Sediments / Q000737:chemistry*; D006358:Hot Temperature; D007455:Iodine / Q000032:analysis* / Q000737:chemistry; D010084:Oxidation-Reduction; D012015:Reference Standards; D015203:Reproducibility of Results; D012989:Soil Pollutants / Q000737:chemistry*; D013053:Spectrophotometry / Q000379:methods*
D012989:Soil Pollutants; D007455:Iodine