A Novel Approach for the Simultaneous Determination of Iodide, Iodate and Organo-Iodide for I-127 and I-129 in Environmental Samples Using Gas Chromatography-Mass Spectrometry

In aquatic environments, iodine minty exists as iodide, iodate, and organic iodine. The high mobility of iodine in aquatic systems has led to I-129 contamination problems at sites where nuclear fuel has been reprocessed, such as the F-area of Savannah River Site. In order to assess the distribution of I-129 and stable I-127 in environmenta systems, a sensitive and rapid method was developed which enables determination of isotopic ratios of speciated iodine. Iodide concentrations were quantified using gas chromatography-mass spectrometry (GC-MS) after derivatization to 4-iodo-N,N-dimethylaniline. Iodate concentrations were quantified by measuring the difference of iodide concentrations in the solution before and after reduction by Na2S2O5. Total iodine, including inorganic and organic iodine, was determined after conversion to iodate by combustion at 900 degrees C. Organo-iodine was calculated as the difference between the total iodine and total inorganic iodine (iodide and iodate). The detection limits of iodide-127 and iodate-127 were 0.34 nM and 1.11 nM, respectively, whereas the detection limits for both iodide-129 and iodate-129 was 0.08 nM (i.e., 2pCi I-129/L). This method was successfully applied to water samples from the contamineted Savannah River Site, South Carolina, and more pristine Galveston Bay, Texas.