Identification of organically bound iodine in soil humic substances by size exclusion chromatography/inductively coupled plasma mass spectrometry (SEC/ICP-MS)

To confirm the existence of iodine bound to soil humic substances such as humic and fulvic acids, a system involving the combination of size exclusion chromatography (SEC) and inductively coupled plasma mass spectrometry (ICP-MS) was employed. A solution extracted from soil with tetramethylammonium hydroxide was applied to the system and the amounts of iodine and humic substances eluted on a molecular weight basis from the column of the SEC were determined by ICP-MS and ultraviolet absorption spectrophotometry, respectively. As a result, besides inorganic iodine (I-, IO3-), iodine contained in organic components with high molecular weights was detected. The iodine contained in the organic components was estimated to be in the organically bound form, because the elution position of iodine was identical with that of the humic substances and the peak height of iodine was proportional to that of the humic substances. The thermal stability of the organically bound iodine was found to be relatively high. In addition, the existence of organically bound bromine was confirmed in humic substances in the same manner as iodine.