Unexpected behavior by very small amounts of iodine has been noted by biochemical, medical, and ecological workers. It also has been shown that mild oxidation of carrier-free iodide-131 produced previously unknown species of iodine compounds. It was of interest to determine whether such species also result from the reduction of iodate.
While studying the formation of carrier-free iodate-131 by perchloric acid oxidation of iodide-131 at elevated temperatures, it was found that the acid is not directly responsible for the formation of iodate. Instead, the oxidation is accomplished by a volatile material (thought to be chlorine dioxide) formed only in perchloric acid more concentrated than the hydrate, HClO4·3H2O.
This observation led to the development of a method for generating small amounts of chlorine dioxide for direct use as an oxidant. The gas was applied in a nitrogen gas stream to small volumes of carrier-free iodide-131 solutions during evaporation to dryness at 95°. The residue, redissolved in distilled water, provides a carrier-free iodate-131 solution free of other forms of iodine and macro amounts of other materials.
Studies of the stability of such carrier-free iodate-131 showed that increasing perchloric acid concentrations resulted in increased rate and degree of decomposition; the relative yield of decomposition products (for the most part, "unidentified" species) may also be a function of the acidity. However, with 0.1 M chloride ion in solution, most of the non-iodate activity appeared to be iodide. Reduction of the iodate-131 by dilute sulfite solutions also yielded iodide-131.
Reduction by a 0.005 M ferric/0.05 M ferrous redox couple in 1.0 M perchloric acid led to results predictable from the known chemistry of iodine, provided that the total (carrier) iodate concentration was 10-5 M or greater. In more dilute solutions, at least two "unidentified" species appeared in increased percentages as the carrier iodate concentration was decreased.
Experiments to determine the coprecipitation behavior of carrier-free iodate-131 with silver halides demonstrated only surface adsorption, and only in the presence of excess silver ion. A complete range of carrying behavior was found with the homologous calcium, barium, and lead carbonates. Ferric hydroxide carried 98% of the activity in the pH range 4. 5 to 6.5, whether the precipitate was preformed or formed in the presence of the iodate-131. Silver bromate, and silver and lead periodates, carried the iodate-131 very strongly whether precipitated in the presence of excess anion or cation. Carrier-free iodate-131 was found to have little tendency to form radiocolloids.
A published distillation method for the separation of carrier-free iodine-131 from other materials was known to produce a variety of "unidentified" species of iodine. It was found that the occurrence of these species could be most effectively minimized hy collecting the distillate in solutions of bicarbonate, cysteine hydrochloride, or sulfite.
Inasmuch as numerous workers have used paper chromatographic techniques for analysis of carrier-free iodine-131 solutions, this method was investigated in some detail and found to be unreliable. Large and variable percentages of iodine were lost from the papers during the chromatographic process, and results were frequently at wide variance with data obtained by an established, chemically milder, solvent extraction-isotopic exchange procedure.
Level of Degree
Department of Chemistry and Chemical Biology
First Committee Member (Chair)
Second Committee Member
Raymond N. Castle
Third Committee Member
Guido Herman Daub
Reynolds, Manning S.. "Some Observations on the Chemical Behavior of Carrier-Free Iodine-131 and Dilute Carrier Iodine0127." (1967). https://digitalrepository.unm.edu/chem_etds/152