AN UNIDENTIFIED I131CONTAMINANT OF RADIOIODIDE PREPARATIONS12

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Abstract
A non-iodide I131 component was observed in. a number of samples of radioiodide obtained from E. R. Squibb & Sons during the period December 1959 through March 1960. This component, which is referred to as U, for unknown, is both biologically and chemically distinguishable from radioiodide. It resembles closely an I131 component, called Unknown 2, previously encountered in subcellular preparations incubated with radioiodide. U, which appears to be an oxidized form of inorganic iodine, is acid labile and is not as well utilized by thyroid tissue as is radioiodide. Formation of U in radioiodide preparations can be prevented by the presence of reducing agents such as sulfite, cysteine, or 1 methyl-2-mercaptoimidazole. The unknown I131 component was not observed in I131 samples obtained from Oak Ridge National Laboratory, nor was it present in more recent samples of I131 obtained from E. R. Squibb & Sons in which special precautions were taken to prevent its formation.