A Rapid and Sensitive Method for the Determination of Iodine-131 in Milk by Ion Exchange on Silver Chloride.

Abstract

b Iodine-131, as iodide ion, is separated from other milk constituents by ion exchange on a silver chloride column. After elution as iodic acid from the column by acidified chlorine water, the eluate can b e directly analyzed by gamma counting. The time required to analyze a 1-liter sample by this method is approximately 30 minutes (exclusive of counting time). If beta counting or increased sensitivity is required, the iodine is subjected to two oxidation-reduction solvent-extraction cycles and finally precipitated as silver iodide prior to counting. Chemical and radiochemical yields for both added and metabolized iodide are identical, and are 90 to 95% for homogenized milk and 85 to 95% for raw milk.Total time for the complete procedure (exclusive of counting time) is approximately 2 hours for a single sample. Less than 2 picocuries of total iodine-131 can b e detected in 1 liter of milk, using the complete procedure. The application of the procedure to other materials is discussed.O D I N E -~~~ is an important radio-

Determination of iodine-131 at low concentration in formaldehyde-preserved milk

“…Ion-exchange chromatography (2)(3)(4)(5)(6)(7)(8)(9) is generally employed to isolate 131I from milk. It is found or assumed that 90% of the 131I exists in the iodide form.…”

Ion-exchange chromatography

“…Other inorganic exchangers include zirconium oxalate (281) and chromium tripolyphosphate (39), both selective for cesium ions; antimonio acid (2), which shows an affinity sequence Na > Rb > Cs > K > Li in dilute nitric acid and Na > Cs > Rb > K > Li in ammonium nitrate; manganese dioxide (42) which is selective for manganese and chromium at the tracer level; silver chloride (122), used to absorb traces of iodine-131; stannic phosphate, precipitated in the fibers of paper and used for thin-layer chromatography (287); and the crystalline zeolites, which can be used for column chromatography in molten salt mixtures (77, 78). Different selectivity orders are observed in molten potassium nitrate and lithium nitrate, and an explanation of this difference is suggested (77).…”