AOAC Official Method 2000.04 Iodine-131 in Milk Radiochemical Separation Method First Action 2000

(Applicable to determination of iodine-131 in milk at 0.1-0.3 Bq/L.)
Caution:    This method requires the use of a chlorinated solvent, C(b), a suspected and possible human carcinogen.
See Table 2000.04 for the results of the interlaboratory study supporting acceptance of the method.

A. Principle

The test portion is treated with NaHSO₃ to convert all the iodine to a common (I^-) oxidation state. Iodide is isolated and concentrated on an ion-exchange column. The iodide is oxidized on-column to iodate by NaOCl solution and eluted by this solution. The NaOCl is decomposed and the iodate is reduced by hydroxylamine hydrochloride solution to elemental iodine which is extracted by CC1₄. The iodine is again reduced to iodide and re-extracted into aqueous solution by NaHSO₃ solution. The iodide is coprecipitated with palladium iodide (PdI₂) and the recovery of the carrier is determined gravimetrically. The iodine-131 in the carrier is counted by a beta-gamma coincidence or by a low-background beta counter.