Iodine is separated from the other radioactive species by extraction into carbon tetrachloride. Before this extraction is made, a complete interchange must be affected between the added iodine carrier and the tracer iodine present in the sample. The carrier iodide (I⁻) is oxidized to periodate (IO₄⁻) in alkaline solution by NaOCl. The IO₄⁻ is reduced to I₂ by hydroxylamine hydrochloride (NH₂OH•HCl) and extracted into CCl₄. The I₂ is back-extracted by reduction to I⁻ with NaHSO₃. Iodide is then precipitated as silver iodide for chemical yield measurement and radioactivity counting.

1. In a 250 mL separatory funnel containing 100 mL water sample (Note 3), add 2 mL of I⁻ carrier solution, 2 mL of NaOH, and 4 mL of NaOCl. Shake funnel for 2 minutes.

2. Add 50 mL of CCl₄, 4 mL of 1M NH₂OH HCl and 3 mL of conc. HNO₃.

3. Shake the funnel for 2 minutes, and allow phases to separate.