Pneumatoamperometric Determination of Nanogram Amounts of Cyanide

Part-per-billion levels of cyanide react rapidly and quantitatively with excess iodine at pH ~6.0 to form iodine cyanide. The excess iodine is selectively removed from solution by nitrogen purging. Acidification of the resultant iodine cyanide solution with perchloric acid in the presence of iodide to a final concentration of 3.0 M HCl0₄ and 1.0 X 10^-4M I^-rapidly and quantitatively regenerates iodine in an amount equivalent to the original cyanide. This iodine is transferred to the gas phase by purging with nitrogen, where it is determined at a gold gas porous electrode by electro-oxidation to lodate. The detection limit for cyanide is estimated to be 5 ng in a 4-mL sample.