Determination of Organically-bound Iodine in Pharmaceuticals

Abstract

Eight official iodinated compounds with iodine contents from 50 to 66 per cent were assayed by the methods official in U.S.P. XVI and N.F. XI, by reduction with zinc in alkali, and by a standard procedure using oxygen flask combustion. An additional four compounds, formerly official, with iodine content as low as 23 per cent were also examined. The results indicate that the suggested standard procedure is equal or superior to the other methods in recovery of iodine and generally equivalent in reproducibility. The alkaline zinc reduction method is suggested for those compounds having an electronegative substituent ortho or para to the iodine atoms on the aromatic ring. The oxygen flask combustion is suggested for all other iodinated compounds and as a general method. The suggested standard procedure consists of combustion by the oxygen flask method, absorption of the combustion products in an alkaline sulfite solution, and titration of the acidified solution of iodide with standard silver nitrate using a silver-calomel electrode pair for potentiometric determination of the end point.