Improvements in the Winkler Titration for Iodide in Iodized Salt
Kenneth W. Pratt, Karen E. Murphy
A bromine gas generator, based on bleach, potassium bromide and dilute hydrochloric acid, replaces hazardous pure bromine used in the classical Winkler titration for iodide. This modification eliminates the need to store or use pure bromine. The gas generator transfers a minimal quantity of gaseous bromine to the sample. Nonvolatile impurities that cause an unacceptable drift in the endpoint of the titration remain in the generator solution. The precision of the method is improved by use of boiling to eliminate excess bromine in the titration, buffering the solution pH during the oxidation of iodide to iodate, and using gravimetric titrimetric techniques. Results for iodide spikes in pure sodium chloride yielded a relative expanded uncertainty of 0.18 %. A relative expanded uncertainty of 0.64 % was obtained for iodide in commercial iodized salt samples.