Automatic methods for the determination of total inorganic iodine and free iodide in waters

Abstract

Methods for the determination of total inorganic iodine and free iodide, based on the catalytic effect of iodide on the destruction of the thiocyanate ion by the nitrite ion, have been developed and automated. These methods use a Technicon AutoAnalyzer system, and a throughput of 20 samples per hour was achieved. Results obtained for a range of United Kingdom drinking waters showed that the total inorganic iodine method had a coefficient of variation of the order of 3%, a detection limit of 0.2 µg l^–1 of l and a recovery of added iodine of 90–108%. The free iodide method had a coefficient of variation of the order of 10%, a detection limit of 0.4 µg l^–1 of l and a recovery of added iodine of 89–109%. The effects of possible interfering substances on both methods have been investigated and shown to be negligible for normal drinking waters. The stability of dilute iodine solutions stored in containers made of different materials has also been evaluated.