Kinetic determination of total iodine in urine and foodstuffs using a mixed acid as a pretreatment agent.

An analytical method for the determination of total iodine at the ng level in urine, biological materials and foods was investigated. The organic substances were completely decomposed using a mixed solution of nitric, perchloric and sulfuric acids as pretreatment agents at ca. 230 degrees C. Iodine in the resulting solution was analyzed by a kinetic-photometric method based on the catalytic effect of iodine on the oxidation of chlorpromazine by hydrogen peroxide. The relative standard deviation was 1.6% for 100 ng of iodide and the detection limit of the method was 1.6 ng (3sigma). The proposed method was successfully applied to the determination of iodine at ng levels in real samples.