Analytical Sciences

Flow Injection Spectrophotometric Catalytic Determination of Iodine in Milk

Ana Rita de Araujo NOGUEIRA * , Fabiana MOCKIUTI, Gilberto Batista de SOUZA and Odo PRIMAVESI

Empresa Brasileira de Pesquisa Agropecuária-Pecuária Sudeste, P. O. Box 339, S. Carlos SP, 13560-970, Brazil

A flow injection method based on the catalytic action of iodide on the color-fading reaction of the FeSCN 2+ complex was proposed and applied to the determination of iodine in milk. At pH 5.0, temperature 32ûÃ and measurements at 460 nm, the decrease in absorbancy of Fe 3+ -SCN (0.10 and 0.0020 mol l -1 ) in the presence of NO2 - (0.3 mol l -1 ) is proportional to the concentration of iodide, with linear response up to 100.0 mg I - l -1 . The detection limit was determined as 0.99 mg I - l -1 (3 s blank/slope); and the system handles 48 samples h -1 . Organic matter was destroyed by a dry procedure carried out under alkaline conditions. Alternatively, the use of a Schöninger combustion after the milk dehydration was evaluated. The residue was taken up in 0.12 mol l -1 KOH solubilization. For typical samples, recoveries varied from 94.5 to 105%, based on the amounts of both organic matter destroyed. The accuracy of the method was established by using a certified reference material (IAEA A-11, milk powder) and a manual method. The proposed flow injection method is now applied as an indicator of milk quality in a Brazilian milk production system. (Keywords: Iodine, flow injection system, catalytic action, milk, spectrophotometry)

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