Flow Injection Spectrophotometr ic Catalytic Determination of Iodine in Milk.

Abstract

A flow injection method based on the catalytic action of iodide on the color-fading reaction of the FeSCN2+ complex was proposed and applied to the determination of iodine in milk. At pH 5.0, temperature 32°C and measurements at 460 nm, the decrease in absorbancy of Fe3+-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 μg I- l-1. The detection limit was determined as 0.99 μg I- l-1 (3σ 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 Schoninger 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.