Kinetic Determination of Iodide Based on its Effect on the Hydrogen Peroxide Oxidation of Triflupromazine

 A new selective, sensitive, and simple kinetic method is developed for the determination of trace amounts of iodide. The method is based on the catalytic effect of iodide on the reaction of triflupromazine (TFP) with H2O2. The reaction is followed spectrophotometrically by tracing the oxidation product at 498 nm within 1 min after addition of H2O2. The optimum reaction conditions are TFP (0.4 × 10−3M), H2SO4 (1.0M), H3PO4 (2.0M), and H2O2 (1.6M) at 30°C. Following this procedure, iodide can be determined with a linear calibration graph up to 4.5 ng ċ cm−3 and a detection limit of 0.04 ng ċ cm−3, based on the 3 Sb criterion. The method can also be applied to the determination of iodate and periodate ions. Determination of as little as 0.2, 1.0, 2.0, and 4.0 ng ċ cm−3 of I−, IO3-, or IO4- in aqueous solutions gave an average recovery of 98% with relative standard deviations below 1.6% (n = 5). The method was applied to the determination of iodide in Nile river water and ground waters as well as in various food samples after alkaline ashing treatment. The method is compared with other catalytic spectrophotometric procedures for iodide determination.