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 cataly tic effect of iodide on the reaction of triflupromazine (TFP) with H2O2. Th e reaction is followed spectrophotometrically by tracing the oxidation prod uct at 498 nm within 1 min after addition of H2O2. The optimum reaction con ditions are TFP (0.4 x 10(-3) M), H2SO4 (1.0 M), H3PO4 (2.0 M), and H2O2 (1 .6 M) at 30 degreesC. Following this procedure, iodide can be determined wi th a linear calibration graph up to 4.5 ng . cm(-3) and a detection limit o f 0.04 ng . cm(-3), based on the 3 S-b criterion. The method can also be ap plied to the determination of iodate and periodate ions. Determination of a s little as 0.2, 1.0, 2.0, and 4.0 ng . cm(-3) of I-, IO3-, or IO4- in aque ous solutions gave an average recovery of 98% with relative standard deviat ions below 1.6% (n = 5). The method was applied to the determination of iod ide in Nile river water and ground waters as well as in various food sample s after alkaline ashing treatment. The method is compared with other cataly tic spectrophotometric procedures for iodide determination.