CATALYTIC DETERMINATION OF IODIDE BY A MAXIMUM ABSORBENCY METHOD USING THE OXIDATION REACTION OF CHLORPROMAZINE WITH HYDROGEN-PEROXIDE

Chlorpromazine is oxidized catalytically in the presence of iodide wit h 1 M hydrogen peroxide in 1 M sulphuric acid medium to form a red rad ical, which is further oxidized to a colourless sulphoxide. The plot o f absorbance at 528 nm vs. reaction time shows an absorbance maximum p roportional to the concentration of iodide ions in the range 0-7 ng ml - 1. The method has the advantage that careful control of the reactio n time and temperature is not needed; the reaction temperature has lit tle influence on the determination in the range 20-40-degrees-C. The m ethod also gives a higher sensitivity and shows less influence of the concentrations of hydrogen peroxide and sulphuric acid than the tangen t method using the initial reaction. The limit of detection is about 0 .1 ng ml -1 (0.5 ng in 5 ml of measured solution). The effects of fore ign ions were investigated. The mechanism of the reaction is discussed .