Spectrophotometric Determination of Trace Amounts of Iodide by Its Catalytic Effect on the Chlorpromazine-Hydrogen Peroxide Reaction

Abstract

A catalytic photometric method for the determination of trace amounts of iodide is proposed. In the presence of iodide, chlorpromazine is oxidized by hydrogen peroxide in a sulfuric acid solution to form a red intermediate, which is further oxidized to a colorless compound. The reaction is followed by measuring the increase in the absorbance at 525 nm; the maximum absorbance is obtained on an absorbance-time curve at a given reaction time. Since the maximum value increases with an increase in the iodide concentration, this value is used as a parameter for the iodide determination. Under the optimum experimental conditions (1.0×10^-3 M chlorpromazine, 1.5 M sulfuric acid, 2.0 M hydrogen peroxide, 30°C), iodide in the range 0.2–10 (µg l⁻¹ can be determined. The relative standard deviations are 0.8, 2.6 and 4.2% for 6.0, 2.0 and 0.6 (µg l⁻¹ iodide, respectively. Although iodate shows the same catalytic effect as iodide at the same concentration as iodine, free iodine shows a somewhat lower catalytic effect. The procedure has been applied to the determination of iodide in natural water samples.