SPECTROPHOTOMETRIC DETERMINATION OF TRACE AMOUNTS OF IODIDE BY ITS CATALYTIC EFFECT ON THE CHLORPROMAZINE-HYDROGEN PEROXIDE REACTION

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 (1.0X10(-3) M chlorpromazine, 1.5 M sulfuric acid, 2.0 M hydrogen peroxide, 30-degrees-C), iodide in the range 0.2-10-mu-g 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-mu-g 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.