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

A catalytic photometric method for the determination of trace amounts of iron is proposed. In the presence of iron (Fe-II and Fe-III), chlorpromazine is oxidized by hydrogen peroxide in a hydrochloric acid solution to form a red intermediate, which is further oxidized to a colorless compound. The reaction is followed by measuring an increase in the absorbance at 525 nm; the absorbance/time curve increased with the increase in the reaction time, and reaches a maximum value. Since the slope of the linear range of absorbance/time curves increases with the increase in the iron concentration, tan alpha [=Delta(abs.)/Delta(sec.)] is used as a parameter for the iron determination. Under the optimum experimental conditions (0.011 M chlorpromazine, 0.43 M hydrochloric acid, 0.12 M hydrogen peroxide, 30 degrees C), iron can be determined in the range 5 - 200 mu g l(-1). The relative standard deviations are 0.8, 2.3 and 6.6% for 80, 40 and 10 mu g l(-1), respectively. Under the reaction conditions, W-VI, S2O32-, IO3-, I-, NO2- and BrO3- showed interference at concentrations of 1 mg l(-1). These ions showed no interference at concentrations one order lower. The procedure has been applied to the determination of iron in tap and natural fresh water samples.