A kinetic method for the determination of nitrite by its catalytic effect on the oxidation of chlorpromazine with nitric acid

A catalytic spectrophotometric method for the determination of trace amounts of nitrite is proposed. In acidic solution, chlorpromazine (CP) is oxidized by nitric acid to form a red compound, which is further oxidized to a colorless compound. The reaction is accelerated by trace amounts of nitrite and can be followed by measuring the absorbance at 525 nm: nitrite ion is regenerated and multiplied by nitric acid. The absorbance of the reaction increased with an increase in the reaction time, reached a maximum and decreased rapidly. Since the time required for the absorbance to reach the maximum decreased with increasing nitrite concentration, this value was used as the measured parameter for the nitrite determination. Under the optimum experimental conditions (2.3 M nitric acid, 1.2 x 10(-5) M CP, 40 degreesC), nitrite can be determined in the range 0 - 100 mug l(-1). The relative standard deviations (n = 6) are 4.7 and 1.8% for 40 and 100 mug l(-1) nitrite, respectively. The detection limit of this method (3 sigma) is 1.2 mug l(-1). This method was successfully applied to a determination of nitrite in natural water samples.