Abstract: A new spectrophotometric method for determining trace potassium bromate in wheat flour based on oxidation-decoloration of butyl rhodamine B (BRB) was established. The effects of some important factors such as acidity, concentration and volume of BRB, reaction time and reaction temperature were investigated to acquire the optimal conditions. The results indicated that the optimal conditions were maximum absorption peak at 558 nm, 0.3 mol/L hydrochloric acid and 1.0 mL 1.00 × 10-4 mol/L BRB solution, reaction temperature of 80 ℃ and reaction time of 5 min. Beer's law was obeyed in the range of 0 to 0.3μg/mL for potassium bromate. The regression equation was δA = 1.607C + 0.0057 (C: μg/mL) with a correlation coefficient of 0.9996. The detection limit was 0.08μg/g with a molar absorption coefficient of 1.6×106 L/(mol ·cm). The developed method was used for the determination of trace potassium bromate in wheat flour with satisfactory results. The recovery rate of samples was in the range of 92%－109% with relative standard deviation of less than 5%.

Key words: butyl rhodamine B, spectrophotometric method, potassium bromate, wheat flour