A Kinetic Spectrophotometric Method for the Determination of Trace Copper with Bromophenol Blue and Hydrogen Peroxide

A new catalytic kinetic spectrophotometry for the determination of copper has been established. The method is based on the catalytic effect of trace Cu (Ⅱ) on the oxidizing discoloring reaction of bromophenol blue with hydrogen peroxide using cetyl pyridinium bromide as a sensitizer in HAc-NaAc buffer solution at pH=4.5. Major factors such as acidity, reagent dosage, reaction temperature, reaction time, and the influence of surfactant and coexisting irons were studied. The detection wavelength was selected as 593 nm with optimal conditions. The apparent activation energy of the catalytic reaction was 90.3 kJ/mol. Under the optimal conditions, the detection limit of this method was 6.46×10^-10 g/mL. In the content range of 0 to 0.064 μg/mL, there was a good linear relationship between the concentration of Cu(Ⅱ) and lg(A₀/A). This method was simple, rapid, and highly selective. There were no interferences from the most common coexisting ions during determination. The proposed method was applied to the determination of trace copper in coal. The relative standard deviation was less than 3.1% (n=5), and the recoveries of standard addition were 92.7%-107.0%. The determination reults were consistent with those obtained by atomic absorption spectrometry.