Determination of trace titanium (IV) by kinetic spectrophotometry based on the inhibitory fading reaction of bromophenol blue

Trace titanium (IV) had significant inhibitory action on the fading reaction of bromophenol blue oxidized by potassium periodate in hydrochloric acid medium at 90°C. Moreover, the absorbance difference (ΔA) between inhibitory reaction and non-inhibitory reaction showed good linear relationship with the mass concentration (ρ) of titanium (IV) in range of 0.6-2.0 μg/mL at 599 nm. On the basis of this phenomenon, a new determination method of trace titanium (IV) by inhibitory kinetic spectrophotometry was established. The detection limit of this method was 7.87×10 ^-10 g/mL. The standard solution of titanium (IV) (0.04 μg /mL) was determined for 12 times with standard deviation of 1.2%. The kinetic parameters were measured. The results showed that this catalytic reaction was first order reaction for titanium (IV), and the total reaction was pseudo first order reaction. The apparent reaction rate constant was 5.85×10 ^-4/s, and the apparent activation energy was 45.42 kJ/mol. The proposed method was applied to the determination of titanium (IV) in two steelmaking sinter samples with different contents of titanium. The determination results were consistent with the reference values. The relative standard deviations (RSD, n=6) were 2.4% and 2.0%, respectively. The recoveries of standard addition were in the range of 98%-101%, which could meet the analytical requirements of trace elements.