Kinetic spectrophotometric determination of trace iron based on inhibitory of neutral red descoloring

Under the conditions of 80℃ and in sulfuric acid medium,Fe had strong inhibitory action on the colour decolorization of neutral red oxidized by potassium bromate.There was a linear relationship between the amount of Fe and the absorbance difference of the inhibitory reaction system(absorbance A) and un-inhibitory reaction system(absorbance A0) at the wavelength of 520 nm.Based on the fact,a inhibition kinetic spectrophotometry for the determination of trace Fe was established.Under optimal experimental conditions,the linear range of the method was between 0.000 4 μg/mL and 0.064 μg/mL,and the detection limit was 1.41 × 10-4 μg/mL.The kinetic parameters were determined.It was shown that the inhibitory reaction was first-order reaction,the apparent rate constant k was 4.53 × 10-4 s-1 and the apparent activation energy was 69.25 kJ/mol.The method was used for the determination of the trace iron in natural water,with the recoveries of 99.0%-99.5% and the relative standard deviation(RSD) of 3.8%-6.2%.