Kinetic spectrophotometric determination of trace cadmium based on its inhibitory effect on discoloring reaction of xylenol orange and peroxide hydrogen

A kinetic spectrophotometric method for the determination of trace cadmium(Ⅱ) based on its inhibitory effect on discoloring reaction of xylenol orange(XO) with peroxide hydrogen in the buffer solution of Na2B4O7-NaOH is described.The influence of the factors such as acidity,concentration of reactants,reaction time,temperature and co-existing ions on the reaction is discussed.The optimum conditions of reaction are established and some kinetic parameters are determined.The maximum absorption wavelength of the product is at 580 nm.The linear range of determination is 0.6-1.6 μg/mL and the detection limit of the method is 0.15 μg/mL.Foreign ions hardly interfere in the determination.The interferences from Co2+,Cu2+,Fe3+,Mn2+ ions were eliminated by triethanolamine and β-mercaptopropionic acid.The apparent activation energy of catalytic reaction is 58.27 kJ/mol.The method had been successfully applied to the determination of trace cadmium in rock,with the relative standard deviations(RSD)of 2.4%-3.0%,and the recoveries of between 95%-103%.