Spectrophotometric determination of cadmium with о-methylbenzenediazoaminoazobenzene

A spectrophotometric method for the determination of cadmium(Ⅱ) is described.The method is based on the color reaction between cadmium and a new chromogenic reagent о-methylbenzenediazoaminoazobenzene(о-MDAA).о-MDAA reacts with Cd(Ⅱ) to give a reddish complex with molar ratio of 2∶1(R∶Cd) in the 0.08 mol/L ammonia solution and in the presence of non-ionic surfactant TritonX-100.The maximum absorption wavelength of the complex is at 524 nm.Beer's law is obeyed in the concentration range of 0 to 5 μg for Cd(Ⅱ) in 25 mL solution and the apparent molar absorptivity is found to be 1.68×105 L·mol-1·cm-1.Selectivity of this method is improved by the addition of sodium citrate,and the color reaction isn't affected by a great deal of copper(Ⅱ) existed.The proposed method has been successfully applied to the determination of cadmium in copper alloy and pure copper samples,giving relative standard deviation(RSD) from 1.02% to 2.31%.