Direct spectrophotometric determination of trace cadmium(II) in food samples with 2-acetylmercaptophenyldiazoaminoazobenzene (AMPDAA)

A novel chromogenic reagent, 2-acetylmercaptophenyldiazoaminoazobenzene (AMPDAA), has been prepared by coupling 2-aminoacetylthiophenol to 4-aminoazobenzene through the -NH-N=N-group. In the presence of TritonX-100, AMPDAA reacts with Cd(II) in 1:1 triethanolamine medium to form a red complex with maximum absorption at 529 nm. Under the optimal conditions, Beer's law is obeyed over the range of 0.0 to 1.0 mug mL(-1) Cd(II), and the apparent molar absorptivity is 2.4x10(5) L mol(-1) cm(-1). Based on this, a highly sensitive and selective spectrophotometric method has been developed for direct determination of trace cadmium. The detection limit and the quantification limit were found to be 6.5 and 9.7 mug L-1, respectively. The absorbance of AMPDAA-Cd(II) complex was 0.1881+/-7.5x10(-3) with a 4.9% relative standard deviation for five repeated measurements of the sample containing 2 mug of cadmium in 25 mL solution under the same experimental conditions. Interference of foreign ions was also investigated. Except for Ag(I) and Hg(II), most foreign ions can be tolerated in considerable amounts. Interference caused by Ag(I) and Hg(II) can be reduced by adding sodium thiosulfate. The proposed method has been applied to the determination of trace cadmium in rice, grain and flour samples with satisfactory results.