A highly sensitive color reaction of cadmium and the action mechanism of surfactants were studied by using 2-chloro-4-nitrobenzenediazoaminoazobenzene (CNDAA) as chromogenic reagent. It was shown that Cd(II)-CNDAA complex could be solubilized and sensitized by nonionic surfactants, anionic surfactants and nonionic-anionic mixed surfactants. Four new methods for spectrophotometric determination of trace cadmium were built based on the system of Cd(II)-CNDAA-SF. The proposed method has a high sensitivity, good selectivity and a wide acidity range of color reaction and were used for determination of trace cadmium in aluminum alloy with satisfactory results. Moreover, the structure of Cd(II)-CNDAA complex was investigated. The relationship between the dissociation constant of reagent (pKa), acidity of color reaction, and the selectivity of method were also described.

Key words: SURFACTANTS, CADMIUM, COLOR REACTION, COMPLEX REACTION