In order to establish the relationship between the structure of triazene reagent and its analytical properties, twenty-nine triazene reagents have been designed and synthesized. In the presence of nonionic surfactants TritonX-, the colour reaction of the reagents with cadmium (II) and the acid dissociation constant of reagents have been studied. The results show that (1) the Hammett's equation is obeyed in the acid dissociation constant of the reagents and reaction constant ρ is equal to 2.23; (2) an empirical formula, pH～optimum=pKa-(1.70±0.20) is obtained, where pKa is acid dissociation constant of the triazene reagent and pHoptimum is the optimum acidity of colour reaction of the reagent with cadmium(II).

Key words: INFRARED SPECTROPHOTOMETRY, CADMIUM, COLOR REACTION, STRUCTURE AND PROPERTY CORRELATION