A new sensitive catalytic method for the determination of copper (II) is proposed. In the presence of hydrogen peroxide, copper (II) catalyzes the oxidation of p- hydrazinobenzenesulfonic acid to p-sulfobenzenediazonium ion, which is coupled with m- phenylenediamine to form a yellow azo dye (λ max= 454 nm). By means of this catalytic reaction, nanogram amounts of copper (II) can be determined easily.
