Color Reaction of 2-(4-Chloro-2-phosphophenylazo)-7-(2,4-dichlorophenylazo)-1,8-dihydroxy-3,6-naphthalene sulfonic Acid with Bismuth and Its Application

A sensitive chromogenic reagent,2-(4-chloro-2-phosphophenylazo)-7-(2,4-dichlorophenylazo)-1,8-dihydroxy-3,6-naphthalene disulfonic acid(abbreviation:DC-CPA),has been used in the spectrophotometric determination of bismuth.In 0.06 mol/L HNO3,the reagent reacts with bismuth(Ⅲ) to form a deep color complex with a maximum absorption at 691nm.The apparent molar absorptivity is 1.1×105 L·mol-1·cm-1.Beer's law is obeyed over the bismuth concentration range 0.02~1.4 mg/L.Without interference of foreign ions,the proposed method has been applied to the determination of bismuth in copper alloys with satisfactory results.