Spectrophotometric determination of cobalt in zinc-cobalt alloy plating solution with dibromomethyl carboxyazo

The chromogenic reaction between the reagent dibromomethyl carboxyazo and cobalt was studied. In an ammonium citrate and ammonia solution with pH 10,cobalt reacts with the reagent to form a blue complex which exhibits an absorption maximum at 660 nm with a apparent molar absorptivity of 1.77 × 104 L/(mol·cm). Beer’s law was obeyed in the range of 0-80 μg/(25 mL) for cobalt. The proposed method has been applied to direct determination of cobalt in zinc–cobalt alloy plating solution with RSD between 1.4% and 1.9% and recovery between 98% and 102%.