Spectrophotometric Determination of Cobalt in Ores with a New Regent 2-(5-Iodine-2-Pyridylazo)-5-Dimethylaminoaniline

High sensitive color reaction of a new reagent of 2-(5-iodine-2-pyridylazo)-5-dimethylaminoaniline(5-I-PADMA) with cobalt(Ⅱ) has been studied.In pH 4.2~9.2 medium,5-I-PADMA reacts with cobalt(Ⅱ) to form a violet-red complex exhibiting two absorption peaks at 554 nm and 602 nm respectively.This complex can be changed into another stable blue-green diproton species after acidification with mineral acids,and the two absorption peaks shift to 568 nm and 614 nm respectively.This species possesses a higher absorption characteristic.The optimal acidification conditions were found to be 0.3~7.0 mol/L HCl,0.3~6.0 mol/L HClO4,0.3~4.2 mol/L H2SO4 and 0.7~7.3 mol/L H3PO4,respectively.The apparent molar absorptivity e614 nm is 1.21×105 L /(mol· cm).Beer′s law is obeyed in the range of 0~0.5 μg/mL for Co.The method provides high sensitivity,high selectivity and less interference.The method has been successfully applied to the determination of cobalt in ores with satisfactory results.