Synthesis of a new reagent 5-(5-iodine-2-pyridylazo)-2,4-diaminotoluene and its color reaction with cobalt

5-(5-Iodine-2-pyridylazo)-2,4-diaminotoluene(5-I-PADAT)as a new chromogenic reagent was synthesized and its color reaction with cobalt was also investigated.In a pH range of 3.6～10.0,5-I-PADAT reacted with Co(Ⅱ)to form a stable complex exhibiting two absorption peaks at 521 nm and 571.5 nm,respectively.In a medium containing 0.6～3.0 mol/L HClO4,the complex could be transformed into another species,and the two absorption peaks shifted to 532 nm and 580 nm,respectively.The apparent molar absorptivity was 1.24×105 L·mol-1·cm-1 at 580 nm.The Beer's law was obeyed in the range of 0～400 μg/L.This method has high sensitivity and selectivity.It has been successfully applied to the determination of trace cobalt in VB12 ampoule and ore with satisfactory results.