Spectrophotometric determination of cobalt with 2-(2,4-imidazolylazo)-5-dimethylamino-benzoic acid

The synthesis of a new reagent 2-(2,4-imidazolylazo)-5-dimethylamino-benzoic acid(IZD- BA)and its color reaction with Co~(2+) were studied.It was found that the reagent reacted with cobalt (Ⅱ)to form a stable purple complex(2:1 by mole)in the buffer solution of NH_3·H_2O—NH_4Cl at pH 8.0.The maximum absorption wavelength and apparent molar absorptivity were found as 610 nm and 4.15×10~4 L·mol~(-1)·cm~(-1),respectively.Beer's law was obeyed in the range of 0—0.8 mg/L for Co~(2+).The method has been used for the direct determination of cobalt in synthetic waste water with the RSD of 2.2%(n=6) and the recovery of 104.5%(n=6).