Spectrophotometric determination of cobalt(II) using the chromogenic reagent 4,4'-diazobenzenediazoaminoazobenzene in a micellar surfactant medium

A highly sensitive spectrophotometric method for the determination of cobalt(II) using the chromogenic reagent 4,4'-diazobenzenediazoaaminoazobenzene (BBDAB) was developed, The optimum conditions for the chromogenic reaction of cobalt(II) with BBDAB were studied in the presence of Triton X-100 and sodium tetraborate. The calibration graphs were rectilinear in the range 0-7 mu g per 25 cm(3) cobalt(II). The apparent molar absorptivity is 1.72 x 10(5) dm(3) mol(-1) cm(-1) with a Sandell's sensitivity of 0.00035 mu g cm(-2). The method was applied to the determination of cobalt in soil and vitamin Bit with satisfactory results.