The spectrophotometric and derivative spectrophotometric determination of cobalt in the presence of large amounts of nickel using Br-PADAP

The present work describes the use of 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP) as the spectrophotometric reagent for cobalt determination in nickel and its matrices. Br-PADAP reacts with cobalt(II) forming a red complex with absorption maxima at 589 and 567 nm. The following parameters were studied: complex stability, pH effect, amount of Br-PADAP, amount of acetate buffer, EDTA effect, order of the addition of reagents, and obedience to Beer's Law. The results demonstrated that Br-PADAP can be used for cobalt determination in the presence of large amounts of nickel, at pH 4.0, with a molar absorptivity of 8.30 x 10(4) L/mol/cm (at 589 nm). Beer's Law is obeyed for at least 0.80 mu g/mL. Br-PADAP also reacts with nickel, but the complex formed completely decomposes after addition of EDTA. The proposed procedure was used for cobalt determination in several nickel matrices. The results obtained for cobalt by the Br-PADAP method and the ICP method were statistically compared by means of the Student t-test and the variance ratio F-test, and no significant difference was found.