Sensitive spectrophotometric determination of vanadium with 2-(5-bromo-2-pyridylazo)-5-diethyl-aminophenol (5-Br-PADAP)

A new sensitive and highly selective method is described for the spectrophotometric determination of microgram amounts of vanadium(V). First, vanadium is isolated by extraction withN-benzoyl-N-phenylhydroxylamine (BPHA) in chloroform from about 4M hydrochloric acid medium. Then, chloroform is evaporated and the residue mineralized with mixture of cone. perchloric and nitric acid. Finally, a colour reaction of vanadium(V) separated with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) in an acetate buffer (pH 4.5) gives a molar absorptivity of 5.48×10⁴l·mol^–1·cm^–1 at 585 nm. The proposed method was applied for the determination of traces of vanadium in aluminium samples. The results obtained show a good precision and accuracy of the method.