Abstract
A new method of flotation separation and preconcentration of vanadium traces is described. The ion-associate formed by the anionic vanadium(V)-3, 5-dinitrocatechol complex and Rhodamine B is floated with cyclohexane. The separated and washed compound readily dissolves in acetone, giving an intensely coloured solution which forms the basis for a sensitive spectrophotometric determination of vanadium. The molar absorptivity is 2.1×105l mol-1 cm-1 at 555nm and the detection limit is 3ng/ml. Beer′s law is obeyed up to a vanadium concentration of 0.3μg/ml. The composition of the floated compound was established. Its proposed formula is [(RB)2]- [VO(OH)(DNC)2]. EDTA, oxalate and some metals interfere. The method becomes specific for vanadium after a preliminary extraction of the metal as its N-benzoyl-N-phenylhydroxylamine (BPHA) chelate from a HCl-HF medium. The method was applied to the vanadium determination (0.2-9ppm) in some vegetables.
