Flotation-Spectrophotometric Determination of Vanadium with 3,5-Dinitrocatechol and Rhodamine B

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Abstract
International audienceA 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 2.1x105! mol-1 cm-1 at 555 nm and the detection limit is 3ng/ml. Beer's law is obeyed up to a vanadium concentration of 0.3 jig/ml. The composition of the floated compound was established. Its proposed formula is [(RB)j]-[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-/V-phenylhydroxylamine (BPHA) chelate from a HCI-HF medium. The method was applied to the vanadium determination (0.2-9 ppm) in some vegetables. © 1988, The Japan Society for Analytical Chemistry. All rights reserved