Microdetermination of vanadium in environmental samples as its ternary complex with N-p-aminophenyl-2-thenylacrylohydroxamic acid and 3-(o-carboxyphenyl)-1-phenyltriazine-N-oxide

Abstract

Eleven hydroxamic acids together with a phenyltriazine derivative have been investigated for possible use in the extractive separation and spectrophotometric determination of vanadium(V). From the results of this investigation a method is described for the highly sensitive, selective and rapid determination of vanadium(V) at sub-microgram levels in alloy steels, minerals, animal and plant tissues and natural waters. Vanadium(V) is selectively extracted from a strongly acidic (3.5–7.5 M HCl) medium with a solution of N-p-aminophenyl-2-thenylacrylohydroxamic acid (ATHA) in chloroform. The reddish violet extract (molar absorptivity 9.1 × 10³ l mol^–1 cm^–1 at λ_max.= 550 nm) is then equilibrated with 3-(o-carboxyphenyl)-1-phenyltriazine-N-oxide at about pH 1.5. The resulting ternary complex is more highly coloured (molar absorptivity 1.55 × 10⁴ l mol^–1 cm^–1 at λ_max.= 455 nm) and obeys Beer's law at 455 nm over the range 0.2–15 µg ml^–1 of vanadium(V). The extraction system enables a 25-fold enrichment of vanadium(V) to be achieved and allows the determination of the metal down to p.p.b. (ng l^–1) levels. The proposed method tolerates the presence of a large number of anions and cations that are normally found with vanadium in alloys, rocks, plant and animal tissues and natural waters. The applicability of the method was tested by the determination of vanadium in these matrices; ATHA was selected from 11 hydroxamic acids as it provided the maximum sensitivity and selectivity.