Extraction and spectrophotometric determination of molybdenum(VI) with N-phenylbenzohydroxamic acid and phenylfluorone

Abstract

N-Phenylbenzohydroxamic acid reacts with molybdenum(VI) in 3.5–6.0 M hydrochloric acid to give a complex that is extractable into chloroform. The chloroform extract of the molybdenum complex, on second extraction from a dilute hydrochloric acid medium (0.2–0.3 M) in the presence of phenylfluorone and ethanol, forms an intensely coloured complex possessing an absorption maximum at 518 nm. Job's method of continuous variation reveals that the complex is Mo(VI)—2NPBHA—PF. The molar absorptivity under optimum conditions is 7.4 × 104 cm3 mol−1 cm−1. The system obeys Beer's law up to 0.6 ppm of molybdenum(VI). Considerable amounts of many cations and anions can be tolerated. The interference from vanadium(IV) and vanadium(V) can be eliminated by the addition of sodium metabisulphite, whereas the interference from titanium(IV) is mitigated by oxalate ions. The method has been successfully applied for the determination of molybdenum in a standard steel sample.