Third-derivative spectrophotometric determination of molybdenum with bromopyrogallol red in the presence of polyvinylpyrrolidone

Abstract

Molybdenum(VI) forms a 1:2 complex with bromopyrogallol red (BPR) in the presence of polyvinylpyrrolidone (PVP) in formic acid-sodium formate buffered solutions (pH 3.80). A simple and highly sensitive method has been developed for the determination of trace amounts of molybdenum by measuring the distance between the peak (λ= 562 nm) and the valley (λ= 628 nm) given by the third derivative of the absorption spectrum of the ternary system Mo^VI-BPR-PVP. The chemical variables (pH, BPR and PVP concentration) and the instrumental variables (scanning range, Δλ and derivative order) were optimised using the modified simplex method. The calibration graph fits the equation d³A/dλ³= 6.6 × 10⁵[Mo]+ 0.06 (r= 0.9998) with a detection limit of 4 p.p.b. and a relative standard deviation of 0.53%. The method has been applied to the determination of molybdenum in pharmaceutical samples.