Spectrophotometric determination of vanadium(IV) in the presence of vanadium(V) using Br-PADAP

Abstract

In the present paper, a simple and sensitive method is proposed for vanadium(IV) determination in the presence of vanadium(V). This is based on the oxidation of vanadium(IV) present in the sample to vanadium(V) by addition of iron(III) cation, followed by a complexation reaction of iron(II) with the spectrophotometric reagent 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP). The iron(II) reacts with Br-PADAP immediately, forming a stable complex with a large molar absorptivity. The vanadium(IV) determination is possible, with a calibration sensitivity of 0.549 μg ml−1, for an analytical curve of 18.8 ng ml−1 to 2.40 μg ml−1, molar absorptivity of 2.80 × 104 1 mole−1 cm−1 and a detection limit of 5.5 ng ml−1. Selectivity was increased with the use of EDTA as a masking agent. The proposed method was applied for the vanadium(IV) determination in the presence of several amounts of vanadium(V). The results revealed that 200 μg of vanadium(V) do not interfere with determination of 5.00 μg of vanadium(IV). The precision and the accuracy obtained were satisfactory (R. S. D.<2%).