Extractive spectrophotometric determination of niobium(V) using 3-hydroxyflavone

A simple, rapid method for the spectrophotometric determination of niobium in trace amounts is presented, employing 3-hydroxyflavone as a ligand for the complexation of the metal ion and extracting the coloured complex into chloroform from 4M HClO₄ solution. Beer's law is obeyed in the range 0.0 to 3.2 g ml^–1 Nb(V), with a lower working limit of 0.1 g ml^–1 Nb(V). Molar absorptivity and Sandell's sensitivity of the complex at 395 nm are 4.088 × 10⁴l mol^–1 cm^–1 and 0.002g Nb(V) cm^–2, respectively. The stoichiometry of the complex is established as 12 by Job's and mole ratio methods. The method is free from the interference of a large number of analytically important elements. The proposed system handles satisfactorily the analysis of several samples of varying complexity. The results are highly reproducible with a relative standard deviation of 0.34% for 20 g of Nb.