Extractive Spectrophotometric Determination of Niobium (V) Using 3- Hydroxy-2-(4’-Methoxyphenyl)-4-Oxo-4H-l-Benzopyran as a Complexing Agent

3-Hydroxy-2-(4’-methoxyphenyl)-4-oxo-4H-l-benzopyran (HMPB) forms a yellow colored (1:3) complex with niobium (V), which is extracted into dichloromethane from 1.04–4.40 molL -1 HClO4 solution showing an absorption maximum at 398 – 412 nm (figure curve A: 1.0 μg Nb ml -1 versus blank; curve B: blank versus DCM) with Beer's law range of 0–1.3 μg Nb ml -1 , molar absorptivity of 3.764 10 4 L mol -1 cm -1 and the detection limit as 0.036 μg ml -1 . The results are highly reproducible with a standard deviation of ± 0.0037. The linear regression equation is Y=0.399X + 0.006 and the correlation coefficient, r = 1.0004 The method is free from the interference of a large number of analytically important elements. The proposed method handles satisfactorily the analysis of several samples of varying complexity.