EXTRACTIVE SPECTROPHOTOMETRIC DETERMINATION OF NIOBIUM(V) WITH 3-HYDROXY-2-(2-THIENYL)-4H-CHROMEN-4-ONE

A coloured complex of niobium (V) with 3-hydroxy-2- (2-thienyl)-4H-chr omen-4-one (HTC) is produced in perchloric acid medium (4 mol/L); it i s quite stable and extractable into dichloromethane. Beer's law is obe yed in the range 0.0-1.9 mu g Nb(V) mL(-1). The molar absorptivity at lambda(max) = 420 nm is 5.0357 x 10(4) L mol(-1) cm(-1). Using Job's m ethod and the mole ratio method, the ratio of metal to ligand (Nb:HTC) in the extracted species has been found to be 1:2. The effect of anio ns and foreign metals is described.