Sensitive flotation-spectrophotometric determination of niobium with use of oxalate, 3,5-dinitrocatechol and rhodamine B
Résumé
A method of flotation separation with subsequent sensitive spectrophotometric determination of niobium is developed. In the presence of oxalate, niobium and 3,5-dinitrocatechol form an anionic complex able to associate with Rhodamine B (RB). The niobium compound is 'floated' with cyclohexane, dissolved in acetone and the absorbance of the solution is measured at 555 nm. Beer's law is obeyed up to a niobium concentration of 0.3 ?g ml-1; the molar absorptivity is 2.1 x 105 l mol-1 cm-1. The probable composition of the floated compound was established as [(RB+)4][(NbO)2C2O4(DNP)4]4-. In the presence of EDTA the method is fairly selective and becomes specific for niobium after a preliminary extraction of its complex with ?-benzoin oxime from 5 M hydrochloric acid. The method shows good precision and accuracy and was applied to the determination of niobium (1 x 10-5-1 x 10-2%) in geological materials.