title: Extraction-spectrophotometric determination of niobium with dibenzo-18-crown-6 and thiocyanate.
abstract: A method is described for the direct spectrophotometric determination of micro-amounts of niobium by extraction into a benzene solution of dibenzo-18-crown-6 (L) from 3M hydrochloric acid containing potassium thiocyanate. The molar absorptivity of the extracted complex is 3.85 +/- 0.03 x 10(4) 1.mole(-1).cm(-1) (relative standard deviation 0.8%). Co-ordinatively unsaturated complexes of the type [NbO(SCN)(3)](2)L and NbO(SCN)(3)L are extracted, along with ion-pairs, especially when small amounts of L are used for extraction. The ion-pair complex [NbOCl(2)(SCN)(3)][(LK)(2)] seems to be the main species formed in the organic phase.
authors.affiliation: Departamento de Química Analítica, Facultad de Ciencias, Universidad de Oviedo, Oviedo, España.
authors.forename: D B
authors.initials: DB
authors.lastname: Gomis
authors.forename: S A
authors.initials: SA
authors.lastname: Jimeno
authors.forename: A
authors.initials: A
authors.lastname: Sanz-Medel