title: The surfactant-sensitized analytical reaction of niobium with 8-hydroxyquinoline-5-sulphonic acid.
abstract: Cationic surfactants, such as cetylpyridinium bromide (CPB), sensitize the colour reaction of Nb(V) with 8-hydroxyquinoline-5-sulphonic acid (H(2)L). The formation of a ternary complex of stoichiometry 1:3:3 (Nb-L-CPB) is responsible for the observed enhancement in absorptivity and the quenching in the fluorescence of the Nb-L chelate, when a surfactant is present. The ternary complex exhibits maximum absorption at 383 nm ( = 1.46 +/- 0.01 x 10(4) l.mole(-1).cm(-1)) at pH 5.7, and Beer's law is obeyed up to 6-mug ml Nb concentration. Conditional formation constants of the niobium chelate in the presence and absence of CPB have been determined. On the basis of a detailed spectrophotometric and fluorimetric study the nature of the chromophoric reagent-surfactant interaction and the peculiar features of the sensitization by CPB are discussed.
authors.affiliation: Department of Analytical Chemistry, Faculty of Chemistry, University of Oviedo, Oviedo, Spain.
authors.forename: J I
authors.initials: JI
authors.lastname: Alonso
authors.forename: M E
authors.initials: ME
authors.lastname: Garcia
authors.forename: A S
authors.initials: AS
authors.lastname: Medel