The surfactant-sensitized analytical reaction of niobium with some thiazolylazo compounds

Cationic surfactants, such as cetylpyridinium bromide (CPB), sensitize the color reaction of Nb(V) with 1-(2-benzothiazolylazo)-2-hydroxy-3-naphthoic acid (I-a), 5-(benzothiazolylazo)2,5-naphthalenediol (I-b), 5-(2benzothiazo lylazo)8-hydroxyquinoline (I-c) and 4-(2- benzothiazolylazo)2,2-biphenyldio l (I-d) reagents. The formation of a ternary complex of stoichiometric rati o 1:2:2 (Nb-R-CPB) is responsible for the observed enhancement in the molar absorptivity and the Sandell sensitivity of the formed complex, when a sur factant is present. The ternary complex exhibits absorption maxima at 649, 692, 661 and 612 nm, (epsilon = 3.35 x 10(4), 3.59 X 10(4), 4.46 X 10(4) an d 2.79 x 10(4) 1 mol(-1) cm(-1))on using reagent I-a, I-b, I-c, and I-d, re spectively. Beer's law is obeyed between 0.05 and 2.50 mug ml(-1) while app lying the Ringbom method for more accurate results is in the range from 0.2 0 to 2.30 mug ml(-1) Conditional formation constants in the presence and ab sence of CPB for niobium complexes have been calculated. On the basis of a detailed spectrophotometric study, the nature of the chromophoric reagent-s urfactant interaction and the peculiar features of the sensitization by CPB are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.