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

摘要

Cationic surfactants,such as cetylpyridinium bromide (CPB),sensitize the color reaction of Nb(IV) with 1-(2-benzothiazolylazo)-2-hydroxy-3-naphthoic acid(I_a),5-(benzothiazolylazo)2,5-naphthalenediol (I_b),5-(2-benzothiazolylazo)8-hydroxyquinoline (I_c) and 4-(2-benzothiazolylazo)2,2-biphenyldiol(I_d) reagents.The formation of a ternary complex of stoichiometric ratio 1:2:2 (Nb-R-CPB) is responsible for the observed enhancement in the molar absroptivity and the Sandell sensitivity of the formed complex,when a surfactant is present.The ternary complex exhibits absorption maxima at 649,692,661and 612 nm(#epsilon#=3.35*10~4,3.59*10~4,4.46*10~4 and 2.79*10~4 l mol~(-1) cm~(-1) on using reagent I_a,I_b,I_c,respectively.Beer's law is obeyed between 0.05 and 2.50 #mu#g ml~(-1),while applying the Ringbom method for more accurate results is in the range from 0.20 to 2.30 #mu#g ml~(-1).Conditional formation constats inthe presence and absence of CPB for niobium complexes have been calculated.On the basis of a detailed spectrophotometric study,the nature of the chromophoric reagent-surfactant interaction and the peculiar features of the sensitization by CPB are discussed.