Analytical application of the complexation of Nb(V) with Bromopyrogallol Red in micellar media

A spectrophotometric method for the determination of trace amounts of Nb(V) based on the formation of a ternary complex with Bromopyrogallol Red (L) and cetylpyridinium bromide (CPB) in 1M hydrochloric acid/15% dimethylformamide medium has been developed. The ternary 1:2:2 Nb-L-CPB complex is formed. The absorbance maximum is at 645 nm, the molar absorptivity being (4.00 +- 0.04) x 104 l.mole-1.cm-1. The relative standard deviation is 1.9% and Beer's law is obeyed up to 1.4 μg of Nb(V) per ml. The application of the method to the determination of Nb in pyrochlore-bearing rocks is described. A possible mechanism of interaction of the surfactant with the Nb-L complex is discussed. (author)