الفهرس 
EXPERIMENTALOnly 14 pages are availabe for public view
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Abstract
In the present work, oxidized hematoxylin has been used for the spectophotometric dete1111ination of niobium(v) and tantalum(v). The inlluencc of some protective colloids and micellar systems of cationic, anionic and nonionic surfaetants, on the spectral characteristics has been investigated in order to select the optimum conditions for enhancing the ;1bsorbance of the corresponding complexes. Moreover, derivative spectrophotometric methods have been proposed for the individual and simultaneous detcnnination of niobium(v) and tantalum(v).
Simple and sensitive (zero-order) spectophotometrie methods have been developed for the detennination of niobium(v) in the absence and presence of a cationic surfactant. The absorbance of niobium(v)-oxidized hematoxylin complex increased about 3-folds in the presence of a micellar solution of cetyltrimethylammonium bromide (CTAB). The optimum pH ranges for the formation of binary and sensitized complexes are 7.4-7.8 and 8.0-8.4, respectively. The effect of reagent and surfactant concentrations, standing
time and foreign ions have been investigated .
The molar absorptivities ofniobium(v)-oxidized hematoxylin complexes, in the absence and presence of a micellar medium of CTAB, are3.00x I 04 and
9.02xl04 l.mo1•1 .cm•1 at 596 and 565 mn, respectively. The corresponding equations of the calibration graphs are A= 0.328 CNb + 0.0001 and A=
0.971 CNb + 0.002, respectively. The concentration of niobium(v) (CNb) is calculated in ppm units . The sensitivity index of the methods are 3.10 and 1.03 ng.cm-2, respectively . The molar ratio and continuous variation methods indicate a niobium(v): oxidized hematoxylin ratio of 1 :3 in the complex .