Preparation of soluble ternary heteroazo dye complexes for the spectrophotometric determination of trace uranium(VI)

The complexing ability of typical pyridylazo, quinolylazo and thiazolylazo dyes with uranium(VI) in aqueous ethanol media are investigated in the presence and absence of aromatic carboxylic acid. Uranium(VI) forms solubilized ternary complexes with PAN, PAR, TAM, 5-Br-PADAP, 3,5-diBr-PADAP and QADAP in 48% ethanol solution containing sufficient amounts of sulfosalicylic acid and triethanolamine buffer (pH 7.8). Aromatic carboxylic acids contribute to expel the coordinated water molecules from the uranium (VI) moiety and their chelating effects have been explained by ternary complex formation. An increase in molar absorptivity and no shift in the wavelength of maximum absorbance are observed for all uranium(VI) complexes investigated. The 11 stoichiometry of uranuim(VI) and heteroazo dye in the binary complex does not change through ternary complex formation. The molar absorptivity of the uranium(VI)-3,5-diBr-PADAP-sulfosalicylic acid ternary complex at 595 nm is 8.4×10⁴l mol^–1 cm^–1 and Beer's law is valid up to 2.5gmg ml^–1 of uranium(VI). The interferences due to coexisting metal ions can be effectively masked by addition of CyDTA or Ca-CyDTA.