Micro-determination of uranium(VI) based on the formation of a ternary complex with pyrogallol red and cetylpyridinium chloride

A sensitive spectrophotometric method has been developed for the microdetermination of uranium(VI) based on the formation of a blue ternary complex with pyrogallol red and cetylpyridinium chloride. The ternary complex is stable over the pH range 5.2–6.4, and the wavelength of maximum absorption is at 580 nm. The ternary system obeys Beer's law between 0.23 and 9.52 p.p.m. of uranium. A high molar absorptivity (ε= 36 500 l mol–1 cm–1) and Sandell's sensitivity (0.001 µg cm–2) have been obtained. The complex has the composition UO22+(PGR)2(CP)4, as established by Job's method of continuous variation and the molar ratio method. The method has been tested in the presence of several other cations and anions. The structure of the ternary complex is discussed.