Highly sensitive spectrophotometric determination of trace amounts of aluminium with chromazol KS and cetylpyridinium bromide

Abstract

A highly sensitive spectrophotometric method has been developed for the determination of aluminium, based on the formation of a ternary complex with chromazol KS (CALKS) and cetylpyridinium (CP) bromide in aqueous solution in the presence of 25–40% of ethanol. The pH range for the formation of the ternary complex is 5.8–6.7, and the wavelength of maximum absorbance is 625 nm. The ternary system obeys Beer's law for between 0.02 and 0.32 µg ml^–1 of aluminium. A high molar absorptivity of ε= 1.02 × 10⁵ l mol^–1 cm^–1 and a Sandell's sensitivity of 0.00026 µg cm^–2 have been obtained. The complex has the composition Al(OH)(CALKS)₂(CP)₆, as established by Job's method of continuous variation and the equilibration shift method. The method has good selectivity and so can be applied to the direct spectrophotometric determination of trace amounts of acid-soluble aluminium in steel.