A highly sensitive and selective first-derivative spectrophotometric method has been developed for the determination
of aluminum and iron in mixtures. The method is based on the formation of the binary complexes
of aluminum and iron with Alizarin yellow R (AYR) 5-[4-nitrophenylazo]salicylic acid at pH 2.0 with molar
absorptivity of 1.1⋅104 l⋅mol–1⋅cm–1. A zero-crossing technique is found suitable for the direct measurement of
the first derivative value at the specified wavelength, so aluminum and iron were thus determined in the
ranges 1.3–5.4 μg/ml and 1.1–8.3 μg/ml, respectively, in the presence of both components. The detection limits
were found to be 1.4 ng/ml for aluminum and 2.8 ng/ml for iron. The relative standard deviations were in
all cases less than 1.5%. The proposed method was successfully applied for the simultaneous determination of
aluminum and iron in certified reference aluminum samples