Simultaneous determination of aluminum (III) and iron (III) by first-derivative spectrophotometry in alloys

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.