Simultaneous determination of aluminium and iron in glasses, phosphate rocks and cement using first and second derivative spectrophotometry

First- and second-derivative spectrophotometric methods for the simultaneous determination of aluminium and iron in their mixtures are described. The methods are based on the colored complexes formed by aluminium and iron with hematoxylin in the presence of cetyltrimethylammonium bromide as a surfactant. The zero-crossing method has been utilized to measure the first- and second-derivative value of the derivative spectrum. Aluminium (0.05-1 mu g ml(-1)) could be determined in the presence of iron (0.09-1.6 mu g ml(-1)) and vice versa. The detection limits of aluminium and iron are 0.01 and 0.09 mu g ml(-1), respectively in the first-derivative mode and 0.014 and 0.1 mu g ml(-1) in the second-derivative mode. The proposed method has been applied to the simultaneous determination of aluminium and iron in glasses, phosphate rocks, cement and magnesite alloy.