Study on the Dual-Wauelengih Spectrophotometry of Al-EBT-OP Complex and Its Application

Against a reagent blank, the purple Al-EBT-OP complex at pH 6 exhibits maximal positive and negative absorption peaks at 625 nm and 688 nm respectively. The absorbance difference ΔA is proportional to Al concentration in the range 5-80μg/100ml, with an apparent molar absorptivity of 5.3×104. The molar ratio of Al to EBT is 1:3, and the complex is stable for at least a week. The aluminum signal is measured at 628 nm and 688 nm, to take advantage of the isoabsorptive behavior of Fe(III) complex at both wavelengths. This method has been applied to the determination of major aluminum in silicate rocks and minerals with satisfactory results. The standard deviation and relative stadard deviation for a sample containing 16. 44%Al2O3 are 0.149% and 0.91% respectively (n=18).