Discoloring spectrophotometric determination of magnesium in aluminium alloys with chlorophosphonazo III

Based on the discoloring reaction between magnesium and chlorophosphonazo Ⅲ(CPA-Ⅲ) in pH 10.0 NH3·H2O-NH4Cl medium,a discoloring spectrophotometry for the determination of magnesium in aluminium alloy is established.The effects of the factors such as absorption spectra,acidity,concentrations of reagent,influence of coexisting ions on the reaction are discussed,and the reaction conditions are optimized.The calibration curve is linear in the range of 0-16 μg/25 ml for magnesium.Large amounts of aluminium,iron and certain amounts of manganese,copper can be tolerated in the presence of the masking reagent,like triethanolamine,phenanthroline and EGTA-pb salt.Other coexistent elements in aluminium alloy do not interfere in the determination.The proposed method can be applied to the determination of magnesium in aluminium alloys,with the RSD(n=5) between 1.4% and 2.1%.