Spectrophotometric determination of barium in Si-Ba-Mg alloy with p-acetylchlorophosphonazo

The color reaction of barium with p-acetylchlorophosphonazo(CPApA) was studied.In 0.40 mol/L H3PO4 medium,p-acetylchlorophosphonazo reacts with barium(Ⅱ) to form a stable 2∶1 complex,whose maximum absorption wavelength is at 646 nm and apparent molar absorptivity is 1.35×105 L·mol-1·cm-1.Beer's law was obeyed in the range of 0-0.80 mg/L for barium.The barium content in Si-Ba-Mg alloy has been determined by this method,and the results are in good agreement with those provided by gravimetry.The relative standard deviation is less than 3% and the recoveries of samples are between 97.4% and 102.6%.