Study on discoloring spectrophotometry of cerium-dibromocarboxyarsenazo and its application

The discoloration reation of dibromocarboxyarsenazo oxidized strongly by trace Ce(Ⅳ)in H2SO4 medium occurs,and the fading rate is linear with the concentration of Ce(Ⅳ).In view of the above,a new discoloring spectrophotometry for the determination of trace Ce(Ⅳ)was developed.The results show that the maximum absorption wavelength and apparent molar absorptivity are 530 nm and 7.2 ×106 L·mol-1·cm-1,respectively.The linear range is 0.25 ～ 10 μg for Ce(Ⅳ)in 25 mL of solution,and the detection limit is 4.5 μg/L.The method has been directly applied to the determination of trace cerium in spheroidal graphite cast iron and alloys with RSD of 1.0%-3.6%,and the results are agreement with the certified values.