Photometric Determination Chromium in Aluminium Alloy by Color-fading Reaction of Dibromo-p-methylsulfonazo

A stable complex was formed by the reaction of Cr(Ⅵ) with dibromo-p-methylsulfonazo in the mole ratio of 1 to 3 in dil.HNO3 solution,leading to decrease of absorbance of dibromo-p-methylsulfonazo as color reagent.Influtential factors,including the kinds and concentration of acid in the reaction medium,amount of color reagent,time of reaction,and interference of co-existing ions,were studied and optimized.Linear relationship between the magnitude of decrease in absorbance at 530 nm and the mass concentration of Cr(Ⅵ) was obtained in the range of 0.032-0.48 mg·L-1,and value of apparent molar absorptivity found was 4.34×104L·mol-1·cm-1.The proposed method was used in the determination of Cr(Ⅵ) in aluminium alloy,the results obtained was checked quite well with the standard values,and values of RSD′s (n=8) were less than 2.0%.