在硝酸介质中,铬(Ⅵ)与二溴对甲基偶氮磺生成1∶3物质的量比的稳定络合物,导致显色剂二溴对甲基偶氮磺吸光度降低,据此建立了褪色光度法测定铝合金中铬(Ⅵ)含量.对反应介质的种类和酸度、显色剂的用量、反应时间、共存离子的干扰等影响因素进行了试验并予以优化.在530 nm波长测定时,铬(Ⅵ)的质量浓度在0.032~0.48 mg·L-1范围内,反应体系吸光度的降低值ΔA与铬(Ⅵ)浓度呈线性关系,表观摩尔吸光率为4.34×104L·mol-1·cm-1.用于直接测定铝合金中微量铬的含量,测定值与标准值相符.相对标准偏差(n=8)小于2%.

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%.