镉的高灵敏显色体系研究及表面活性剂作用机理

本文以2-氯-4-硝基苯重氮氨基偶氮苯(CNDAA)为显色剂, 研究了镉的高灵敏显色体系及表面活性剂的作用机理。研究结果表明: 对于Cd(II)-CNDAA配合物, 非离子型、阴离子型及阴-非混合型表面活性剂对此有显著的增溶增敏作用, 并以Cd(II)-CNDAA-SF显色体系建立了光度法测定微量镉的高灵敏新方法, 并对几种测定方法进行了比较, 筛选出显色条件宽容、选择性好的体系。该体系用于铝合金样品中镉的测定, 结果满意。另外, 还提出了Cd(II)-CNDAA配合物的结构, 对表面活生剂对体系的作用作了描述, 并阐明了试剂的酸性离解常数(pK~a)与显色酸度以及方法的选择性三者之间的关系。

Study on a highly sensitive color reaction of cadmium and the action mechanism of surfactants

A highly sensitive color reaction of cadmium and the action mechanism of surfactants were studied by using 2-chloro-4-nitrobenzenediazoaminoazobenzene (CNDAA) as chromogenic reagent. It was shown that Cd(II)-CNDAA complex could be solubilized and sensitized by nonionic surfactants, anionic surfactants and nonionic-anionic mixed surfactants. Four new methods for spectrophotometric determination of trace cadmium were built based on the system of Cd(II)-CNDAA-SF. The proposed method has a high sensitivity, good selectivity and a wide acidity range of color reaction and were used for determination of trace cadmium in aluminum alloy with satisfactory results. Moreover, the structure of Cd(II)-CNDAA complex was investigated. The relationship between the dissociation constant of reagent (pKa), acidity of color reaction, and the selectivity of method were also described.