碱性镀锌溶液中微量铅的测定

Datermination of Trace of Lead in Alkaline Zn Plating Bath

本文论述了碘化铅络阴离子与碱性有机染料结晶紫之间的缔合反应。在某些特殊型表面活性剂,如阿拉伯树胶、聚乙烯醇或其混合溶液的存在下,离子缔合物溶于水,并伴有极灵敏的颜色变化。最大吸收峰位于530μm,表观摩尔吸光系数高达1.34×10~5。铅在0～12微克/25毫升范围内遵守比耳定律。适宜的酸度范围为pH1.5～2.0。大多数金属离子不干扰测定,铁离子必须用抗坏血酸还原成低价。Cu^(2+),Hg^(2+),Ag^+,Bi^(3+),Sn^(2+),Sb^(3+)等金属离子能用抗坏血酸-硫脲和磷酸-磷酸氢二钠溶液掩蔽,但Cd^(2+)与C10_4^-强烈干扰测定,所以必须注意。该法已用于直接测定碱性镀锌溶液中的微量铅,并获得了满意的结果。

The association of lead iodide complex anion and crystal violet (a basic organic dye) is studied. In the presence of some special surfactants such as Arabic gum, polyvinyl alcohol or their mixture, the associated ion is soluble in water, accompanied with very sensitive color change. Its absorption peak lies in 530μm and apparent molar absorption coeffi- cient is up to 1.3×10~5. Lead will obey Beer's Law in the range of 0-12 μg/25 mL. The preferable pH is 1.5-2.0. Most of the metal ions have no interference on the determin- ation. Ferric ion must be reduced to its lower valence with ascorbic acid and the other metal ions such as Cu^(2+), Hg^(2+), Ag^+, Bi^(3+), Sn^(2+) and Sb^(3+) can be masked by ascorbic acid-thiourea and phosphoric acid-sodium dihydrogen phosphate. However, Cd^(2+) and ClO_4^- have serious effects on the determination so that care must be taken when they exist. This method has been used in the determination of micro lead in zinc plating bath, and proved to be satisfact- ory.