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已知锌(Ⅱ)离子在过量的SCN~-存在下可形成无色的[Zn(SCN)_4]~(2-)络阴离子。Kиш等利用[Zn(SCN)_4]~(2-)与孔雀石绿的离子缔合反应对锌进行萃取——光度法测定。由于反应在近中性的介质中进行,此时孔雀石绿基本上以绿色的单电荷阳离子MG~+形式存在。反应前后没有观察到水相发生颜色变化,显色反应仅发生在萃取后的有机相中,因而不能在水相中直接用光度法测定锌。但经实验发现,在有阿拉伯树胶、明胶或聚乙烯醇等保护胶体存在下的酸性溶液中,[Zn(SCN)_4]~(2-)与某些碱性三苯甲烷染
Zinc (II) ions are known to form colorless [Zn (SCN) 4] 2- (2) anions in the presence of excess SCN. Kiefer et al. Used zinc ion extraction-spectrophotometry with [Zn (SCN) 4] 2- (2-) and malachite green ion association reaction. Since the reaction is carried out in a nearly neutral medium, the malachite green is essentially present in the form of green single-charged cation MG ~ +. No color change was observed in the aqueous phase before and after the reaction, and the color reaction only occurred in the organic phase after the extraction. Therefore, it was impossible to measure the zinc directly in the aqueous phase by photometry. However, it has been found experimentally that the ratio of [Zn (SCN) 4] 2- and some basic triphenylmethane dyes in an acidic solution in the presence of a protective colloid such as gum arabic, gelatin or polyvinyl alcohol