痕量碘离子的铬(Ⅵ)-碱性呫吨染料体系分光光度法测定

Spectrophotometric Determination of Trace Amount of Iodidewith Chromium(Ⅵ)-Bromide-Basic Xanthene Dye System

在过量溴化物存在下的稀磷酸介质中 ,I-被Cr(Ⅵ )氧化成I2 后与Br-结合形成[I2Br] -配阴离子 ,该配阴离子能进一步与罗丹明6G、罗丹明B、吖啶红等碱性吨染料阳离子形成离子缔合配合物。在聚乙烯醇存在下 ,缔合物体系稳定且溶液颜色有明显的变化 ,可用于I-离子的光度测定。方法具有高灵敏度 ,不同体系的摩尔吸光系数在4 .96×104 ～1 .1×105 L·mol-1·cm-1 之间 ,以罗丹明6G和罗丹明B体系灵敏度较高。碘离子质量浓度分别在0～0.8mg/L(罗丹明B和罗丹明6G体系)、0～1.0mg/L(吖啶红体系 )之间遵守比尔定律。方法具有良好的选择性 ,用于海带。

In dilute phosphoric acid medium, chromium(Ⅵ) oxidizes I- to I2, which then binds Br- to form - anion in the presence of excess bromide, and - anion further reacts with basic xanthene dyes such as rhodamine 6G, rhodamine B and acridine red to form ion _ association complexes. In the presence of polyvinyl alcohol(PVA) the solution is stable and a distinct color change occurred. The method can be applied to the spectrophotometric determination of iodide. The method have a high sensitivity and selectivity. Its molar absorptivity is 1.1×105 L·mol-1·cm-1 for rhodamine 6G and rhodamine B systems, and 4.96×104 L·mol-1·cm-1 for acridine red system. The Beer’s law is obeyed in the range over 0～0.8 mg/L and 0～1.0 mg/L of I- for rhodamine 6G, B systems, and acridine red system, respectively. It was used to determine I- in kelp, soybean and cydiodine tablets with satisfactory results.