碘化物-亚甲基蓝-阿拉伯胶-聚乙烯醇体系分光光度法测定痕量铬(Ⅵ)

Spectrophotometric Determination of Trace Chromium(Ⅵ) Using the System of Iodide-Methylene Blue-gum Arabic-Polyvinyl Alcohol

在磷酸介质中,Cr（Ⅵ）氧化I-离子形成I3^-络阴离子,I3^-络阴离子进一步与亚甲基蓝形成离子缔合物,在阿拉伯胶-聚乙烯醇存在下,溶液清亮.以试剂空白参比,波峰λmax位于524 nm处,吸光度A与Cr（Ⅵ）的浓度成正比.表观摩尔吸收系数ε=7.41×104L·mol^-1·cm^-1,Cr（Ⅵ）含量为0～640μg·L^-1时服从比尔定律.方法用于环境水样中Cr（Ⅵ）检测,结果令人满意.

A highly sensitive spectrophotometric method has been developed for the determination of trace amounts of Chromium（ Ⅵ ） based on the oxidation of Ⅰ^- to Ⅰ3^- by Chromium（ Ⅵ ） and the further reaction of Ⅰ3^- with Methylene Blue to form the ion-association complex in dilute phosphoric acid solution. In the presence of gum Arabic and polyvinyl alcohol the solution was transparent. The Xmax of the absorption spectrum is at 524 nm against reagent blank. It was discovered that the absolute value of the Xmax is proportional to the Chromium（ Ⅵ ） concentration. The molar absorptivity iSE= 7.41 × 104 L · mol^-1 ·cm^-1 at 524 nm. Beer＇s law is obeyed in the range of 0～640 μg · L^-1. The method has been applied to the determination of Chromium（Ⅵ） in natural water, with satisfactory results.