耐尔蓝-钍钼杂多酸光度法测定钍

Spectrophotometric Determination of Thorium with Nile Blue and Molybdothorate Heteropoly Acid

本文研究超高灵敏光度法测定钍。在聚乙烯醇（PVA）存在下，耐尔蓝（NB）与钍钼杂多酸络阴离子形成离子缔合物。在1．2mol／L高氯酸介质中缔合物的最大吸收位于590nm，摩尔吸光系数ε值4．45×106L·mol－1·cm－1，钍量在0～28μg／L范围服从比耳定律；测定极限C（Th）3．4μg／L（n＝9）；对20μg／LTh分析9次的相对标准偏差1．5％；缔合物的摩尔组成Th：Mo：NB＝1：12：3。考察了50多种共存离子影响，允许100倍量Ce（Ⅲ）、50倍量U（Ⅵ）和等量Ti（Ⅳ）存在。本法用于地质样品中钍的测定，结果满意。

A sensitive spectrophotometric method for the determination of thorium is investigated. The ion-association complex is formed by the reaction of nile blue (NB) with heterdtoly molybdothoric acid in the presence of polyvinyl alcohol (PVA). The complex gives maximum absorbance at 590 nm in a solution containing 1. 2 mol/L perchloric acid. The apparent molar absorptivity of ion-association complex is 4. 45 ×106·mol-1·cm-1. Beer' s law is obeyed for 0～28 μg/L of thorium. The limit of detection is 3. 4 μg/L(n=9). A 0. 02 mg/L thorium sample is analysed nine tirnps and the relative standard deviation is 1. 5%. The molar composition of ion-association complex is found to be Th ： Mo: NB= 1: 12: 3. The influence of over 5o diverse ions was examined. There was no interference from 100-fold amount of Ce(Ⅲ), 50-fold amount of U(Ⅳ ) and 20-fold anlount of P(Ⅴ). The method has been applied to the determination of thorium in some geological samples. The results obtained agree well with recommended values and the recovery is also satisfactory.