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用5-Br-PADAP(简称Br-PADAP)分光光度法测定铀已有不少研究,大部分选择在乙醇或丙酮介质中显色;也有用非离子表面活性剂增溶后在水相中显色,但选择性并无多大改进。我们研究了阳离子表面活性剂之一:溴化十六烷基吡啶(简称CPB)增溶的Br-PADAP分光光度法测定铀的条件。在含有CPB的微碱性介质中,U(Ⅵ)与Br-PADAP迅速显色,络合物组成约为U:Br-PADAP:CPB=1:1:13;在590nm处呈最大吸收;摩尔吸光系数可达8.5×10~4(在Unicam SP800自动记录光度计),为原法的1.2倍,在721型光度计上ε为7.2×10~4。桑德尔灵敏度为0.0028μgU·cm~(-2),铀浓度为0～2.4μg·ml~(-1)时符合比尔定律。方法除可允许存在较大量的钍、希土等离子外,还可允许较多的磷酸根、铬(Ⅵ)和钒(Ⅴ),从而可直接测定包括一定含磷量的多种矿样中的铀。经适当分离手段,方法可测低至ppm级的铀。
Many studies have been conducted on the determination of uranium by 5-Br-PADAP (Br-PADAP) spectrophotometry, most of which have been developed for color development in ethanol or acetone media. Also useful are nonionic surfactants that solubilize in the aqueous phase Color, but selectivity has not improved much. We studied the determination of uranium by Br-PADAP spectrophotometry, one of the cationic surfactants, solubilized with cetylpyridinium bromide (CPB). In the slightly alkaline medium containing CPB, U (Ⅵ) and Br-PADAP rapidly developed color, the complex composition was about U: Br-PADAP: CPB = 1: 1: 13; Absorbance coefficient of up to 8.5 × 10 ~ 4 (Unicam SP800 automatic recording photometer), 1.2 times the original method, in the 721 photometer ε is 7.2 × 10 ~ 4. Beer’s law is obeyed when the sensitivity of Sander is 0.0028μgU · cm -2 and the concentration of uranium is 0 ~ 2.4μg · ml -1. The method allows more phosphate, chromium (Ⅵ) and vanadium (Ⅴ) to be allowed in addition to larger amounts of thorium and rare earth ions and thus allows direct determination of uranium. By appropriate means of separation, the method can be measured down to ppm uranium.