在pH 3.6 NaAc-HAc缓冲溶液中,Cd~(2+)与过量的KI和吖啶橙(AO)反应生成稳定的离子缔合物[AO]_2[CdI_4],体系吸光度明显增强,建立了分光光度法测定痕量镉的新方法.试验了酸度、试剂用量、表面活性剂、温度和时间的影响,确定了最佳测定条件.最大吸收峰位于484 nm,线性范围为0～0.4μg/mL,表观摩尔吸光系数为1.66×10~5L·mol~(-1)·cm~(-1),检出限为6.82μg/L.大量的常见离子不干扰测定,MnO_4~-、Pb~(2+)、Fe~(3+)和Hg~(2+)的干扰可采用抗坏血酸-巯基棉分离去除.方法用于测定河水中镉,结果与原子吸收光谱法一致.相对标准偏差为1.7%～2.0%(n=5),回收率为98%～100%.
A new spectrophotometric method was developed for the determination of trace cadmium . The method was based on the reaction of Cd~(2+) with excess KI and acridine orange (AO), which forms a stable ion-association complex [AO]_2[CdI_4] in NaAc-Hac buffer solution at pH 3. 6, resulting in a great enhancement of absorbance in the maximum absorption peak at 484 nm. The optimal conditions including acidity, reagents dosage, surfactant, temperature and time were studied. The linear range was 0-0.4 μg/mL. The apparent molar absorptivity was 1.66 × 10~5L·mol~(-1)·cm~(-1) and the detection limit was 6.82μg/L. A great deal of coexistent ions didn't interfere with the determination. The interferences of MnO_4~- , Pb~(2+) , Fe~(3+) and Hg~(2+) could be separated by ascorbic acid-thiohydroxy cotton fiber. The method was applied to the determination of cadmium in river water samples. The results well agreed with those obtained using atomic absorption spectrometry (AAS). The relative standard deviations of 5 determinations were 1.7%-2.0% and recoveries were 98%-100%.
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