提出了一种测量痕量重金属镉的新方法。 该方法创新性地以Mn(Ⅱ)作为载体离子, 以2-(5-溴-2-吡啶偶氮)-5-二乙氨基苯酚(5-Br-PADAP)作为共沉淀剂, 共沉淀分离富集虾、 贝样品中的镉, 同时采用火焰原子吸收法进行测定。 重点探讨了共沉淀剂加入量、 载体离子加入量、 pH值、 共沉淀时间、 共存离子的干扰等因素对共沉淀分离富集效果的影响, 从而确定了Mn(Ⅱ)-5-Br-PADAP共沉淀分离富集测定镉的最佳共沉淀条件。 实验结果表明, 当pH 7且大量干扰离子存在的条件下, Mn(Ⅱ)-5-Br-PADAP体系对镉有良好的共沉淀分离富集效果, 很好地克服了基体干扰。 共沉淀体系中镉含量在0.1～1.0 mg·L-1范围内时镉含量与吸光度呈线性关系。 该方法的灵敏度为0.147(mg·L-1)-1, 精密度为0.73%, 对镉的检出限(3σ)为4.27 μg ·L-1。 食品样品比较复杂, 对其中痕量重金属含量的测定必须经过消化、 分离富集等一系列预处理过程才能得到最准确地答案。 所以通过对比直接用火焰原子吸收法与应用本方法测定样品中镉含量的区别, 进一步说明了Mn(Ⅱ)-5-Br-PADAP体系对样品中重金属镉有很好的分离富集效果。 根据该方法, 采用标准加入法测得干贝样品中镉的含量为1.85 mg·kg-1, 干虾样品中镉的含量为1.74 mg·kg-1, 基本符合国际食品法典委员会的标准。 为了证明该方法的可靠性与真实性, 做了加标回收实验, 结果显示干虾干贝样品中镉的加标回收率范围为99.9%～100.3%, 相对标准偏差为0.15%～0.83%。 用Mn(Ⅱ)-5-Br-PADAP共沉淀分离富集样品中的痕量镉具有重现性好、 准确度高、 简单快速等的优点, 分析结果令人满意。

A separation/preconcentration procedure with coprecipitation has been proposed for the flame atomic absorption spectrometric (FAAS) determination of cadmium at trace level in food and environmental samples. Manganese(Ⅱ) was used as a carrier which chelated with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol to detect the content of trace cadmium in shrimp and shell fish samples with flame atomic absorption spectrometry for the first time. The precipitate could be easily dissolved with concentrated nitric acid. The optimum coprecipitation of this new method including the amount of reagent, amount of manganese(Ⅱ), the pH, and the standing time of the precipitate had been confirmed for the quantitative recoveries of the analytes. The effect of matrix ions and the interference of co-existing ions were also evaluated. Under the experimental conditions established by the optimization step, the system of Mn(Ⅱ)-5-Br-PADAP was able to overcome the matrix interference which showed the effect of separation and enrichment well. The linear range of cadmium content was determined to be 0.1～1.0 mg·L-1. The sensitivity and the relative standard deviation(RSD) were found 0.147(mg·L-1)-1, 0.73%, respectively. The optimum procedure allows the determination of cadmium with limit of detection of 4.27 μg·L-1. The complexity of preprocessing was determined by the complexity of food samples. So the differences of cadmium content in the samples between the direct determination with atomic absorption spectrometry and the measurement after coprecipitation were examined, which providedevidences for the superiority of the system again. Cadmium in shell fish and shrimp samples were 1.85 mg·kg-1 and 1.74 mg·kg-1, which in line with international standards of the Codex Alimentarius Commission(CAC). The credibility of the method was evaluated by standard additional method and recovery experiments. The standard addition recoveries of sample and RSDs of the method were in the range of 99.9%～100.3% and 0.15%～0.83%. The results of recovery experiment showed that the presented coprecipitation procedure had good repetition, high accuracy. In addition, with the method, we could draw conclusions that the experiments were simple and rapid. The developed method described in the literature was successfully applied for the determination of trace cadmium in shrimp and shell fish samples with satisfactory results.