Determination of Cadmium in Shrimp and Shell Fish Samples by Coprecipitation Enrichment with Mn(Ⅱ)-5-Br-PADAP Flame Atomic Absorption Spectrometry.

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.