Determination of cadmium concentrations in agricultural products by high-sensitivity energy-dispersive X-ray fluorescence spectrometry and use of the method for screening rice grains

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  • 高感度エネルギー分散型蛍光X線分析装置による農産物中カドミウム濃度の測定とスクリーニング分析への適用
  • コウカンド エネルギー ブンサンガタ ケイコウ Xセン ブンセキ ソウチ ニ ヨル ノウサンブツ チュウ カドミウム ノウド ノ ソクテイ ト スクリーニング ブンセキ エ ノ テキヨウ

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We report a method for rapid, efficient determination of sub-parts-per-million concentrations of Cd in rice flour by means of high-sensitivity, energy-dispersive X-ray fluorescence (EDXRF) spectrometry. The detection limit for Cd in rice flour was 0.07 mg kg^<-1> at a measurement time of 1200 s. The calibration curve for Cd in rice flour showed good linearity (R^2=0.9997), and the results obtained by analysis of reference materials by the EDXRF method agreed with certified values. Furthermore, precision and accuracy were within acceptable ranges: Horowitz ratios were <2, and the expanded uncertainty (95% confidence interval) values were within the absolute value of the difference between the measured and certified values. The Cd concentrations determined by EDXRF for ten samples of rice containing Cd at concentrations ranging from 0.05 to 2.42 mg kg^<-1> agreed with the values determined by atomic absorption spectrometry. These results indicate that the EDXRF method has sufficient accuracy for the analysis of Cd at sub-parts-per-million concentrations. Additionally, the rice calibration curve could be effectively used to determine Cd concentrations in other crops, such as soybeans, wheat, okra, garland chrysanthemum, cabbage, and Japanese taro. With this method, the time required to determine whether the Cd concentration in rice grains exceeded the maximum level (0.4 mg kg^<-1>) was drastically shorter than the time required for previous reported methods. For instance, analysis of rice containing 0.1 mg kg^<-1> Cd required only 71 s, and 158 and 619 s were required for rice containing 0.2 and 0.3 mg kg^<-1> Cd, respectively. Moreover, no differences in Cd concentration were observed between unmilled rice and rice flour. These results suggest that the rapid screening of rice by means of EDXRF is a practical method for preventing rice containing high levels of Cd from making it to the market.

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