Abstract This article analyzes the various components of uncertainty in the determination of cadmium content in rice using energy dispersive X-ray fluorescence spectrometry, and analyzes the sources of measurement uncertainty. Measurement uncertainty mainly comes from standard materials and working curve fitting. The uncertainty components are evaluated, and the combined standard uncertainty and expanded uncertainty are calculated. When the cadmium content in rice is 0.268 mg/kg, the expanded uncertainty is 0.029 mg/kg (k=2)

In the realm of environmental science and food safety, accurate measurement of toxic metal content in foodstuffs is paramount. Among these, the determination of cadmium (Cd) in rice is critical due to its potential health impacts. This paper delves into the evaluation of uncertainty components in measuring cadmium content in rice utilizing Energy Dispersive X-Ray Fluorescence Spectrometry (EDXRF). Understanding and quantifying the sources of measurement uncertainty is vital for ensuring the reliability and comparability of analytical results.

Background

Cadmium is a toxic heavy metal that can accumulate in rice, one of the staple foods worldwide, posing a significant risk to human health. Accurate determination of cadmium content is essential for food safety assessments and regulatory compliance. EDXRF offers a non-destructive, rapid, and relatively simple method for this purpose. However, like any analytical technique, it is subject to measurement uncertainty, which must be meticulously evaluated and minimized.

Sources of Measurement Uncertainty

The primary sources of measurement uncertainty in the determination of cadmium content in rice using EDXRF have been identified as standard materials and working curve fitting. Standard materials, used to calibrate the EDXRF instrument, can introduce uncertainty due to their own compositional inhomogeneity and the accuracy of their certified values. Working curve fitting, essential for translating the X-ray fluorescence intensities into concentration values, introduces uncertainty through the mathematical model used, the selection of calibration points, and the inherent variability in the response of the EDXRF instrument.

Evaluation of Uncertainty Components

To rigorously evaluate the uncertainty components, this study employed the Guide to the Expression of Uncertainty in Measurement (GUM) methodology. This approach involves the identification and quantification of each source of uncertainty, followed by the calculation of the combined standard uncertainty. The combined standard uncertainty is a quantitative expression of the overall uncertainty associated with the measurement result, taking into account the various identified sources.

Results

When applied to the determination of cadmium content in rice, with a measured value of 0.268 mg/kg, the expanded uncertainty was calculated to be 0.029 mg/kg (with a coverage factor, k=2), which corresponds to a 10.8% relative uncertainty. This value provides an indication of the reliability of the measurement, encompassing the major identified sources of uncertainty.

Conclusion

The evaluation of measurement uncertainty is a fundamental aspect of ensuring the quality and reliability of analytical results. By identifying and quantifying the sources of uncertainty in the determination of cadmium content in rice using EDXRF, this study contributes to the ongoing efforts to improve food safety. The findings underscore the importance of considering both standard materials and working curve fitting as significant contributors to measurement uncertainty. Future work should focus on refining the methods for evaluating these sources of uncertainty and exploring strategies to minimize their impact, thereby enhancing the accuracy and reliability of cadmium content determination in rice and other foodstuffs.

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Original research was done by 10.3969/j.issn.1006-8082.2018.02.015

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