On the suitability of Portable X-Ray Fluorescence Analyzers for rapid screening of toxic

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Abstract
X-Ray Fluorescence spectrometry (XRF) has been routinely used for alloy testing, determination of Pb in paint, and determination of Cd in plastic. However, its use to screen for toxic elements in food and medicinal products has been surprisingly limited to date. While XRF is less sensitive than atomic spectrometry methods such as ICP-AES and ICP-MS, it offers a number of significant advantages including minimal sample preparation, rapid analysis times, multi-element detection, and true field use using hand-held analyzers. The goal of this study was to evaluate the capabilities and limitations of two different portable XRF analyzers from Niton and Innov-X. The samples chosen for this study included liquid, semi-solid, and solid substances (cranberry juice, yogurt, and chocolate). Samples were fortified with up to four different toxic elements (arsenic, lead, mercury, and/or selenium) to give known concentrations on a weight-weight basis. Samples were analyzed via XRF and the resulting data were evaluated to ascertain figures of merit including selectivity, limits of detection (LODs), linear dynamic range, accuracy, precision, and speed. Selectivity was generally good and positive detection can be confirmed through the observation of multiple emission lines for an element. Although accurate quantitation of multiple elements may be compromised by overlap of emission lines, one would generally not expect to see the presence of several toxic elements in a given product. The sensitivity of the Innov-X analyzer was nearly an order of magnitude better than the Niton, with LODs in the 5-10 ppm range for all four target elements. Calibration curves were linear across more than three orders of magnitude spanning concentrations from the LOD out to percent levels. The accuracy of the Innov-X analyzer was slightly better than the Niton, with relative errors typically less than 20%, which is particularly remarkable considering that no external calibration procedures were employed and these results were obtained using the manufacturer’s standard quantitation algorithms. Precisions were quite good as well, with percent relative standard deviations (%RSDs) of 5% or less. The most attractive features of XRF are its speed and simplicity, with minimal sample preparation required, analysis times as short as a minute or less, and estimated throughputs of approximately 60 samples per hour using a device that is hand-held and can be operated by a non-expert. Collectively, these capabilities make XRF a powerful tool for screening of toxic elements and rapidly responding to emergency situations that require identification and quantitation of toxic elements.

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