Use of Field-Portable XRF Analyzers for Rapid Screening of Toxic Elements in FDA-Regulated Products

Analytical instrumentation continues its amazing evolution, especially in regard to generating ever more sensitive, faster, and reliable measurements. Perhaps the most difficult challenges are making these instruments small enough to use in the field, equipping them with well-designed software that facilitates and simplifies their use by nonexperts while preserving enough of their analytical capabilities to render them useful for a wide variety of applications. Perhaps the most impressive and underappreciated example of instruments that meet these criteria are field-portable X-ray fluorescence (XRF) analyzers. In the past, these analyzers have been routinely used for environmental applications (lead in paint and soil, metal particulates in air samples collected onto filters), geology studies (ore and soil analysis, precious metal identification), and recycling industries (alloy identification). However, their use in the analysis of toxic elements in food, food ingredients, dietary supplements, and medicinal and herbal products, especially within the FDA and regulatory environments, has been surprisingly limited to date. Although XRF will not replace atomic spectrometry techniques such as ICP-MS for sub-parts per million level analyses, it offers a number of significant advantages including minimal sample preparation, high sample throughputs, rapid and definitive identification of many toxic elements, and accurate quantitative results. As should be obvious from many recent news reports on elevated levels of toxic elements in children's lunchboxes, toys, and supplements, field-portable XRF analyzers can fill a very important niche and are becoming increasingly popular for a wide variety of elemental analysis applications. This perspective begins with a brief review of the theory of XRF to highlight the underlying principle, instrumentation, and spectra. It includes a discussion of various analytical figures of merit of XRF to illustrate its strengths and limitations compared to existing methods such as ICP-MS. It concludes with a discussion of a number of different FDA applications and case studies in which XRF has been used to screen, identify, and in some cases quantify toxic elements in various products. This work clearly demonstrates that XRF analyzers are an exceedingly valuable tool for routine and nonroutine elemental analysis investigations, both in the laboratory and in the field. In the future, it is hoped that both field-portable and laboratory-grade XRF analyzers will see more widespread use for investigational and forensic-type applications of food and other regulated consumer products.