Palmer Peter T, Jacobs Richard, Baker Peter E, Ferguson Kelly, Webber Siri
Department of Chemistry and Biochemistry, San Francisco State University, San Francisco, California 94132, USA.
J Agric Food Chem. 2009 Apr 8;57(7):2605-13. doi: 10.1021/jf803285h.
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.
分析仪器继续着其惊人的发展，尤其是在实现更灵敏、更快速且更可靠的测量方面。或许最具挑战性的难题在于，要将这些仪器做得足够小巧以便能在现场使用，为其配备精心设计的软件，既能方便非专业人员使用并简化操作，又能保留足够的分析能力以适用于各种应用。符合这些标准的仪器中，最令人印象深刻且未得到充分重视的例子或许当属现场便携式X射线荧光（XRF）分析仪。过去，这些分析仪常规用于环境应用（油漆和土壤中的铅、收集在滤纸上的空气样本中的金属微粒）、地质研究（矿石和土壤分析、贵金属鉴定）以及回收行业（合金鉴定）。然而，迄今为止，它们在食品、食品成分、膳食补充剂以及药用和草药产品中有毒元素分析方面的应用，尤其是在FDA及监管环境下，出人意料地有限。尽管对于百万分之一以下水平的分析，XRF无法取代诸如电感耦合等离子体质谱（ICP-MS）等原子光谱技术，但它具有诸多显著优势，包括样品制备极少、样品通量高、能快速明确鉴定多种有毒元素以及获得准确的定量结果。从近期许多关于儿童午餐盒、玩具及补充剂中有毒元素含量升高的新闻报道中可以明显看出，现场便携式XRF分析仪能填补一个非常重要的空白，并且在各种元素分析应用中越来越受欢迎。本视角首先简要回顾XRF理论，以突出其基本原理、仪器设备及光谱。它包括对XRF各种分析性能指标的讨论，以说明与诸如ICP-MS等现有方法相比其优势和局限性。最后讨论了一些不同的FDA应用及案例研究，其中XRF已被用于筛查、鉴定，在某些情况下还用于量化各种产品中的有毒元素。这项工作清楚地表明，XRF分析仪对于实验室和现场的常规及非常规元素分析研究而言，都是极为有价值的工具。未来，希望现场便携式和实验室级XRF分析仪在食品及其他受监管消费品的调查和法医类应用中能得到更广泛的使用。
