Supercritical Fluid Extraction: A Non-Destructive Pre-Treatment Method for Plasma Oxidation & AMS Radiocarbn Dating

在国家科学基金会的支持下，阿肯色州中部大学的凯伦·斯蒂尔曼博士和凯尔·费林博士以及费耶特维尔阿肯色州大学的杰里·金博士将研究使用超临界流体去除考古文物中的有机污染物。这将进一步发展非破坏性放射性碳测年方法。这项研究将汇集来自化学和化学工程不同领域的教师和本科生，并加强与地球仪考古学家的合作。当考古文物进行放射性碳年代测定时，通常要经历三个独立的步骤：（1）化学预处理，以去除污染或分离样品特定的化学化合物;（2）将碳转化为可测量的形式;和（3）测量14 C以确定年龄。步骤1和2最广泛使用的方法是酸-碱-酸处理（阿坝），然后燃烧样品，这两种方法都是破坏性的。等离子体氧化提供了非破坏性地从人工制品表面收集微量碳的能力。超临界流体萃取，特别是使用二氧化碳（scCO 2）的超临界流体萃取，与传统的溶剂萃取相比具有以下优点：清洁，没有表面张力效应，最大限度地减少了处理样品的变形，并迅速扩散通过材料。通过控制压力和温度，可以调节流体的溶剂化强度，以优先溶解工件表面上的不同污染物和被整个材料吸收的污染物。scCO 2提取和等离子体氧化的结合使用有可能解决考古学家在处理稀有、独特或神圣物品时面临的主要问题之一--将文物放置在安全的年代背景下的需要往往被不愿意破坏甚至是必须使用当前测年方法进行燃烧的小部分所抵消。此外，通过探索放射性碳测年的非传统化学预处理，将实现对有机物质从各种基质中分离的更深入理解。本提案中概述的初始项目将提供一个知识基础，以应用于未来的研究，例如文物的保护或清洁以及从美国原住民物品中去除杀虫剂以供遣返。研究人员实验室的本科生将受益于这些先进的技术和研究。促进科学和考古学在阿肯色州的状态是至关重要的培养训练有素的专业人员在这些领域，特别是在一所大学，约18%的学生来自县在最低的四分之一的人均收入和从历史上萧条的密西西比三角洲地区的状态。需要更多的科学家将化学知识应用于考古和文化应用。

With National Science Foundation support, Drs. Karen Steelman and Kyle Felling of the University of Central Arkansas and Dr. Jerry King of the University of Arkansas at Fayetteville will investigate the use of supercritical fluids to remove organic contamination from archaeological artifacts. This will further develop non-destructive radiocarbon dating methods. The research conducted will bring together faculty and undergraduate students from diverse areas of chemistry and chemical engineering, as well as strengthening collaboration with archaeologists across the globe.When an archaeological artifact is radiocarbon dated, it typically undergoes three separate steps: (1) chemical pre-treatment to remove contamination or isolation of sample-specific chemical compounds; (2) conversion of the carbon to a measurable form; and (3) measurement of 14C to determine age. The most widely used methods for steps 1 and 2 are acid-base-acid treatments (ABA) followed by combustion of the sample, both of which are destructive. Plasma oxidation provides the ability to collect microscopic amounts of carbon from an artifact surface non-destructively. A need for an equally non-intrusive pre-treatment method to remove organic contamination is also essential.Supercritical fluid extraction, specifically with the use of carbon dioxide (scCO2), has advantages over a traditional solvent extraction in that it is clean, has a lack of surface tension effects which minimizes distortion of treated samples, and diffuses rapidly through materials. Through manipulation of pressure and temperature, the solvating strength of the fluid can be adjusted to preferentially dissolve different contaminants both on the artifact surface and those that are absorbed throughout the material. The combined use of scCO2 extraction and plasma oxidation has the potential to resolve one of the major problems facing archaeologists working with rare, unique, or sacred objects - the need to place artifacts in a secure chronological context is often offset by a reluctance to destroy even the small part that must be removed for combustion using current dating methods. Furthermore, by exploring non-traditional chemical pre-treatments for radiocarbon dating, a deeper understanding of separations of organic matter from a variety of matrices will be achieved. The initial project outlined in this proposal will give a knowledge base upon which to apply to future studies, such as the conservation or cleaning of artifacts and removal of pesticides from Native American items for repatriation.Undergraduate students in the researchers' laboratories will benefit from exposure to these advanced technologies and research. Promoting science and archaeology within the state of Arkansas is crucial to developing trained professionals in these fields, especially at a university where ~18% of students come from counties in the lowest quartile of per capita income and from the historically depressed Mississippi Delta region of the state. More scientists with interests in applying chemical knowledge to archaeological and cultural applications are needed.