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

在美国国家科学基金会的支持下，中阿肯色大学的卡伦·斯蒂尔曼和凯尔·费林以及费耶特维尔阿肯色大学的杰里·金博士将研究使用超临界流体去除考古文物上的有机污染。这将进一步发展非破坏性放射性碳测年方法。所进行的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，并加强与全球考古学家的合作。当一件考古文物进行放射性碳定年时，它通常会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合物；(2)将碳转化为可测量的形式；(3)测定14C测定年龄。步骤1和2最广泛使用的方法是酸-碱-酸处理（ABA），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从工件表面非破坏性地收集微量碳的能力。需要一种同样非侵入性的预处理方法来去除有机污染也是必不可少的。超临界流体萃取，特别是使用二氧化碳（scCO2）的超临界流体萃取，与传统的溶剂萃取相比，具有清洁的优点，没有表面张力效应，可以最大限度地减少处理样品的变形，并且在材料中迅速扩散。通过控制压力和温度，可以调整流体的溶剂化强度，以优先溶解工件表面和整个材料吸收的不同污染物。scCO2萃取和等离子体氧化的结合使用有可能解决考古学家在研究稀有、独特或神圣物品时面临的一个主要问题——将文物放置在一个安全的年代背景下的需求，往往被不愿破坏的愿望所抵消，即使是很小的一部分，也必须用现有的测年方法去除燃烧。此外，通过探索放射性碳测年的非传统化学预处理，将对各种基质中有机物的分离有更深入的了解。本提案中概述的最初项目将提供一个知识库，以应用于今后的研究，例如文物的保护或清洁以及从美洲土著物品上清除农药以便遣返。研究人员实验室的本科生将从接触这些先进技术和研究中受益。在阿肯色州推广科学和考古对于培养这些领域的专业人才至关重要，尤其是在一所大约18%的学生来自人均收入最低的四分之一县和该州历史上萧条的密西西比三角洲地区的大学里。需要更多对将化学知识应用于考古和文化应用感兴趣的科学家。

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.