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.
We investigated the use of supercritical fluid extraction to remove absorbed soil organic matter (SOM) from archaeological artifacts prior to plasma oxidation for non-destructive radiocarbon dating. 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. In 2004, Steelman et al. showed that plasma oxidation could replace combustion as a non-destructive method for the conversion of carbon to a measurable form by accurately dating a naturally mummified infant burial from Southwest Texas. With the capability of collecting microscopic amounts of carbon from an artifact surface using plasma oxidation, a need for an equally non-intrusive pre-treatment method to remove contamination, such as humic and fulvic acids, is essential. With research conducted with funding from this award, we published a 2013 paper in the Journal of Supercritical Fluids that showed that supercritical cleaning of artifacts produces accurate radiocarbon ages on artifacts. 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. Radiocarbon dating of studied artifacts shows statistical agreement of supercritical fluid cleaned samples compared to ABA pre-treatment. Intellectual Merit 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. This project will also give a knowledge base upon which to apply to future studies, such as the conservation and cleaning of artifacts and the removal of pesticides from Native American items for repatriation. Broader Impacts Undergraduate students in the PI and co-PIs’ laboratories benefited 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/cultural applications are needed.
