Droplet probe: A non-destructive residue analysis of Wari ceramics from the imperial heartland

Abstract

Analyzing ceramics from ancient cultures, many of which are degraded or damaged from hundreds or thousands of years of weathering, present some unique challenges. Mass spectrometry coupled with separation techniques, such as liquid chromatography, provides a means to analyze residues on artifacts. However, most well-known analytical techniques usually cause at least some amount of destruction of the material during the preparation phase, leading to the loss of valuable spatial information and possibly hampering future analyses. In this study of ancient Andean sherds, we present a test case of using a non-destructive LC-MS technique, termed the droplet-liquid microjunction-surface sampling probe (i.e., droplet probe), for studying the chemistry of residues on ceramics. This method combines the benefits of mass spectrometry with the collection of chromatographic data, the combination of which affords a wealth of data. Three naturally occurring plant secondary metabolites, aurantiamide acetate (1), aurantiamide benzoate (2), and aurantiamide (3) were identified on the surface of a vessel and a spoon sherd from the central highlands of Peru. Fragmentation patterns, mass defect filtering and comparison to an in-house standard were used to further confirm the identification of these metabolites. The droplet probe allows for the identification of the chemistry of residues on archeological materials, and in turn, such data allow inferences regarding the potential original or final use of these artifacts.