Rapid screening of pottery lipid residue profile via comprehensive two-dimensional gas chromatography

Pottery lipid residue analysis has been extensively practiced worldwide as an important part of archaeometry studies, but in some cases, the complexity of archaeological residue cannot be fully revealed by one-dimensional gas chromatography (1D GC) separation. Although the development of comprehensive two-dimensional gas chromatography (GCxGC) has offered another way to achieve better separation and higher resolution, GCxGC separation has rarely been applied to pottery residue analysis. Clearly, GCxGC separation needs to be explored to examine and scrutinize the complexity of pottery lipid residue profile as well as rapid data treatment workflow.

We analyzed pottery residue via comprehensive gas chromatography/mass spectrometry (GCxGC/MS), through which a thorough understanding and deeper insight into their constituent complexity were obtained. The merits of GCxGC/MS separation were illustrated by a structured layout of different series of compounds on a 2D contour plot, with a detailed examination of the distributions of linear and branched fatty acid methyl esters (FAMEs) congeners, dimethyl esters (DIMEs) congeners and ω-(o-alkylphenyl)alkanoic acids (APAA) congeners with similar structures. The results showed that 2D analysis increased the number of chemical signatures, especially those at a trace level, which can be favorable for fingerprinting and identification. Additionally, the ordered group featured layout in the 2D profile leads to easy and quick location and identification of compound series as well as individual compounds, together with the use of high-quality mass spectra, facilitating a more rapid and reliable identification workflow. The improved characterization of aquatic biomarkers such as APAAs provides a more detailed discussion of ancient aquatic culinary and dietary practices.

The complexity of isomerism and the number of congener patterns within pottery residues are illustrated for the first time, and 2D separation is beneficial for the analysis of pottery residues as well as other complex archaeological residues in cultural heritage and archaeological research. The 2D analysis built a visualized color plot with a structured layout of different compound series that simplified the analysis workflow, in which the archaeologist can visually compare the complexity of the sherd residue not attainable in the 1D analysis workflow. The improvement in sensitivity also enables the detection of trace-level compounds, which, in some cases, constitute key information in ancient diet studies.