GC-MS Analysis of Aqaba Amphora (Ras el Sheikh Humaid, wreck)

The results show in general a poor preservation of organic residues and the presence of unspecific fatty acids.Within the framework of the research project "The Content of Roman, Late Antique/Early Medieval Amphorae as Proxy of Economic Change and the Emergence of New Socio-Economic Networks" (see https://www.geschkult.fu-berlin.de/e/klassarch/forschung/projekte/late-antique---early-medieval-amphorae/index.html) a sample of Aqaba Amphora (Raith et al. 2013) from a wreck located at Ras el Sheikh Humaid and preserved in the National Museum of Riad (see Reinfeld – Held 2020) has been analysed at the Laboratory for Classical and Supramolecular Mass Spectrometry, BioSupraMol, Faculty of Biology, Chemistry and Pharmacy of the Freie Univ. Berlin using GC-MS techniques in order to identify organic residues entrapped in the ceramic and shed new light on its content. M. Reinfeld – W. Held, From Try Dive to a Wreck Documentation. Archaeological Research and Capacity Building in Saudi Arabia, in: J. A. Rodrigues – A. Traviglia (Hrsg.), IKUWA 3. Shared Heritage: Proceedings of the Sixth International Congress for Underwater Archaeology (Oxford 2020), 163-171 M. M. Raith – R. Hoffbauer – H. Euler – P. A. Yule – K. Damgaard, The View from Ẓafār – An Archaeometric Study of the ʻAqaba Pottery Complex and its Distribution in the 1st Millenium CE, Zeitschrift für Orient-Archäologie 6, 2013, 320-350.In the last twenty-five years, analytical organic chemical techniques have been developed for the chemical characterization of organic compounds absorbed in archaeological ceramics (Evershed 1993; Evershed 2008b). Gas Chromatography coupled with mass spectrometry (GC-MS) allows separating and identifying the amorphous or invisible biomolecular components of organic materials or of the natural products that contribute to the formation of a residue (Evershed 2008a). Sherd was first surface-cleaned in order to remove exogenous contamination and a total about 2 g of the powdered sample was extracted using the extraction methods described by Pecci et al. (2013 and 2013a), including the derivatization with BSTFA before analysis by GC-MS. To analyse the oil derivatives, the respective amount of powdered sample was extracted twice using 50 ml CHCl3/MeOH for 15 min, assisted by ultrasonification. The extract was separated from the solid using a centrifuge (10 min). The supernatants’ solvent was removed using a gentle stream of nitrogen. Then alkaline hydrolysis was carried out by addition of 2 mL NaOH (2M in MeOH) for 1 h at 70°C. After cooling the reaction mixture to room temperature, the sample was acidified by addition of 15 droplets of concentrated HCl in water; the pH was tested to be 1. The acidified solution was extracted twice using 3 mL CHCl3 each. After removal of the solvent, using a gentle flow of nitrogen, the extract was transferred into the sample vial using two times 50 uL CHCl3. Again, the solvent was removed. Derivatisation was carried out using 25 uL BSTFA for 1 h at 70°C. After adding 50 uL n-hexane and 25 uL internal standard solution (1.3 mg/mL dotriacontane in hexane), the sample was submitted to GC-MS analysis. The GC-MS method described in the literature was customized for an Agilent 5977E MSD single-quadrupole mass spectrometer with a 7820A GC system, equipped with a SiO2 DB-5MS GC column (30m x 0.25mm, Agilent Technologies). The instrument included an industry-standard temperature program (1 min at 50°C, then a ramp of 5°C/min, 10 min at 300°C), which utilizes Dotriacontane to mark the end of the chromatogram and as an internal standard. All of the compounds identified were compared to the retention times and mass spectra of standards produced from pure compounds, derivatised using BSTFA. Charters S., R.P. Evershed, L.J. Goad, P.W. Blinkhorn, and V. Denham 1993. "Quantification and distribution of lipid in archaeological ceramics: implications for sampling potsherds for organic residue analysis and classification of vessel use.” Archaeometry 35: 211-223. Dudd S. N., R.P., Evershed, and A.M. Gibson 1999. "Evidence for varying patterns of exploitation of animal products in different prehistoric pottery traditions based on lipids preserved in surface and absorbed residues.” Journal of Archaeological Science 26: 1473–1482. Evershed, R. P., 1993. “Biomolecular archaeology and lipids.” World Archaeology 25: 74–93. 2008a. “Experimental approaches to the interpretation of absorbed organic residues in archaeological ceramics.” World Archaeology 40: 26–47. 2008b. “Organic Residue Analysis in Archaeology: The Archaeological Biomarker Revolution.” Archaeometry 50.6: 895–924. Pecci, A., Cau Ontiveros, M. A. and Garnier, N. 2013a. Identifying Wine and Oil Production: Analysis of Residues from Roman and Late Antique Plastered Vats. Journal of Archaeological Science 40: 4491–4498. Pecci, A., Giorgi, G., Salvini, L. and Cau Ontiveros, M. A. 2013b. Identifying Wine Markers in Ceramics and Plasters Using Gas Chromatography – Mass Spectrometry. Experimental and Archaeological Materials. Journal of Archaeological Science 40, 1: 109–115