COMPREHENSIVE CHARACTERIZATION OF AGED LIPIDS BY USING CHROMATOGRAPHIC ANALYTICAL TECHNIQUES COUPLED TO MASS SPECTROMETRY DETECTION

1. Introduction Analytical investigations of organic residues contained in ancient pottery can address a wide range of archaeological questions and provide important clues on diet, food storage and processing, ritual and medical practices, trade and use of commodities, domestication of animals, etc. To date, lipids are the main chemical class of substances investigated in archaeological pottery. This is due to their hydrophobicity that limits their percolation and allows their persistence in the archaeological site [1]. However, the lipids may undergo chemical or microbiological degradations in situ over time. This fact further complicates the interpretations on the origin of lipid matter [2]. Therefore, determining the nature and origin of lipids in ancient pottery is a difficult task since they reflect a range of complex transformations caused by a series of alteration processes (i.e. thermal decomposition, oxidation, hydrolysis). In this regard, accelerated ageing tests can provide key elements to study the formation of characteristic compounds that could indicate unambiguous origin for the organic archaeological remains. 2. Results and Discussion Thermo-oxidative treatments were carried out in laboratory in order to simulate the natural degradation of lipid matter occurring in archaeological pottery. In detail, triglyceride standards of tristearin, triolein, trilinolein and trilinolenin were kept in an oven at 120°C for three weeks. In addition, the same ageing treatment was applied to Extra-Virgin Olive Oil (EVOO). The degradation of the aged samples was monitored weekly by using liquid and gas chromatographic techniques coupled to mass spectrometers (Figure 1). The sampling of highly volatile compounds was performed by using head-space solid-phase microextraction (HS-SPME) technique and the analyses were carried out using gas chromatography-mass spectrometry (GC-MS). Particular attention was also paid to the evaluation of oxidated fatty acid species, such as (α, ω)-dicarboxylic acid, analyzable by GC technique previous conversion to trimethyl silyl ether (TMS) derivatives. Intact lipids analysis was performed by Non-Aqueous Reversed Phase High Performance Liquid Chromatography coupled to Atmospheric Pressure Chemical Ionization Mass Spectrometry (NARP-HPLC-APCI-MS). Elution of the lipid species occurs according to increasing partition number (PN), derived from the equation PN = CN − 2DB, where CN and DB are the carbon number and double bond number of FAs in the structure. In both cases, a reliable identification was achieved combining the Linear Retention Index (LRI) system with the MS data. 3. Conclusions Thermo-oxidation products were identified in univocal manner through the use of two different identification parameters: spectral similarity and linear retention index (LRI) correspondence, both by GC and LC methods coupled with MS detection. In addition, thermo-oxidation treatment produced several volatile compounds including short-chain fatty acids (SCFAs), aldehydes, ketones, lactones, esters.