Protocol Comparison for Organic Residue Analyses from Waterproofing Materials and Shards of Roman Archaeological Amphorae

Abstract

With the aim of addressing the impact of extractive protocols in molecular characterization of ceramic content, sixteen archaeological shards and waterproofing coatings of Roman amphorae were studied to compare the extractive capacities of protocols prevalently mentioned in wine amphorae analysis. A microwave-assisted protocol is developed in order to esterify grape-derivative markers from archaeological pitch and shard. Gas chromatography-mass spectrometry is used to highlight the great capacities of a two-step protocol that combines organic extraction with BF3-etherate complex butylation applied on archaeological shards. Instead, simultaneous alkaline fusion and direct-resin acid-catalyzed butylation are favored for the characterization of waterproofing material. The identification of tartaric acid, together with succinic, fumaric pyruvic and syringic acids provide valuable insights on the archaeological grape-derivative content, possibly wine. Diterpenic markers highlighted Pinus pitch and wood tar, originally used to waterproof the amphorae. Since markers are reliable tools in organic residue analyses, protocols exhibiting high extractive capacities are favored to avoid false conclusions drawn through the absence of markers.

Material Evidence of Sediments Recovered from Ancient Amphorae Found at the Potaissa Roman Fortress

“…Wine residue would rapidly become dry just after the amphora fragment dump disposal (e.g., Fragments 1 and 3), while the olive oil on the other amphora fragments (e.g., Fragment 2) would remain liquid for long enough to facilitate a local spillage. This scenario regarding amphora fragment dumping is sustained by the data in the literature [ 41 , 48 , 49 ].…”

“…The dominant organic volatile compound in all three samples is squalene, which confirms the sediment origins in the amphora’s ancient content. Unfortunately, squalene is reported in the literature to have a strong connection with not only wine residue [ 40 , 41 ] but also olive oil [ 42 , 43 ]. Thus, several volatile compounds such alcohol residue, such as 1-Hexadecanol and 1-Dodecanol, 2-octyl and several alkanes such astridecane, teradecane and heptadecane were found in Samples 1 and 3 which do not appear in Sample 2.…”

“…No traces of wine-related alkanes were found in Sample 2. Chassouant shows that, in Roman times, amphora fragments were deposited all together in special places [ 41 ]. Contact between different fragments might have facilitated oil spillage from several fragments onto wine amphora fragments, which would generate local contamination.…”

Archaeobotanical and chemical investigations on wine amphorae from San Felice Circeo (Italy) shed light on grape beverages at the Roman time

“…Gas chromatography-Mass spectrometry: Sample preparation and equipment. Samples of 20 mg of archaeological coatings were recovered from the internal body and bottom of the amphorae by scraping the organic layer with a scalpel and were treated following a twostep protocol [29]. The first extraction corresponds to an organic lipid extraction (labelled 1LE) while the second step is a microwave-assisted transesterification catalyzed by a Lewis acid (2LE-MW).…”

“…At the same time, analytical methods are increasingly interested in using cutting edge techniques applied to archaeological materials. Among them, liquid or gas chromatography coupled with mass spectrometry (GC-MS) dominate the field, due to highly sensitive and selective capacities to target molecules [ 21 , 25 , 27 – 29 ]. Retention time and molecular fragmentation account for trustworthy molecular identifications [ 30 ].…”