Aw Stott

New chromatographic, mass spectrometric and stable isotope approaches to the classification of degraded animal fats preserved in archaeological pottery

A new method is described for distinguishing between animal fats preserved in ancient pottery. Analysis of lipid fractions from two morphologically distinct vessel types (lamps and dripping dishes) using on-line gas chromatography- 13 combustion-isotope ratio mass spectrometry (GC-C-IRMS) showed that they could be distinguished by plotting thed C 13 value for n-hexadecanoic acid against that for n-octadecanoic acid. The d C values obtained for modern reference fats from domesticated animals likely to have been important in antiquity showed the lamp extracts to correlate with ruminant animal 13 fat, such as sheep or cattle, whereas the dripping dishes had d C values similar to those of non-ruminant animal fat, such as pig. These findings were entirely consistent with distributional information obtained by GC and with positional isomer information gained from analysis of dimethyldisulphide derivatives of the monounsaturated fatty acids. The results indicate that GC-C-IRMS has considerable potential for the classification of animal fats absorbed in ancient pottery particularly 13 where fatty acid distributions have been altered by degradation during vessel use or burial. d C values were also shown to be of value in detecting the use of vessels in the processing of animal products from more than one source.

New Criteria for the Identification of Animal Fats Preserved in Archaeological Pottery

R.P. Evershed, H.R. Mottram, S.N. Dudd, S. Charters, A.W. Stott,G.J. LawrenceOrganic Geochemistry Unit, School of Chemistry, Cantock’s Close,University of Bristol, Bristol, BS8 1TS, UKA.M. GibsonClwyd-Powys Archaeological Trust, 7a Church Street, Welshpool Powys,SY21 7DL, UKA. ConnerCambridgeshire County Council Archaeology Unit, Fulbourne CommunityCentre, Haggis Gap, Fulbourne, Cambridge, CB1 5HD, UKP.W. BlinkhornOxford Archaeological Unit, Janus House, Osney Mead, Oxford, OX2 0ES, UKV. ReevesCentral Archaeological Services, English Heritage, Fort Cumberland,Fort Cumberland Road, Eastney, Portsmouth, PO4 9LD, UK

Formation of long-chain ketones in ancient pottery vessels by pyrolysis of acyl lipids

Abstract Structural and Isotopic (δ 13 C) evidence indicates the formation of series of long-chain ketones in archaeological pottery can occur by condensation of long-chain carboxylic acids. The formation of the ketones is confirmed by pyrolysis of free fatty acids or triacylglyecrols in the presence of fired clay matrix.

Formation of long-chain ketones in archaeological pottery vessels by pyrolysis of acyl lipids

Abstract Studies of organic residues preserved in unglazed archaeological pottery have revealed the presence of homologous series of long-chain ketones containing 29–35 carbon atoms. The C31, C33 and C35 ketones are particularly abundant and exhibit a distinct monomidal distribution. The presence of long-chain ketones in potsherds is usually ascribed to the absorption of epicuticular waxes into the pottery fabric during the cooking of leafy vegetables. However, compound specific stable carbon isotope (δ13C) analyses of the individual lipids present in the potsherd extracts, in combination with detailed structural information, indicates that these ketones do not derive from plant waxes. Isotopic and structural analysis of the fatty acids, which always co-occur with the ketones, suggest that a precursor-product relationship exists. Micro-scale pyrolysis of a range of free fatty acids and triacylglycerols in the presence of various inorganic matrices was undertaken in exploring the possibility of an abiological route to the formation of the ketones. Depending on the pyrolysis conditions employed, substantial yields of long mid-chain ketones were formed which were structurally and isotopically congruent to those observed in the ancient potsherds. The ketones are formed by ketonic decarboxylation (a type of head to head condensation reaction), probably involving fatty acid metal salts as intermediates, the metal being provided by the inorganic matrix. Apart from the abundant long mid-chain ketones various other products such as methylketones, methyl esters, alkanes, alk-1-enes and homologous series of minor ketones are formed as secondary pyrolysis products. These latter products are not found in the pottery probably due to less vigorous thermal conditions achieved during the original use of the vessel compared with those attained in the laboratory pyrolysis experiments. Evidence for this comes from the formation of the fatty acid methyl esters which are only produced under the most forcing of pyrolysis conditions.

Monitoring the routing of dietary and biosynthesised lipids through compound--specific stable isotope (delta 13C) measurements at natural abundance.

mother’s cousins’ grand-offspring of the workers [13, 14]. This hardly suggests that the wasps will be unwilling to rear brood of different levels of relatedness. The most likely explanation for our results is therefore that cofoundresses forced to nest alone are incapable of rearing as much brood as queens forced to nest alone or a solitary foundress, and hence we suggestion that wasps may choose their nesting strategies based on their broodrearing abilities.

Direct dating of pottery from its organic residues: new precision using compound-specific carbon isotopes

Techniques for identifying organic residues in pottery have been refined over the years by Professor Evershed and his colleagues. Here they address the problem of radiocarbon dating these residues by accelerator mass spectrometry (AMS) which in turn dates the use of the pot. Fatty acids from carcass and dairy products cooked in the pot were isolated from early Neolithic carinated bowls found at the Sweet Track, Somerset Levels, England, and then dated by AMS. The results were very consistent and gave an excellent match to the dendrochronological date of the trackway. The method has wide potential for the precise dating of pottery use on sites.

Chitin in the fossil record: Identification and quantification of D-glucosamine

Abstract Although a labile molecule, chitin is resistant to decay when complexed with protein. Currently, qualitative evidence for the preservation of chitin rests upon characteristic marker compounds derived through pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) of fossil arthropod cuticles, supported by a non-specific carbohydrate assay. However, unambiguous confirmation of the survival of chitin polymer requires detection of its hydrolysate monomer, d -glucosamine. We have now developed a GC–MS selected ion monitoring (SIM) method for the identification and quantification of d -glucosamine in fossil materials. Fossils of various ages and depositional settings were investigated and the results compared with those obtained by the Py–GC–MS approach. Specimens from the Rancho La Brea Tar Pits (USA, Pleistocene), showed the greatest degree of preservation: ∼10% (w/w), while fossil insects from Willershausen (Germany, Pliocene) and St Bauzile (France, Miocene) showed chitin to be present in ∼5% (w/w). Fossils from the Oligocene at Enspel, Germany, revealed that more than 0.5% is preserved for 25 million years. The GC–MS–SIM technique confirms the survival of chitin in the fossil record through the explicit identification of the polysaccharide monomer, and supports earlier Py–GC–MS and colorimetric analyses. The presence of other amino sugars of either exogenous (microbial) or diagenetic origin in more ancient specimens was also readily revealed using the GC–MS–SIM approach. This study illustrates the value of using a high-specificity quantitative ‘wet’ chemical approach in combination with Py–GC–MS to further advance the investigation of chitin in the fossil record.

Radiocarbon dating of single compounds isolated from pottery cooking vessel residues.

We have developed and demonstrated a practical methodology for dating specific compounds (and octadecanoic or stearic acid--C (sub 18:0) --in particular) from the lipid material surviving in archaeological cooking pots. Such compounds may be extracted from about 10 g of cooking potsherd, and, after derivatization, can be purified by gas chromatography. To obtain sufficient material for precise dating repetitive, accumulating, GC separation is necessary. Throughout the 6000-year period studied, and over a variety of site environments within England, dates on C (sub 18:0) show no apparent systematic error, but do have a greater variability than can be explained by the errors due to the separation chemistry and measurement process alone. This variability is as yet unexplained. Dates on C (sub 16:0) show greater variability and a systematic error of approximately 100-150 years too young, and it is possible that this is due to contamination from the burial environment. Further work should clarify this.

Compound-specific approach to the δ13C analysis of cholesterol in fossil bones

C values for cholesterol isolated from fossil animals, namely those of whales dated at 9735 + 160 yr and 75000 + 15000 yr B.P., are reported. Gas chromatography (GC) showed that 12 and 15 #g of cholesterol per gram dry weight of bone were recovered from the bones of these two fossil ani- mals, respectively. Conventional gas chromatography-mass spectrometry (GC-MS) confirmed the iden- tity of the ancient cholesterol and that the peaks separated by GC were of high purity. Gas chromatography-combustion-isotope ratio-mass spectrometry (GC--C-IRMS) of cholesterol recovered from the fossil specimens yielded 6T3C values that plotted within the range expected for the bulk fat of marine mammals. Significantly, the isotopic depletion between the cholesterol and collagen was similar for both ancient and modern whale bones, indicating reliable preservation of the 613C signal between the ancient cholesterol and the protein constituents. The potential to derive 6X3C values from individual lipids, for which the carbon skeletons are completely unaffected by decay processes, significantly extends the scope of palaeodietary studies.