Archaeological samples

A novel technique for dating archaeological samples called ammo acid racemiza tion (AAR) IS based on the stereochemistry of ammo acids Over time the configuration at the a carbon atom of a protein s ammo acids is lost m a reaction that follows first order kinetics When the a carbon is the only chirality center this process corresponds to racemization For an ammo acid with two chirality centers changing the configuration of the a carbon from L to D gives a diastereomer In the case of isoleucme for example the diastereomer is an ammo acid not normally present m proteins called alloisoleucme... 

Some solid materials are very intractable to analysis by standard methods and cannot be easily vaporized or dissolved in common solvents. Glass, bone, dried paint, and archaeological samples are common examples. These materials would now be examined by laser ablation, a technique that produces an aerosol of particulate matter. The laser can be used in its defocused mode for surface profiling or in its focused mode for depth profiling. Interestingly, lasers can be used to vaporize even thermally labile materials through use of the matrix-assisted laser desorption ionization (MALDI) method variant. 

Saunders, S.R., Fitzgerald, C, Rogers, T., Dudar, C. and McKillop, H. 1992 A lest of several methods of skeletal age estimation using a documented archaeological sample. Journal of the Canadian Society of Forensic Sciences 25 97-118. 

Table 7.1. Collagen yield, carbon and nitrogen composition for archaeological samples. Layers are labeled O = outer, M = middle. 1 = inner,...

Tabic 7.2. Comparison o[ paLlern profiles for the different layers of partitioned archaeological samples. 

The many possible errors, as well as the difficulties inherent to the radiocarbon dating method itself, serve to emphasize the need for a close collaboration between archaeologists and natural scientists when dating archaeological samples by the radiocarbon method. 

El-Kammar, A., R. G. V. Hancock, and R. O. Allen (1989), Human bones as archaeological samples Changes due to contamination and diagenesis, in Allan, R. O. (ed.), Archaeological Chemistry, Advances in Chemistry Series, Vol. 4, American Chemical Society, Washington, DC. 

Erhardt, D. (2005), Analysis of organic archaeological samples, Abstracts of Papers, 230th ACS National Meeting, Washington, DC, August 28-September 1, 2005. 

However, in many archaeological samples pimarane diterpenoids are often absent, and of the abietane compounds only dehydroabietic acid remains. In fact, dehydroabietic acid is present as a minor component in the fresh resins, but its abundance increases on ageing at the expense of the abietadienic acids since the latter undergo oxidative dehydrogenation to the more stable aromatic triene, dehydroabietic acid [2,18]. If oxygen is available, dehydroabietic acid can be oxidized to 7-oxodehydroabietic acid and 15-hydroxy-7-oxodehydroabietic acid. Since these diterpenoid compounds are often the dominant components in archaeological samples [95,97], they are considered characteristic for the presence of Pinaceae resins. 

The survival of a-boswellic acid, p-boswellic acid and their O-acetates, which have been isolated only from frankincense, has been demonstrated in archaeological samples [99,107,113]. These compounds are considered as very useful specific chemical markers for the identification of frankincense in resinous archaeological materials. 

M. Regert, S. Colinart, L. Degrand, O. Decavallas, Chemical alteration and use of beeswax through time accelerated ageing tests and analysis of archaeological samples from various environmental contexts, Archaeometry, 43, 549 569 (2001). 

S. Hamm, J. Bleton, A. Tchapla, Headspace solid phase microextraction for screening for the presence of resins in Egyptian archaeological samples, Journal of Separation Science, 27,235 243 (2004). 

To summarise, a fractionation step allows the isolation of the compounds of interest from the other molecular constituents, particularly from the fatty acids that are well-ionised. To compensate for the low ionisation yield of some compounds, such as TAGs, the solutions may be doped with a cation. Samples are then directly infused into the ion electrospray source of the mass spectrometer. A first spectrum provides an overview of the main molecular compounds present in the solution based on the peaks related to molecular cations. The MS/MS experiment is then performed to elucidate the structure of each high molecular compound. Table 4.2 shows the different methods of sample preparation and analysis of nonvolatile compounds as esters and TAGs from reference beeswax, animal fats and archaeological samples. 

Archaeological sample containing well preserved TAGs from animal fats... 

Results obtained by Direct Mass Spectrometry using the Electron Ionisation Mode on Archaeological Samples and Wax Sculptures... 

Figure 4.11 Mass spectrum of an archaeological sample made of a mixture of beeswax and birch bark tar from a residue sampled on a ceramic sherd from the Iron Age site of Grand Aunay (Sarthe, France). The spectrum was obtained by Dl El MS on a GCQ Finnigan device equipped with an ion trap analyser. Adapted from Regert and Rolando, 2002 (see colour Plate 1)...

T.J. Wess, M. Drakopoulos, A. Snigirev, J. Wounters, O. Paris, P. Fratzl, M. Collins, J. Hiller, K. Nielsen, The Use of Small Angle X Ray Diffraction Studies for the Analysis of Structural Features in Archaeological Samples, Archaeometry, 43, 117 129 (2001). 

In this chapter, we first provide general considerations on the SPME process and important parameters affecting the quality of the results. In Sections 3 and 4 we present the results obtained with different reference substances and archaeological samples. 

Table 10.1 Compounds trapped by headspace SPME from different resins, gum resins and archaeological samples, presented by Increasing retention indices, with the corresponding relative peak areas (%) for each substance... 

Twenty-five archaeological samples from ancient Egypt were also analysed with the PDMS fibre, at 80°C, over 1 h [25], The samples were from the collections of the Guimet Museum in Lyon and are either balms sampled on different mummies or oils or unguents found in containers inside tombs. The best results were obtained when the samples were compact materials able to be ground just before SPME sampling. The five following examples are taken from the literature [25]. 

The archaeological sample (first to fourth century AD, sample 1286) was stocked in an amphora bearing the inscription incense in a warehouse (sector 6) at the Bir Ali site (Yemen). The authors objective was to confirm whether it really was frankincense [26]. 

SPME/GC/MS is an efficient technique to reveal the presence of resinic substances in archaeological samples. Indeed, volatile terpenes are still present in very old archaeological samples (4000 years old), particularly in the case of compact matrixes, and can be trapped by the SPME fibre. In comparison with methylene chloride extraction, SPME is very specific and allows the direct analysis of the volatile terpenes content in complex mixtures including oils, fats or waxes. For this reason, headspace SPME is the first method to use when analysing an archaeological sample it will either allow the identification of the resin or indicate further sample treatment in order to detect characteristic triterpenes. The method is not really nondestructive because it uses a little of the sample but the same sample can be used for several SPME extractions and then for other chemical treatments. 

C. Mathe, J. Connan, P. Archier, M. Mouton, C. Vieillescazes, Analysis of frankincense in archaeological samples by gas chromatography mass spectrometry, Annal. Chim., 97, 433 445 (2007). 

Passi, S., Rothschildboros, M.C., Fasella, P., Nazzaroporro, M. and Whitehouse, D. (1981) An application of high performance liquid chromatography to analysis of lipids in archaeological samples. Journal of Lipid Research 22, 778 784. 

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