History

Although recent advances in analytical methods have accelerated the study of these materials, the analysis and identification of ancient organic residues has a long history. An early example, in the 1920s, was the use of wet chemical techniques by the chemist Alfred Lucas to study organic material from pottery and mummified human remains from the tomb of Tutankhamun. Over the last 20 years or so, the analysis of organic residues has grown into a recognized field in its own right. Examples of organic residues include the debris associated with the remains of food and other natural products as a result of their manipulation in pottery containers (e.g. cooking of food), the balms in the wrappings of mummified bodies and traces of colouring dyes impregnated in ancient textiles. Given the amorphous character of organic residues, the most effective approach to their identification lies in their chemical composition. Characterization of organic residues generally relies upon the principles of chemotaxon-omy, where the presence of a specific compound or distribution of compounds in an unknown sample is matched with its presence in a contemporary natural substance. The use of such molecular markers is not without its problems, since many compounds are widely distributed in a range of natural materials, and the composition of an ancient residue may have changed significantly during burial. In general, molecular markers belong to the compound class defined as the lipids, a heterogeneous group of molecules which includes fats and oils and molecules with common solubilities, such as the constituents of resins and waxes.

Early work in this field relied heavily on either thin-layer chromatography (TLC) or gas chromatog-raphy (GC) alone to characterize residues. Today, combined GC-mass spectrometry (GC-MS) and, to a lesser extent, high-performance liquid chromatog-raphy-MS (LC-MS) are demonstrating considerable value in identifying ancient organic matter. The wider availability of these techniques and, in particular, the introduction of GC-isotope ratio mass spectrometry (GC-IRMS), is contributing to more specific identifications than was possible before. GC-IRMS allows the ratios of abundances of stable isotopes of elements such as carbon and nitrogen to be determined for individual compounds introduced via a gas chromatograph. Stable isotope ratios are of particular importance to studies of foodwebs due to the characteristic isotope signatures of plants utilizing different photosynthetic pathways. These distinctive ratios are passed along the food chain to herbivores and carnivores. The method requires very small samples and is being applied to trace organic residues in pottery vessels to establish their origin with a high degree of precision.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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