Russian scientists use a mass spectrometer to look inside an ancient Greek amphora
Russian scientists have identified the components of the oldest bitumen sample to be found in an ancient vase and made an accurate estimate of its age. In their article in the Journal of Mass Spectrometry, the researchers from the Moscow Institute of Physics and Technology (MIPT), the Skolkovo Institute of Science and Technology (Skoltech), the Institute for the History of Material Culture, the Talrose Institute for Energy Problems of Chemical Physics, and the Emanuel Institute of Biochemical Physics of the Russian Academy of Sciences (IBCP RAS) propose a new and more effective approach to organic compound analysis and introduce specially designed software.
Amphora contents analysis. Source: MIPT press-office
Bitumen is a form of petroleum found in natural deposits. Its use dates back to the Stone Age. The word ‘mummy’, for example, derives from the Persian ‘mūm’, or ‘bitumen’, because this substance was used in embalming. The Greeks used bitumen in construction, medicine, and warfare—it is possible that the legendary ‘Greek fire’ was based on bitumen. The oldest amphora filled with bitumen (5ᵗʰ century BCE) was discovered by Russian archaeologists on the Taman Peninsula, a highly volcanically active region (numerous petroleum seeps are located there) and a possible source of the bitumen imported by the Greeks.
It is possible the ancient weapon known as ‘Greek fire’ was based on bitumen (public domain)
More oxygen as time goes by
The analysis of ancient bitumen samples can reveal their age and origin. US researchers have used a mummy to demonstrate that ancient Egyptian bitumen did not come exclusively from the Dead Sea. If the age of the bitumen sample from the amphora is indeed close to 2,500 years, this implies a prolonged period of biodegradation due to the activity of bacteria, causing oxidation of the organic molecules in bitumen, i.e. the gradual introduction of additional oxygen into the sample. This means that older samples contain more oxygen atoms.
Elemental analysis of the Taman sample indicated an oxygen (O) content of 11%, as opposed to 1% or less in fresh petroleum samples, with the other elements—carbon (C), hydrogen (H), nitrogen (N), and sulfur (S)—present in the normal amounts. This indicates that the sample had been degrading for a long time within the amphora; apparently it had been there for 2,500 years. However, elemental analysis does not identify the kinds of molecules present in the sample. To do this, the researchers used ultrahigh-resolution mass spectrometry.
The Greek amphora analysed in the study. Source: MIPT press-office
Mass spectrometry is an analytical technique that sorts charged particles in an electric and/or magnetic field based on their mass-to-charge ratio (m/z). A mass spectrum is a pattern of peaks, each corresponding to an ion with a specific mass-to-charge ratio. It enables the identification of the constituent substances in the sample.
A closer look
Distinguishing the numerous peaks in the mass spectra of bitumen from one another is a challenge. To do this, the researchers utilised the advanced ultrahigh-resolution mass spectrometry techniques developed at the laboratory, which allowed them to distinguish molecules whose masses differ only by a fraction of that of an electron. This meant that not one of the individual components in the bitumen sample—and there are tens of thousands of them—escaped their attention. They also determined the elemental composition of the constituents. The analysis revealed that among substances in the Taman bitumen sample that contain oxygen, most have four to nine oxygen (O) atoms. Samples of ordinary petroleum, however, contain numerous compounds with two oxygen atoms and very few of those with three or four oxygen atoms. Exposing petroleum to ozone (O₃) leads to oxidation and lends substances with an oxygen content similar to that of the bitumen from the amphora, which supports the theory that the Taman sample bears the effect of prolonged oxidation.
One of the researchers holding the Greek amphora. Source: MIPT press-office
The research supervisor of this work is Professor Evgeny Nikolaev, scientific heads MIPT’s Laboratory of Ion and Molecular Physics, the same name lab at the Institute of Energy Problems of Chemical Physics (of the Russian Academy of Sciences) and the Laboratory of Mass Spectrometry at Skoltech Space Centre. He and Yuri Kostyukevich postdoctoral researcher at Skoltech, who performed main experiments in this project, shared his perspective on the discovery:
“Ultrahigh-resolution mass spectrometry is an immensely powerful technique in analytical chemistry. Applied to petrochemistry, archaeology, and medicine it provides a valuable insight into the molecular composition of a substance. The analysis of ancient bitumen has already revealed much about the transformations that petroleum undergoes over the course of millennia. Thanks to mass spectrometry, we might be able to obtain new information about the goods traffic and trade routes in the ancient world.”
Top image: The Greek amphora analysed in the study. Source: MIPT press-office
Journal Reference: Yury Kostyukevich, Sergey Solovyov, Alexey Kononikhin, Igor Popov, Eugene Nikolaev. The investigation of the bitumen from ancient Greek amphora using FT ICR MS, H/D exchange and novel spectrum reduction approach.. Journal of Mass Spectrometry, 2016; 51 (6): 430 DOI: 10.1002/jms.3769