Abstract :
[en] Hafting adhesives can be seen as an indication of the cognitive and technical capabilities of the manufacturers and therefore play a key role in the debate on human evolution [1], [2]. These adhesives are mainly from plant origin (resins, gums or tar) and are often mixed with beeswax and other additives in order to make them less brittle. Archaeological evidence indicates that these adhesives were already in use in the Paleolithic from at least 120.000 years ago [3]. Discoveries for this period are however very rare and only become abundant from the Neolithic onwards [4]. Their longer exposure to biochemical alteration processes limits the chance of survival in the archaeological record. If they are present on Paleolithic stone tools, they appear often in such small quantities that they are challenging to identify by traditional gas chromatography – mass spectrometry (GC-MS) or even to remove them effectively from the stone tool. The destructive nature of traditional GC-MS analysis can damage these rare samples for other analyses. Our study aims to overcome this problem by using headspace solid phase microextraction (HS-SPME) for sample extraction and analysis by comprehensive two-dimensional gas chromatography –high-resolution time-of-flight mass spectrometry (GC×GC-HRTOFMS), which has the benefit of analyzing the volatile organic compound (VOC)s from the substance and it does not destroy the complete matrix of the adhesive.
We present the results of a pilot study intended to examine the potential of this technique for analyzing Palaeolithic adhesives. The study involved (1) an examination of experimental compound adhesives (containing pine and spruce resin, acacia gum and birch tar; beeswax and additives like charcoal, flax or ochre), (2) a blind test on experimental samples to test the reliability of the method and to determine the minimal quantity necessary for analysis, and (3) the analysis of different Palaeolithic adhesives and of experimental samples of at least 15 years old. The analysis was done on extracted and non-extracted adhesives. A unique chromatographic fingerprint was obtained for all experimental adhesive samples. The VOC profile of these adhesives proved to be extremely complex and therefore benefitted significantly from multidimensional separation techniques. GC×GC-HRTOFMS provided an optimal chromatographic separation of adhesive components. HRTOFMS data was used in order to obtain high-resolution mass spectral data to contribute to compound identification.
Our study demonstrates that GC×GC-HRTOFMS is a well suited method for identifying small quantities of compound adhesives with significant potential for Palaeolithic contexts. The additional sensitivity afforded by this technique in comparison to traditional GC-MS is a substantial benefit for these quantities. Furthermore, by only analyzing the VOCs of the adhesives, these rare archeological samples are not destroyed and can still be used for other types of analysis.
[1] L. Wadley, ‘Compound-Adhesive Manufacture as a Behavioral Proxy for Complex Cognition in the Middle Stone Age’, Curr. Anthropol., vol. 51, no. s1, pp. S111–S119, Jun. 2010.
[2] L. Barham, From Hand to Handle: The First Industrial Revolution. Oxford: Oxford University Press, 2013.
[3] P. P. A. Mazza, F. Martini, B. Sala, M. Magi, M. P. Colombini, G. Giachi, F. Landucci, C. Lemorini, F. Modugno, and E. Ribechini, ‘A new Palaeolithic discovery: tar-hafted stone tools in a European Mid-Pleistocene bone-bearing bed’, J. Archaeol. Sci., vol. 33, no. 9, pp. 1310–1318, Sep. 2006.
[4] M. Regert, ‘Investigating the history of prehistoric glues by gas chromatography-mass spectrometry.’, J. Sep. Sci., vol. 27, no. 3, pp. 244–54, Feb. 2004.
