Novel sampling techniques for trace element quantification in ancient copper artifacts using laser ablation inductively coupled plasma mass spectrometry

Publication date: June 2017Source:Journal of Archaeological Science, Volume 82
Author(s): Marcel Burger, Reto Glaus, Vera Hubert, Samuel van Willigen, Marie Wörle-Soares, Fabien Convertini, Philippe Lefranc, Ebbe Nielsen, Detlef Günther
Elemental analyses using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) have great potential in archaeometric research due to the quasi-nondestructive sampling and excellent sensitivity of the method. However, the application of LA-ICPMS in cultural heritage research is often limited because samples are too large to fit within an ablation cell or cannot be moved to the laboratory. This work reports the development of analytical routines that allow trace element quantification in ancient copper artifacts regardless their mobility, size or geometry.In this study, the LA sampling step was performed in ambient air using a portable laser ablation device (pLA). The LA module was placed on the object of interest and the laser-generated aerosol was either directly transferred into the ICPMS via a large-capacity gas exchange device (GED) or collected on polycarbonate membrane filters, which were later analyzed by LA-ICPMS. The analytical performances of both approaches were assessed using various copper reference materials. The laboratory-based, ablation-cell-independent pLA-GED-ICPMS method, yielded accuracies comparable to those obtained via conventional LA-ICPMS (±10%). Good performances (±30%) were also obtained with the pLA + filter sampling approach and subsequent LA-ICPMS analysis. Limits of detection for both approaches were in the low μg/g or sub- μg/g range, making these methods interesting for trace element analysis.After validating these laser-based techniques on an ancient copper object whose elemental composition had previously been determined by graphite furnace atomic absorption spectroscopy (GFAAS), five Neolithic copper artifacts found in Switzerland and France were analyzed using the pLA + filter sampling approach. A copper dagger found in Lattrigen, Switzerland was analyzed using the pLA-GED-ICPMS method. Furthermore, the laser-induced sample damage was investigated.The trace element profiles of the objects under investigation were compared to those of well-characterized copper artifacts. Thus, the chronological and cultural background of these artifacts could be determined. One group of copper artifacts showed high arsenic concentrations (up to 1% [w/w]) and could be attributed to “Mondsee copper”, which was particularly common in the eastern Alps during the Middle European Late Neolithic. Other objects under investigation showed trace element concentrations, which are typical for the Late Neolithic north of the Alps. One artifact had a composition typical for objects from the Late Neolithic of Southern France.

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