A new approach for the investigation of ancient silver coins: depth profile analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)

International audienceLaser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is a powerful analytical technique that is successfully used in many fields for the analysis of solid samples. The number of elements that can be determined and the swiftness of the analysis are the main advantages of this technique. It also allows permits collection of concentration profiles as the penetration of the laser in the sample is progressive. It is this specificity that has been specially exploited in this study to apply LA-ICP-MS to ancient silver coins. These coins are often covered by a silver surface enrichment layer that has to be discarded. LA-ICP-MS concentration profile is the perfect tool to achieve this: the profiles allows a visualization of the variation of concentration as the laser penetrates the sample, so it is possible to determine the composition of the alloy that has not been disturbed by surface enrichment phenomena. The major elements (Ag and Cu) and five main minor elements (Zn, Sn, Au, Pb, Bi) are analyzed by this way, whereas the minor and trace elements are determined as an average on the entire ablation. The most suitable analytical parameters have been defined. The reliability of the protocol developed has been verified by a comparison with Fast Neutron Activation Analysis, proving the relevance of the LA-ICP-MS analysis of silver coins. Carolingian coins have been analyzed for this study. This coinage was relevant as it was suitable for the development of the LA-ICP-MS analytical protocol and for a better understanding of early medieval economy. Some preliminary results on this topic are presented here