Comparison of different sets of external standards for the LA-ICP-MS analysis of North American copper artifacts

Abstract

Ideally, data produced by different laboratories performing the same type of analysis should be comparable. Comparability is important for exchanging data and the building of large databases in particular areas of research. Recently, the sourcing of North American copper using laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) has developed significantly prompting questions about the compatibility of the different published data sets.Several parameters affect the compositions obtained with LA-ICP-MS. The selection of external standards is used with LA-ICP-MS to convert the raw counts for each element in concentrations expressed in ppm or %wt. Ideally external standards have a composition as close as possible to that of the analyzed object. Available standard reference materials are purer than archaeological artifacts and a combination of several of them is often selected to be able to quantify all the elements of interest. LA-ICP-MS laboratories use different sets of standard reference materials based on their experience, budget and availability.This paper will compare three sets of copper standard reference materials that are used routinely to measure the composition of North American copper artifacts. It will assess how they affect the concentration measurements in that type of samples and shows that impact on the concentrations of certain elements can be significant. Too low concentrations in the standards and possible heterogeneity could be two factors explaining discrepancies.