Isotope ratio determination of objects in the field by portable laser ablation sampling and subsequent multicollector ICPMS

Abstract

Laser ablation coupled to multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) allows accurate and precise isotope ratio determination of solid samples in a quasi-nondestructive manner, making the technique interesting for isotopic provenance studies of valuable historical artifacts. In order to enable LA-MC-ICPMS analysis of objects that cannot be transported to the laboratory for analysis, a portable laser ablation sampling device was applied. Ablated material was collected on filters, which were subsequently analyzed in the laboratory by means of MC-ICPMS. Filters were analyzed by: (I) acid digestion followed by solution nebulization MC-ICPMS and (II) fast scanning filter ablation coupled to MC-ICPMS. For both procedures, the analytical performance was investigated for lead isotope ratio measurements in ceramics, lead ore (galena) and the metallic lead standard NIST SRM 981. Filter digestion followed by solution analysis allowed determination of lead isotope ratios with external precisions of better than 0.10‰. Mass-dependent deviations towards lighter isotope ratios of 0.10‰ per u were observed for metallic lead, which indicates to a low extent isotopic fractionation during the sampling procedure. Filter ablation coupled to MC-ICPMS resulted in reduced precision compared to the solution measurements. However, it enabled straightforward simultaneous isotopic and elemental analysis by splitting the carrier gas flow to a MC-ICPMS and quadrupole ICPMS. In summary, portable LA sampling followed by MC-ICPMS analysis was shown to enable lead isotope ratio determinations of objects in the field with an analytical performance similar to a laboratory-based analysis. The approach was applied to lead isotope provenancing of ancient Chinese ceramics.