The possibility of overcoming spectral interferences by means of selective ion-molecule chemistry in a dynamic reaction cell (DRC) leads to an extension of the application range of ICP-MS for isotopic analysis. In this work, the effect of various instrumental parameters and the matrix composition on the mass discrimination (defined as the deviation between the experimental result and the corresponding 'true' isotopic ratio) was systematically studied. It is demonstrated that various DRC parameters-collision gas flow rate, reaction gas flow rate and bandpass settings-affect the mass discrimination. This observation is probably to be attributed to in-cell fractionation effects, occurring as a result of collisional losses, space-charge effects and kinetic effects in the ion-molecule chemistry. As the isotopic standard and the sample are always measured under identical conditions, external correction for mass discrimination assures accurate results. Under all conditions tested, internal correction for mass discrimination on the other hand-a strategy often used in Sr isotopic analysis did not provide accurate results. Also the matrix composition is demonstrated to have a significant influence on the mass discrimination, especially when using condensation product ions for isotope ratio measurement. This disadvantage can be overcome by using a matrix-matched isotopic standard for external correction or by isolation of the target element from the concomitant matrix, or at least its separation from the dominant matrix components

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Jewels and tableware made of black-appearing glass were popular in the Roman Empire. Compositional changes (due to modifications in glassmaking technology and use of raw materials) over the period considered (1 st -5 th century AD) have been investigated on a large number of samples originating from various archaeological excavations in Europe, Northern Africa and the Near East. In the course of this work, over 400 samples of Roman glass, the greatest part of them deeply coloured glass fragments, were embedded into acrylic resin and mechanically ground and polished in order to obtain flat surfaces of unaltered glass. The samples were analysed with scanning electron microscopy/energy dispersive X-ray spectroscopy and the quantification was performed by using a standard-less ZAF software. The trace elements contained in a selection of glass samples were determined via laser ablation-inductively coupled plasmamass spectrometry. The data collected in this study show that from about 150 AD a change in the black glass production process occurred, involving coloration of raw glass made with iron in the secondary workshops. Furthermore, from the 4 th century AD on we can observe a change in the type of raw glass used, while the colouring process was maintained. The main aim of this paper is to provide glass scholars with the analysis results, as reference and comparison for further studies.