Investigation of natural isotopic variation of Sb in stibnite ores via multi-collector ICP-mass spectrometry – perspectives for Sb isotopic analysis of Roman glass

Abstract

Natural variation in the isotopic composition of Sb in stibnites (Sb ores) was explored using multi-collector ICP-mass spectrometry (MC-ICP-MS). A method for isolating Sb (after acid digestion) without introducing artificial mass fractionation was developed, based on the use of a combination of cation exchange chromatography using Dowex AG50-X8 resin and anion exchange chromatography using Amberlite IRA 743 resin. For pure stibnites (Sb₂S₃), Sb isolation is not strictly required as at a 2 : 3 Sb : S molar ratio, it was demonstrated that the concomitant S does not affect the ¹²³Sb/¹²¹Sb isotope ratio result. However, the method can be deployed for other Sb ore types with a lower Sb : S ratio and for samples with lower purity. Indium was used as an internal standard for correction of the instrument-induced mass discrimination occurring in the MC-ICP-MS instrument. The ¹²³Sb/¹²¹Sb ratio could be measured with 0.002% repeatability (internal precision), while for the samples the ¹²³ε values were characterized by an uncertainty of 1 ε unit. The isotopic composition of the selected materials (stibnites from various regions of the world) shows a variation spanning 10 ε units (or 0.1%). The method developed shows potential to be used in provenance determination studies of ancient glass.