Accurate Trace Element Reporting in Corundum: Development of Secondary Ion Mass Spectrometry Relative Sensitivity Factors

Abstract

The attractive physical and chemical properties of corundum lend to this material’s importance in both its natural and synthetic forms. However, much of the quantitative work performed on this material is plagued by unknown inaccuracy as non‐matrix‐matched reference materials are used. To conduct accurate quantitative analysis using SIMS, matrix‐specific relative sensitivity factors (RSFs) were determined for eighteen trace elements in corundum using dose‐verified ion implants. The RSF values ranged from 2.56 × 1022 to 3.29 × 1024 cm‐1 with total combined uncertainty values ranging from 7 to 10%. The RSF values, which are related to ionisation potentials, showed trends consistent with expectations for an insulating oxide. The developed values were applied to calibrate reference materials for LA‐ICP‐MS and to study other natural and synthetic corundum samples. A measurement reference material calibrated for Mg, Si, Ti, V, Fe and Ga produced consistent results over ten sessions in 4 years with relative standard deviations per trace element of 5% or less, confirming the repeatability of our process. A key finding was that calibrating LA‐ICP‐MS with NIST SRM 610 and 612 glasses to analyse corundum resulted in under‐reporting trace elements Be, Ti, V, Fe, Co, Ni and Ga compared with using matrix‐matched reference materials.

Yellow Sapphire: Natural, Heat-Treated, Beryllium-Diffused, and Synthetic

“…All wafer samples were crystallographically oriented using a crystal alignment instrument with the c-axis either perpendicular or parallel to the plane of the wafer (Thomas et al, 2014). Trace element concentrations were determined either by laser ablationinductively coupled plasma-mass spectrometry (LA-ICP-MS) using the current standards at GIA in Bangkok (Stone-Sundberg et al, 2017), by secondary ion mass spectrometry (SIMS) against ion implant standards at Caltech (Stone-Sundberg et al, 2020), or by both. In addition, ultraviolet/visible/near-infrared (UV-Vis-NIR) spectra of 102 of these wafer samples were measured, from which 24 were chosen for this study of the 450 nm Fe 3+ band, as they represent equal concentration intervals of iron from most to least concentrated.…”