ABSTRACT: Standard Reference Materials (SRMs) are materials that have been thoroughly characterized and certified by NIST for properties such as elemental composition and homogeneity. These materials are used by customers in industry, academia, and other sectors, for a variety of purposes. For example, SRMs can be used for calibrations of instrumentation, validation of in-house methods, and for quality control. It is crucial that SRMs be homogenous in composition, both at the macro- and micro-scale, in order for the material to be valid. Traditionally, X-ray florescence spectroscopy (XRF) has been used for the direct elemental analysis and evaluation of homogeneity of solid samples, such as glass, ceramics, and soils. However, XRF does not provide sufficient sensitivity to detect heterogeneity in all the elements of interest it is also unable to measure beryllium, an element of interest in many materials.

A proposed complementary technique to XRF is laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The LA-ICP-MMS technique uses energy from a laser to directly interrogate a solid surface and create a plume of gas-phase particles that has the same composition as the bulk material. The gas-phase particles can then be transported to an ICP-MS for detection and quantification. The primary advantage of ICP-MS compared to XRF detection is sensitivity, which is on the order of 100 μg kg^ -1 or better for the majority of elements accessible to IC)-MS. The present SUURF project explored the effects of different experimental parameters, both within the laser and in the ICP-MS, on micro-homogeneity measurements made by LA_ICP-MS. Parameters of interest included laser beam spot size, repetition rate, ablation cell dimensions. The results indicated that optimization of experimental parameters is crucial for the successful assessment of micro-homogeneity in slid samples by LA-ICP-MS

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