Contrasting matrix induced elemental fractionation in NIST SRM and rock glasses during laser ablation ICP-MS analysis at high spatial resolution

The greatest strength of the LA-ICP-MS technique is its application to microsampling in which extremely small pits are obtained. The results of this study highlight some significant different laser-induced fractionations between widely used external reference materials NIST SRM 610-614 and natural silicate reference materials (e. g., USGS reference glasses (GSE-1G, GSD-1G), MPI-DING glasses, USGS basalt glasses and zircon reference material GJ-1) at high spatial resolution analysis. For the sample matrices and analytical conditions used in this study, the laser-induced elemental fractionations for 63 selected isotopes are negligible at the spot sizes of 160-44 mu m. However, the laser-induced elemental fractionations of Li, Na, Si, K, V, Cr, Mn, Fe, Co, Ni, Cu, Rb, Cs and U (with respect to Ca) increase significantly with decreasing spot sizes from 44 mu m to 32 mu m, 24 mu m and 16 mu m in these natural silicate reference materials. Unlike in these sample matrices, laser-induced elemental fractionations of these elements in NIST SRM 610-614 are unique in that they are almost not affected by the change of spot sizes from 44 to 32 to 24 mu m, with only slight increase at the spot sizes of 16 mm. The much less significant laser-induced elemental fractionation in NIST SRM 61X in comparison with other natural silicate materials makes them not ideal as external reference materials at high spatial resolution analysis. Alternatively, this NIST SRM 61X-specific matrix effect for Li, Na, K, V, Cr, Mn, Fe, Co, Ni, Cu, Rb, Cs and U can be minimized by using Si for internal standardization. U and Pb in zircon GJ-1 are exceptions, which are zircon-specific.