Analytical Method Development: Comparison of Elemental and Isotopic Fractionation During Femtosecond and Nanosecond Laser Ablation

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In-situ analyses of isotopic and chemical composition are critical for documenting spatial heterogeneities within geological samples, and are now commonly accomplished by laser ablation methods. Improvements in laser technology are of current interest to the geochemical community and the potential advantages of relatively new technology has shown some growing pains but holds great promise. This award allows the researchers to evaluate the approaches needed for high-precision stable isotope analysis of major elements using new laser ablation technology by comparing two key laser ablation systems. The research will focus on iron isotopes to rigorously test issues of mass bias, the results of which can be extended to other isotope systems. Iron is also a major element that occurs in most rock-forming minerals, and so it will be of widespread interest to the geochemical community. The results will provide a basis for inter-laboratory comparisons of different methods of in situ analysis. The award will provide training and expertise for a postdoctoral fellow on the physics involved in laser ablation.This award funds the development of techniques for the high-precision stable isotope analysis of major elements using laser ablation (LA) and to compare femtosecond (fs)- vs. nanosecond (ns)-LA technologies to understand potential processes of isotopic fractionation during the ablation and ionization processes. The accuracy of fs- and ns-LA for isotopic analysis of iron isotopes will be evaluated due to known isotope heterogeneities at relevant scales. The results will be applicable to other stable isotope systems such as magnesium, silicon, and calcium, and should be extendable to radiogenic isotope systems in terms of mass bias issues associated with fs-LA and ns-LA. The specific research goals are targeted to evaluate the degree to which fs-LA is free of matrix effects and to determine what specific aspects of fs-LA appear to generate matrix free analysis as compared to ns-LA and standard solution nebulization methods. The study will be devoted to measuring the particle size distribution, chemical and isotopic composition, and morphological characteristics (e.g., agglomerates and spheroids) of aerosols generated by both fs- and ns-LA. Moreover, matrix effects will be characterized by using mineral group isotope standards (e.g., minerals such as siderite, ankerite, ferroan dolomite) and addition of elements into the LA aerosol stream by ?teeing? in the aerosol produced from a desolvating nebulizer.