title: Iron isotope composition of particles produced by UV-femtosecond laser ablation of natural oxides, sulfides, and carbonates.
abstract: The need for femtosecond laser ablation (fs-LA) systems coupled to MC-ICP-MS to accurately perform in situ stable isotope analyses remains an open question, because of the lack of knowledge concerning ablation-related isotopic fractionation in this regime. We report the first iron isotope analysis of size-resolved, laser-induced particles of natural magnetite, siderite, pyrrhotite, and pyrite, collected through cascade impaction, followed by analysis by solution nebulization MC-ICP-MS, as well as imaging using electron microscopy. Iron mass distributions are independent of mineralogy, and particle morphology includes both spheres and agglomerates for all ablated phases. X-ray spectroscopy shows elemental fractionation in siderite (C-rich agglomerates) and pyrrhotite/pyrite (S-rich spheres). We find an increase in (56)Fe/(54)Fe ratios of +2‰, +1.2‰, and +0.8‰ with increasing particle size for magnetite, siderite, and pyrrhotite, respectively. Fe isotope differences in size-sorted aerosols from pyrite ablation are not analytically resolvable. Experimental data are discussed using models of particles generation by Hergenröder and elemental/isotopic fractionation by Richter. We interpret the isotopic fractionation to be related to the iron condensation time scale, dependent on its saturation in the gas phase, as a function of mineral composition. Despite the isotopic variations across aerosol size fractions, total aerosol composition, as calculated from mass balance, confirms that fs-LA produces a stoichiometric sampling in terms of isotopic composition. Specifically, both elemental and isotopic fractionation are produced by particle generation processes and not by femtosecond laser-matter interactions. These results provide critical insights into the analytical requirements for laser-ablation-based stable isotope measurements of high-precision and accuracy in geological samples, including the importance of quantitative aerosol transport to the ICP.
authors.affiliation: Department of Geoscience, University of Wisconsin , 1215W Dayton Street, Madison, Wisconsin 53706, United States.
authors.forename: Francois-Xavier
authors.initials: FX
authors.lastname: d'Abzac
authors.forename: Brian L
authors.initials: BL
authors.lastname: Beard
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Czaja
authors.forename: Hiromi
authors.initials: H
authors.lastname: Konishi
authors.forename: James J
authors.initials: JJ
authors.lastname: Schauer
authors.forename: Clark M
authors.initials: CM
authors.lastname: Johnson
mesh_terms: D002254:Carbonates / Q000737:chemistry*; D007503:Iron Isotopes / Q000032:analysis; D007834:Lasers; D010087:Oxides / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry*; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D002254:Carbonates; D007503:Iron Isotopes; D010087:Oxides; D013440:Sulfides