Nanosecond laser ablation – multi-collector ICP-mass spectrometry for in situ Fe isotopic analysis of micro-meteorites: application to µm-sized glassy cosmic spherules

This work evaluates the use of nanosecond laser ablation – multi-collector inductively coupled plasma-mass spectrometry (ns-LA-MC-ICP-MS) for Fe isotopic analysis of glassy cosmic spherules. Several protocols for data acquisition from the transient signals were compared, with the integration method, i.e. isotope ratios obtained by dividing the corresponding signal intensities integrated over the selected signal segment, providing the best precision. The bias caused by instrumental mass discrimination was corrected for by a combination of internal correction using Ni as an internal standard (coming from a co-nebulized standard solution) and external correction using a matrix-matched standard. Laser spot size and repetition rate were adapted to match the signal intensities for sample and standard within ± 10%. For in situ isotopic analysis, the precision of the δ56Fe values ranged between 0.02-0.11‰ (1SD, based on 4 measurement sessions, each based on ablation along 5 lines for 30s each) and 0.03-0.17‰ (SD,...