Isotope signature characterization of Pb and U in open air by laser-ablation mass spectrometry

Isotope signatures have attracted growing interest in recent years. In addition to the existing mass spectrometric (MS) techniques, demand for open-air and in situ analytical tools is increasing. Laser ablation is effective in atomizing and ionizing materials, and is frequently used in MS. However, light-isotope enrichment in laser-ablated plasma plumes has to be mitigated for accurate isotope analyses. In this letter, we reported an open-air laser-ablation mass spectrometric (OA-LAMS) technique to measure isotope signatures of Pb and U samples without sample pretreatments with improved accuracy in open air. The secondary cations, PbOH⁺ and UO₂OH⁺, yielded more accurate isotope signatures regardless of environmental changes. This phenomenon was ascribed to different ionization schemes, in which the primary cations came from laser ionization of the samples and the secondary cations came from chemical ionization of the ablated neutral clusters. The results demonstrated the feasibility of the OA-LAMS method for characterizing isotope signatures.