Matrix‐independent boron isotope analysis of silicate and carbonate reference materials by ultraviolet femtosecond laser ablation multi‐collector inductively coupled plasma mass spectrometry with application to the cold‐water coral Desmophyllum dianthus

Abstract

RationaleBoron isotopes are a powerful tool for pH reconstruction in marine carbonates and as a tracer for fluid–mineral interaction in geochemistry. Microanalytical approaches based on laser ablation multi‐collector inductively coupled plasma mass spectrometry (LA‐MC‐ICP‐MS) often suffer from effects induced by the sample matrix. In this study, we investigate matrix‐independent analyses of B isotopic ratios and apply this technique to cold‐water corals.MethodsWe employ a customized 193 nm femtosecond laser ablation system (Solstice, Spectra‐Physics) coupled to a MC‐ICP‐MS system (Nu Plasma II, Nu Instruments) equipped with electron multipliers for in situ measurements of B isotopic ratios (11B/10B) at the micrometric scale. We analyzed various reference materials of silicate and carbonate matrices using non‐matrix matched calibration without employing any correction. This approach was then applied to investigate defined increments in coral samples from a Chilean fjord.ResultsWe obtained accurate B isotopic ratios with a reproducibility of ±0.9‰ (2 SD) for various reference materials including silicate glasses (GOR132‐G, StHs6/80‐G, ATHO‐G and NIST SRM 612), clay (IAEA‐B‐8) and carbonate (JCp‐1) using the silicate glass NIST SRM 610 as calibration standard, which shows that neither laser‐induced nor ICP‐related matrix effects are detectable. The application to cold‐water corals (Desmophyllum dianthus) reveals minor intra‐skeleton variations in δ11B with average values between 23.01‰ and 25.86‰.ConclusionsOur instrumental set‐up provides accurate and precise B isotopic ratios independently of the sample matrix at the micrometric scale. This approach opens a wide field of application in geochemistry, including pH reconstruction in biogenic carbonates and deciphering processes related to fluid–mineral interaction.