Nanogram-scale boron isotope analysis through micro-distillation and Nu Plasma 3 MC-ICP-MS

• Published in: Talanta (Oxford) Vol. 269; p. 125473
• Main Authors: Rodríguez-Díaz, César Nicolás, Paredes, Eduardo, Pena, Leopoldo David, Cacho, Isabel, Pelejero, Carles, Calvo, Eva
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-03-2024
• Subjects: Boron isotopes; Marine biogenic carbonates; MC-ICP-MS; Micro-distillation; Paleo-pH; Paleo-pH; Boron isotopes; Marine biogenic carbonates; MC-ICP-MS; Micro-distillation; marine biogenic carbonates; micro-distillation; boron isotopes; paleo-pH; CBM
• ISSN: 0039-9140; 1873-3573
• DOI: 10.1016/j.talanta.2023.125473

The determination of boron isotopes (δ11B) represents a powerful tool for a variety of applications such as the reconstruction of past ocean pH and atmospheric pCO2 from the analysis of marine biogenic carbonates. In recent years, MC-ICP-MS has gained popularity over other techniques thanks to its superior sample throughput and high ionization efficiency. This study evaluates, for the first time, the performance of the Nu Instruments Plasma 3 MC-ICP-MS for measuring δ11B using different sample introduction systems and detector configurations. The main goal is to provide a detailed methodology for nanogram-scale boron isotope analysis through a straightforward approach that can be easily adopted. Boron (B) purification from the carbonate matrix was performed through micro-distillation, using a temperature of 95 °C and a minimum heating duration of 15 h, allowing the full recovery of B from up to 3 mg of carbonate mass. We attained blank values (on average 14 ± 6 pg, 1 SD, n = 27) comparable to the lowest micro-distillation blanks reported in the literature. Three sample introduction systems were tested, and the 30 μL min−1 nebuliser system outperformed the 50 and 170 μL min−1 systems in terms of signal intensity per mass of B. Two detector configurations were used based on the total boron signal intensity achieved: (1) FC11/FC12, with two Faraday cups fitted to 1011 Ω and 1012 Ω amplifier resistors to detect 11B and 10B ion beams, respectively, and (2) FC12/IC, with which we investigated, for the first time, the feasibility of combining an ion counter for detecting 10B, and a Faraday cup fitted to a 1012 Ω amplifier for 11B. The FC12/IC configuration provided accurate results compared to the use of two Faraday cups for total boron signals lower than 0.35 V (∼12 ng of B in the analysed solution). The proposed analytical procedure was validated through the analysis of several reference materials with varying boron amounts, including clam JCt-1, coral JCp-1, NIST RM 8301 Foram and Coral solutions, and boric acid ERM-AE121. Furthermore, the long-term reproducibility was assessed with two in-house standards (coral CLD-1 and foraminifera GINF-1), providing values of 25.68 ± 0.23 ‰ (2SD, n = 53; with 14–36 ng of B) and 14.90 ± 0.16 ‰ (2SD, n = 12; with 11–16 ng of B), respectively.
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•First assessment of Nu Plasma 3 MC-ICP-MS performance for δ11B analysis.•A detailed and straightforward approach for nanogram-scale δ11B analysis is provided.•Combining Faraday cup and ion counter detectors enables feasible δ11B measurements.•Microsublimation at 95 °C for ≥15 h allows boron recovery of up to 3 mg of CaCO3.•A systematic evaluation of factors determining δ11B uncertainty is presented.