Assessment of matrix effects in boron isotope analysis using 257 nm fs-LA and 193 nm ns-LA-MC-ICP-MS with new tourmaline reference materials

Abstract

This study compared boron (B) isotopic compositions of six chemically diverse tourmalines (including schorl, dravite, and elbaite types) using 257 nm femtosecond (fs) and 193 nm nanosecond (ns) laser ablation coupled with multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). Significant matrix effects were observed when non-matrix-matched standards were used, leading to δ¹¹B deviations of −0.70‰ to −0.41‰ for fs-LA and −0.63‰ to −0.57‰ for ns-LA when using dravite GIGT as a bracketing standard for schorl (TOUR1 and TOUR4) and elbaite (TOUR6). In contrast, using GIGT as the matrix-matched bracketing standard in the B analysis of dravites (TOUR2, TOUR3, and TOUR5) yielded significantly lower deviations of −0.22‰ to −0.18‰ for fs-LA and −0.44‰ to 0.12‰ for ns-LA. These findings necessitate matrix-matched standards for precise and accurate in situ measurements of B isotopes. We characterized four natural tourmaline reference materials (TOUR1, TOUR4, TOUR5, and TOUR6) for in situ B isotope analysis using LA-MC-ICP-MS and confirmed their isotopic homogeneity. The measured mean δ¹¹B values were −11.14 ± 0.40‰ (2SD, n = 597), −13.42 ± 0.57‰ (2SD, n = 509), −9.09 ± 0.60‰ (2SD, n = 486), and −8.57 ± 0.17‰ (2SD, n = 164), respectively, agreeing well with those obtained by solution nebulizer (SN)-MC-ICP-MS. Thus, schorl (TOUR1 and TOUR4), dravite (TOUR5), and elbaite (TOUR6) are recommended as candidate matrix-matched tourmaline reference materials for in situ B isotope determination.