The effect of matrix interferences on in situ boron isotope analysis by laser ablation multi‐collector inductively coupled plasma mass spectrometry

Abstract

Rationale: Boron isotope analysis of marine carbonates by laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) offers the potential for rapid sample throughput, and the means to examine micron scale variations in the δ¹¹B signatures of fossil skeletons and shells/tests of marine organisms. Existing studies demonstrate an acceptable level of reproducibility is achievable, but also typically show a level of accuracy outside the limits required by most applications. Here we investigate matrix interference effects as a cause of inaccuracy and imprecision.

Methods: Analyses were performed on a standard format Thermo Scientific Neptune Plus MC-ICP mass spectrometer coupled to a New Wave Research 193nm ArF laser ablation system. The effects of matrix interference on δ¹¹B analysis were investigated through analyses of a set of reference materials with differing B/Ca ratios. Three approaches to correct for matrix-induced effects were trialled: 1) use of matrix-matched standards, 2) utilising the relationship between δ¹¹B inaccuracy and ¹¹B/⁴³Ca, ¹¹B/⁴⁰ArCa⁴⁺ or ¹¹B/Ca_interference from three reference materials with known δ¹¹B values and varying B/Ca ratios, and 3) direct characterisation of the (sloping) interference itself.

Results: Matrix interference from scattered Ca ions on ¹⁰B can impede both the accuracy and reproducibility of δ¹¹B analysis by LA-MC-ICP-MS. Based on analyses of two in-house reference materials, deep sea coral PS69/318-1 and inorganic calcite UWC-1, we find approach 2, following the ¹¹B/Ca_interference relationship, gives the best mean accuracies (within 0.4‰ of solution values) and external reproducibilities (± 0.5‰ 2 SD for PS69/318-1). This approach has been applied to analyses of an annual growth cycle of a Siderastrea siderea coral and eight Cibicidoides wuellerstorfi benthic foraminifera. Both coral and foraminifera data match solution MC-ICP-MS analyses within reported uncertainties.
Conclusions: LA-MC-ICP-MS can produce accurate and precise δ¹¹B data to a 0.5‰ (2σ) level on <0.3 ng B after correction for Ca interference effects.

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Identifiers

ORCID for Christopher David Standish: orcid.org/0000-0002-9726-295X

ORCID for Thomas Chalk: orcid.org/0000-0002-2880-3847

ORCID for Tali Babila: orcid.org/0000-0001-9948-9341

ORCID for James Milton: orcid.org/0000-0003-4245-5532

ORCID for Gavin Foster: orcid.org/0000-0003-3688-9668

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