Boron isotope ratio determination in carbonates via LA-MC-ICP-MS using soda-lime glass standards as reference material

Abstract

A new in situ method using LA-MC-ICP-MS (193 nm excimer laser) for the determination of stable boron isotope ratios (δ¹¹B) in carbonates was developed. Data were acquired via a standard sample standard bracketing procedure typically providing a reproducibility of 0.5‰ (SD) for samples containing 35 ppm of boron. A single ablation interval consumed about 5 µg of sample corresponding to about 0.2 ng of boron. The major finding was the similar instrumental fractionation behaviour of carbonates, soda-lime glass and sea salt with respect to boron isotopes. As no matrix induced offset was detectable between these distinct materials we propose the use of NIST glasses as internal standards for boron isotope ratio measurements via LA-MC-ICP-MS. This finding overcomes the problem of a missing matrix matched carbonate standard for in situ boron isotope studies. As a first application a set of coral samples from a culturing experiment was analysed. δ¹¹B values range from 19.5 to 25‰ depending on the pH of the water used in the particular treatment. This is in good agreement with the results of earlier studies.