In Situ Carbon Isotope Analysis by Laser Ablation MC-ICP-MS

Abstract

Carbon isotopes have been widely used in tracing a wide variety of geological and environmental processes. The carbon isotope composition of bulk rocks and minerals was conventionally analyzed by isotope ratio mass spectrometry (IRMS), and, more recently, secondary ionization mass spectrometry (SIMS) has been widely used to determine carbon isotope composition of carbon-bearing solid materials with good spatial resolution. Here, we present a new method that couples a RESOlution S155 193 nm laser ablation system with a Nu Plasma II MC-ICP-MS, with the aim of measuring carbon isotopes in situ in carbonate minerals (i.e., calcite and aragonite). Under routine operating conditions for δC analysis, instrumental bias generally drifts by 0.8‰-2.0‰ in a typical analytical session of 2-3 h. Using a magmatic calcite as the standard, the carbon isotopic composition was determined for a suite of calcite samples with δC values in the range of -6.94‰ to 1.48‰. The obtained δC data are comparable to IRMS values. The combined standard uncertainty for magmatic calcite is <0.3‰ (1s). No significant matrix effects have been identified in calcite with the amplitude of chemical composition variation (i.e., MnO, SrO, MgO, or FeO) up to 2.5 wt %. Two modern corals were investigated using magmatic calcite as the calibration standard, and the average δC values for both corals are similar to the bulk IRMS values. Moreover, coral exhibits significant heterogeneity in carbon isotope compositions, with differences up to 4.85‰ within an individual coral. This study indicates that LA-MC-ICP-MS can serve as an appropriate method to analyze carbon isotopes of carbonate minerals in situ.

Determination of carbon isotopes in carbonates (calcite, dolomite, magnesite, and siderite) by femtosecond laser ablation multi-collector ICP-MS

“…Different types of isomorphic series of carbonate minerals were adopted in this study, including 6 dolomites (DOL-1, DOL-2, DOL-3, DOL-6, DOL-8, and DOL-9), 3 magnesites (MGS-1, MGS-2, and MGS-3) and 5 siderites (SD-1, SD-2, SD-3, SD-4, and SD-5), together with two previously characterized calcites (SXD8 and Oka153). 14…”

“…In situ C isotopic analyses by secondary ionization mass spectrometry (SIMS), 7–12 NanoSIMS 13 and laser ablation coupled to multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) 14 have received increased interest in Earth science-related studies, which provides valuable isotopic information of geological samples at a high resolution. For example, single carbonate crystallites (dolomite-ankerite) as small as 3–10 μm across can be readily analyzed by SIMS with a sub per-mil (‰) accuracy and precision (2s).…”

“…10 The micron-scale C isotope signatures of magmatic calcium carbonate (calcite) have been successfully measured using ns-LA-MC-ICP-MS with a satisfactory precision (within 0.50‰; 2SD). 14 Due to the complex chemical and physical features of natural carbonate, efforts have been made to calibrate a series of dolomite-ankerite solid solution reference materials for C isotope microanalysis using SIMS. 11 For example, a compositional bias was recorded in C isotope values for dolomite, which increased exponentially by 2.5–5.5‰ with increasing Fe contents.…”

“…11 Without exception, instrumental bias resulting from compositional dependency ( i.e. , matrix effect) remains as one of the analytical challenges for the wide application of in situ C isotope analyses for various carbonate matrices using LA-MC-ICP-MS. Chen et al (2017) successfully used nanosecond laser-Nu plasma MC-ICP-MS to determine the carbon isotope of calcium carbonate, 14 whereas the development of the carbon isotope microanalytical method of calc-magnesian, magnesian and ferruginous carbonates still remains a challenge. It is challenged by the lack of matrix-matched standards and C isotope fractionation at both the laser ablation site and ICP site.…”

Atomic Spectrometry Update – a review of advances in environmental analysis

“…Samples with a Rb/Sr ratio of <0.5 could be analysed with an accuracy of <0.0002 for One of the first LA-MC-ICP-MS carbon isotope studies of natural minerals has been reported 306 . The new method, which used an Excimer LA system coupled to an MC-ICP-MS instrument, adopted a SSB method using magmatic calcites as bracketing RMs to correct for instrumental mass bias.…”