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SIMS Bias on Isotope Ratios in Ca‐Mg‐Fe Carbonates (Part III): δ 18 O and δ 13 C Matrix Effects Along the Magnesite–Siderite Solid‐Solution Series
Author(s) -
Śliwiński Maciej G.,
Kitajima Kouki,
Spicuzza Michael J.,
Orland Ian J.,
Ishida Akizumi,
Fournelle John H.,
Valley John W.
Publication year - 2018
Publication title -
geostandards and geoanalytical research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.037
H-Index - 73
eISSN - 1751-908X
pISSN - 1639-4488
DOI - 10.1111/ggr.12194
Subject(s) - analytical chemistry (journal) , magnesite , chemistry , calibration curve , mineralogy , isotope , calibration , fractionation , carbonate , matrix (chemical analysis) , magnesium , mathematics , environmental chemistry , physics , statistics , organic chemistry , chromatography , quantum mechanics , detection limit
This study explores the effects of cation composition on mass bias (i.e., the matrix effect), which is a major component of instrumental mass fractionation ( IMF ) in the microanalyses of δ 13 C and δ 18 O by SIMS in carbonates of the magnesite–siderite solid‐solution series (Mg CO 3 –Fe CO 3 ). A suite of twelve calibration reference materials ( RM s) was developed and documented (calibrated range: Fe# = 0.002–0.997, where Fe# = molar Fe/[Mg + Fe]), along with empirical expressions for regressing calibration data (affording residuals < 0.5‰ relative to certified reference material NIST ‐19). The calibration curves of both isotope systems are non‐linear and have, over a 2‐year period, fallen into one of two distinct but largely self‐consistent shape categories (data from ten measurement sessions), despite adherence to well‐established analytical protocols for carbonate δ 13 C and δ 18 O analyses at Wisc SIMS ( CAMECA IMS 1280). Mass bias was consistently most sensitive to changes in composition near the magnesite end‐member (Fe# 0–0.2), deviating by up to 4.5‰ (δ 13 C) and 14‰ (δ 18 O) with increasing Fe content. The cause of variability in calibration curve shapes is not well understood at present and demonstrates the importance of having available a sufficient number of well‐characterised RM s so that potential complexities of curvature can be adequately delineated and accounted for on a session‐by‐session basis.