US Geological Survey, Central Energy Resources Science Center, Denver, Colorado, USA.
Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin, USA.
Rapid Commun Mass Spectrom. 2024 Jan 30;38(2):e9658. doi: 10.1002/rcm.9658.
The use of secondary ion mass spectrometry (SIMS) to perform micrometer-scale in situ carbon isotope (δ C) analyses of shells of marine microfossils called planktic foraminifers holds promise to explore calcification and ecological processes. The potential of this technique, however, cannot be realized without comparison to traditional whole-shell δ C values measured by gas source mass spectrometry (GSMS).
Paired SIMS and GSMS δ C values measured from final chamber fragments of the same shell of the planktic foraminifer Orbulina universa are compared. The SIMS-GSMS δ C differences (Δ C ) were determined via paired analysis of hydrogen peroxide-cleaned fragments of modern cultured specimens and of fossil specimens from deep-sea sediments that were either untreated, sonicated, and cleaned with hydrogen peroxide or vacuum roasted. After treatment, fragments were analyzed by a CAMECA IMS 1280 SIMS instrument and either a ThermoScientific MAT-253 or a Fisons Optima isotope ratio mass spectrometer (GSMS).
Paired analyses of cleaned fragments of cultured specimens (n = 7) yield no SIMS-GSMS δ C difference. However, paired analyses of untreated (n = 18) and cleaned (n = 12) fragments of fossil shells yield average Δ C values of 0.8‰ and 0.6‰ (±0.2‰, 2 SE), respectively, while vacuum roasting of fossil shell fragments (n = 11) removes the SIMS-GSMS δ C difference.
The noted Δ C values are most likely due to matrix effects causing sample-standard mismatch for SIMS analyses but may also be a combination of other factors such as SIMS measurement of chemically bound water. The volume of material analyzed via SIMS is ~10 times smaller than that analyzed by GSMS; hence, the extent to which these Δ C values represent differences in analyte or instrument factors remains unclear.
利用二次离子质谱（SIMS）对海洋微化石（称为浮游有孔虫）的贝壳进行微米尺度的原位碳同位素（δC）分析，有望探索钙化和生态过程。然而，如果没有与气体源质谱（GSMS）测量的传统全壳δC 值进行比较，这种技术的潜力就无法实现。
比较来自同一种浮游有孔虫 Orbulina universa 贝壳最后一个房室碎片的 SIMS 和 GSMS δC 值。通过对现代培养标本的经过氧化氢清洁的碎片和深海沉积物中化石标本的成对分析来确定 SIMS-GSMS δC 差值（ΔC）。化石标本未经处理、超声处理并用过氧化氢清洁，或真空烘烤。处理后，使用 CAMECA IMS 1280 SIMS 仪器和 ThermoScientific MAT-253 或 Fisons Optima 同位素质谱仪（GSMS）对碎片进行分析。
培养标本清洁碎片的成对分析（n=7）没有产生 SIMS-GSMS δC 差值。然而，未经处理的（n=18）和清洁的（n=12）化石贝壳碎片的成对分析分别产生平均ΔC 值为 0.8‰和 0.6‰（±0.2‰，2 SE），而真空烘烤化石贝壳碎片（n=11）则消除了 SIMS-GSMS δC 差值。
所注意到的ΔC 值很可能是由于基质效应导致 SIMS 分析中的样品-标准不匹配，但也可能是其他因素的组合，如 SIMS 对化学结合水的测量。通过 SIMS 分析的材料体积比通过 GSMS 分析的体积小约 10 倍；因此，这些ΔC 值在多大程度上代表分析物或仪器因素的差异尚不清楚。
