Stable carbon isotope analyses of nanogram quantities of particulate organic carbon (pollen) with laser ablation nano combustion gas chromatography/isotope ratio mass spectrometry.

Linda Van Roij,Jelmer J Laks,Gert-Jan Reichart,Appy Sluijs

doi:10.1002/rcm.7769

Linda Van Roij, Jelmer J Laks + Show 2 more

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https://doi.org/10.1002/rcm.7769

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Abstract

RationaleAnalyses of stable carbon isotope ratios (δ 13C values) of organic and inorganic matter remains have been instrumental for much of our understanding of present and past environmental and biological processes. Until recently, the analytical window of such analyses has been limited to samples containing at least several μg of carbon.MethodsHere we present a setup combining laser ablation, nano combustion gas chromatography and isotope ratio mass spectrometry (LA/nC/GC/IRMS). A deep UV (193 nm) laser is used for optimal fragmentation of organic matter with minimum fractionation effects and an exceptionally small ablation chamber and combustion oven are used to reduce the minimum sample mass requirement compared with previous studies.ResultsAnalyses of the international IAEA CH‐7 polyethylene standard show optimal accuracy, and precision better than 0.5‰, when measuring at least 42 ng C. Application to untreated modern Eucalyptus globulus (C3 plant) and Zea mays (C4 plant) pollen grains shows a ~ 16‰ offset between these species. Within each single Z. mays pollen grain, replicate analyses show almost identical δ 13C values.ConclusionsIsotopic offsets between individual pollen grains exceed analytical uncertainties, therefore probably reflecting interspecimen variability of ~0.5–0.9‰. These promising results set the stage for investigating both δ 13C values and natural carbon isotopic variability between single specimens of a single population of all kinds of organic particles yielding tens of nanograms of carbon. © 2016 The Authors. Rapid Communications in Mass Spectrometry Published by John Wiley & Sons Ltd.

Highlights

Stable carbon isotopic ratios (δ13C values) measured on organic material are used to determine the isotopic signature of carbon sources, investigate carbon partitioning between reservoirs and investigate processes resulting in fractionation during biosynthesis
Measurements of solid organic matter δ13C values are typically based on the combustion of organic matter through an elemental analyzer (EA), after which the produced CO2 is transported by a carrier gas and measured by isotope ratio mass spectrometry (IRMS)
The stable carbon isotopic value of the CO2 contaminating the measurements, even when only minor, is essential in evaluating potential analytical offsets. This residual CO2 in our system revealed a δ13C value of À26.87 ± 0.08‰ (1σ = 0.13‰), which is close to previous observations by Moran et al.[42] (À28.64‰, 1σ = 2.61‰) and remarkably to those of Polissar et al.[28] (À27.76 ± 1.26‰), whose EA/IRMS setup is very different from the Laser ablation (LA)/IRMS systems

Summary

Introduction

Stable carbon isotopic ratios (δ13C values) measured on organic material are used to determine the isotopic signature of carbon sources, investigate carbon partitioning between reservoirs and investigate processes resulting in fractionation during biosynthesis. Since the data are skewed towards smaller standards, the intervals with small peak areas are narrower and allow for more detailed analysis around the analytical threshold of 0.85 Vs. For each interval, the mean, the offset from the accepted PE value and the standard deviation were calculated and a curve was fitted through these 25 data points (Fig. 5; Supplementary Table S3, Supporting Information).

Results

Conclusion