On the potential of Raman-spectroscopy-based carbonate mass spectrometry

The potential for using Raman spectroscopy to measure stable oxygen isotope ratios (O/O) in carbonates is evaluated by measuring the Raman spectra and isotope ratios of a suite of 60 synthesized, O-enriched calcite crystals ranging in composition from natural abundance (0.2mole-% O) to 1.2 mole-% O.We determined the Raman-inferred isotopic ratios (RRaman) by fitting curves to the n1 symmetric stretching peak at 1086cm 1 and the smaller satellite peak, associated with the n1 stretchingmode of singly substituted carbonate groups (CO2 O) at 1065cm . The ratio of the two peak areas shows a 1:1 correspondence with the O/O ratios derived from standardmass spectrometrymethods, confirming that the relative intensities of the n1 symmetric stretching peaks is a direct measure of the isotopic ratio in the carbonates. The 1-sigma uncertainties of the RRaman values of the individual crystals were 0.00079 (384% PDB) and 0.00043 (210% PDB) for the four-crystal samplemeans. This level of uncertainty is much too high to provide significant estimates of natural variability; however, there are multiple prospects for improving the accuracy and precision of the technique. Carbon isotope ratios in carbonates cannot bemeasured by our approach, but our results highlight the potential of Raman-based isotope ratio measurement for C and other elements inminerals and organic compounds. Copyright © 2012 John Wiley & Sons, Ltd.