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Reducing and correcting for contamination of ecosystem water stable isotopes measured by isotope ratio infrared spectroscopy

Abstract : Concern exists about the suitability of laser spectroscopic instruments for the measurement of the O-18/O-16 and H-2/H-1 values of liquid samples other than pure water. It is possible to derive erroneous isotope values due to optical interference by certain organic compounds, including some commonly present in ecosystem-derived samples such as leaf or soil waters. Here we investigated the reliability of wavelength-scanned cavity ring-down spectroscopy (CRDS) O-18/O-16 and H-2/H-1 measurements from a range of ecosystem-derived waters, through comparison with isotope ratio mass spectrometry (IRMS). We tested the residual of the spectral fit S-r calculated by the CRDS instrument as a means to quantify the difference between the CRDS and IRMS delta-values. There was very good overall agreement between the CRDS and IRMS values for both isotopes, but differences of up to 2.3 parts per thousand (delta O-18 values) and 23 parts per thousand (delta H-2 values) were observed in leaf water extracts from Citrus limon and Alnus cordata. The S-r statistic successfully detected contaminated samples. Treatment of Citrus leaf water with activated charcoal reduced, but did not eliminate, delta H-2(CRDS)-delta H-2(IRMS) linearly for the tested range of 0-20 % charcoal. The effect of distillation temperature on the degree of contamination was large, particularly for delta H-2 values but variable, resulting in positive, negative or no correlation with distillation temperature. S-r and delta(CRDS) - delta(IRMS) were highly correlated, in particular for delta H-2 values, across the range of samples that we tested, indicating the potential to use this relationship to correct the delta-values of contaminated plant water extracts. We also examined the sensitivity of the CRDS system to changes in the temperature of its operating environment. We found that temperature changes >= 4 degrees C for delta O-18 values and >= 10 degrees C for delta H-2 values resulted in errors larger than the CRDS precision for the respective isotopes and advise the use of such instruments only in sufficiently temperature-stabilised environments. Copyright (C) 2011 John Wiley & Sons, Ltd.
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Submitted on : Monday, December 2, 2019 - 2:46:33 PM
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Markus Schmidt, Kadmiel Maseyk, Céline Lett, Philippe Biron, Patricia Richard, et al.. Reducing and correcting for contamination of ecosystem water stable isotopes measured by isotope ratio infrared spectroscopy. Rapid Communications in Mass Spectrometry, Wiley, 2012, 26 (2), pp.141-153. ⟨10.1002/rcm.5317⟩. ⟨hal-02389348⟩



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