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An injection method for measuring the carbon isotope content of soil carbon dioxide and soil respiration with a tunable diode laser absorption spectrometer
Author(s) -
Moyes Andrew B.,
Schauer Andrew J.,
Siegwolf Rolf T. W.,
Bowling David R.
Publication year - 2010
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.4466
Subject(s) - chemistry , analytical chemistry (journal) , carbon dioxide , soil respiration , isotope ratio mass spectrometry , absorption (acoustics) , mole fraction , flux (metallurgy) , laser , mass spectrometry , soil test , soil water , optics , environmental chemistry , chromatography , environmental science , soil science , physics , organic chemistry
We present a novel technique in which the carbon isotope ratio ( δ 13 C) of soil CO 2 is measured from small gas samples (<5 mL) injected into a stream of CO 2 ‐free air flowing into a tunable diode laser absorption spectrometer (TDL). This new method extends the dynamic range of the TDL to measure CO 2 mole fractions ranging from ambient to pure CO 2 , reduces the volume of sample required to a few mL, and does not require field deployment of the instrument. The measurement precision of samples stored for up to 60 days was 0.23‰. The new TDL method was applied with a simple gas well sampling technique to obtain and measure gas samples from shallow soil depth increments for CO 2 mole fraction and δ 13 C analysis, and subsequent determination of the δ 13 C of soil‐respired CO 2 . The method was tested using an artificial soil system containing a controlled CO 2 source and compared with an independent method using the TDL and an open soil chamber. The profile and chamber estimates of δ 13 C of an artificially produced CO 2 flux were consistent and converged to the δ 13 C of the CO 2 source at steady state, indicating the accuracy of both methods under controlled conditions. The new TDL method, in which a small pulse of sample is measured on a carrier gas stream, is analogous for the TDL technique to the development of continuous‐flow configurations for isotope ratio mass spectrometry. While the applications presented here are focused on soil CO 2 , this new TDL method could be applied in a number of situations requiring measurement of δ 13 C of CO 2 in small gas samples with ambient to high CO 2 mole fractions. Copyright © 2010 John Wiley & Sons, Ltd.