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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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doi:10.5194/amt-2017-57
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
20 Apr 2017
Review status
This discussion paper is under review for the journal Atmospheric Measurement Techniques (AMT).
System for δ13C-CO2 and xCO2 analysis of discrete gas samples by cavity ring-down spectroscopy
Dane Dickinson1, Samuel Bodé2, and Pascal Boeckx2 1Biosystems Engineering, Ghent University, Coupure Links 653, 9000 Gent, Belgium
2Isotope Bioscience Laboratory – ISOFYS, Ghent University, Coupure Links 653, 9000 Gent, Belgium
Abstract. A method was devised for analysing small discrete gas samples (50 ml syringe) by cavity ring-down spectroscopy (CRDS). Measurements were accomplished by inletting 50 ml syringed samples into an isotopic-CO2 CRDS analyser (Picarro G2131-i) between baseline readings of a standard reference air, which produced sharp peaks in the CRDS data feed. A custom software script was developed to systematise measures and aggregate sample data. The method was successfully tested with CO2 mole fractions (xCO2) ranging from < 0.1 to > 20 000 ppm and δ13C-CO2 values from natural abundance up to +30 000 ‰. Throughput was typically 8 to 10 samples h−1, with 12 h−1 possible under ideal conditions. The measurement failure rate in routine use was ca. 1 %. Calibration to correct for memory effects was performed with gravimetric gas standards ranging from 0.05 to 2109 ppm xCO2 and δ13C-CO2 levels varying from −27.3 to +21 740 ‰. Repeatability tests demonstrated that method precision for 50 ml samples was ca. 0.05 % in xCO2 and 0.15 ‰ in δ13C-CO2 for normal atmospheric CO2 compositions. Long-term method consistency was tested over a 9-month period, with results showing no systematic measurement drift over time. Standardised analysis of discrete gas samples expands the scope of applications for isotopic-CO2 CRDS and enhances its potential for replacing conventional isotope ratio measurement techniques. Our method involves minimal setup costs and can be readily implemented in Picarro G2131-i and G2201-i analysers or tailored for use with other CRDS instruments and trace-gases.

Citation: Dickinson, D., Bodé, S., and Boeckx, P.: System for δ13C-CO2 and xCO2 analysis of discrete gas samples by cavity ring-down spectroscopy, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2017-57, in review, 2017.
Dane Dickinson et al.
Dane Dickinson et al.
Dane Dickinson et al.

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Short summary
Cavity ring-down spectroscopy (CRDS) is an increasingly popular technology for isotope analysis of trace-gases. However, most commercial CRDS instruments are designed for continuous gas sampling and cannot reliably measure small discrete samples. We present a novel technical adaptation that allows routine analysis of 50 ml syringed samples on an isotopic-CO2 CRDS unit. Our method offers excellent accuracy and precision, fast sample throughput, and is easily implemented to other CRDS instruments.
Cavity ring-down spectroscopy (CRDS) is an increasingly popular technology for isotope analysis...
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