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Volume 10, issue 11 | Copyright
Atmos. Meas. Tech., 10, 4507-4519, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 22 Nov 2017

Research article | 22 Nov 2017

System for δ13C–CO2 and xCO2 analysis of discrete gas samples by cavity ring-down spectroscopy

Dane Dickinson1, Samuel Bodé2, and Pascal Boeckx2 Dane Dickinson et al.
  • 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 (50mL syringe) by cavity ring-down spectroscopy (CRDS). Measurements were accomplished by inletting 50mL syringed samples into an isotopic-CO2 CRDS analyser (Picarro G2131-i) between baseline readings of a reference air standard, which produced sharp peaks in the CRDS data feed. A custom software script was developed to manage the measurement process and aggregate sample data in real time. The method was successfully tested with CO2 mole fractions (xCO2) ranging from  < 0.1 to  > 20000ppm and δ13C–CO2 values from −100 up to +30000‰ in comparison to VPDB (Vienna Pee Dee Belemnite). Throughput was typically 10 samplesh−1, with 13h−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 2109ppm xCO2 and δ13C–CO2 levels varying from −27.3 to +21740‰. Repeatability tests demonstrated that method precision for 50mL samples was ca. 0.05% in xCO2 and 0.15‰ in δ13C–CO2 for CO2 compositions from 300 to 2000ppm with natural abundance 13C. 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 application for isotopic-CO2 CRDS and enhances its potential for replacing conventional isotope ratio measurement techniques. Our method involves minimal set-up 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.

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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 in other CRDS instruments.
Cavity ring-down spectroscopy (CRDS) is an increasingly popular technology for isotope analysis...