System for δ13C-CO2 and xCO2 analysis of discrete gas samples by cavity ring-down spectroscopy
Dane Dickinson1, Samuel Bodé2, and Pascal Boeckx21Biosystems Engineering, Ghent University, Coupure Links 653, 9000 Gent, Belgium 2Isotope Bioscience Laboratory – ISOFYS, Ghent University, Coupure Links 653, 9000 Gent, Belgium
Received: 08 Mar 2017 – Accepted for review: 12 Apr 2017 – Discussion started: 20 Apr 2017
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.
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.