title: High-precision, automated stable isotope analysis of atmospheric methane and carbon dioxide using continuous-flow isotope-ratio mass spectrometry.
abstract: Small-scale developments have been made to an off-the-shelf continuous-flow gas chromatography/isotope-ratio mass spectrometry (CF-GC/IRMS) system to allow high-precision isotopic analysis of methane (CH(4)) and carbon dioxide (CO(2)) at ambient concentrations. The repeatability (1sigma) obtainable with this system is 0.05 per thousand for delta(13)C of CH(4), 0.03 per thousand for delta(13)C of CO(2), and 0.05 per thousand for delta(18)O of CO(2) for ten consecutive analyses of a standard tank. An automated inlet system, which allows diurnal studies of CO(2) and CH(4) isotopes, is also described. The improved precision for CH(4) analysis was achieved with the use of a palladium powder on quartz wool catalyst in the combustion furnace, which increased the efficiency of oxidation of CH(4) to CO(2). The automated inlet further improved the precision for both CH(4) and CO(2) analysis by keeping the routine constant. The method described provides a fast turn-around in samples, with accurate, reproducible results, and would allow a long-term continuous record of CH(4) or CO(2) isotopes at a site to be made, providing information about changing sources of the gases both seasonally and interannually.
authors.affiliation: Department of Geology, Royal Holloway, University of London, Egham, UK. r.fisher@gl.rhul.ac.uk
authors.forename: Rebecca
authors.initials: R
authors.lastname: Fisher
authors.forename: David
authors.initials: D
authors.lastname: Lowry
authors.forename: Owen
authors.initials: O
authors.lastname: Wilkin
authors.forename: Srimathy
authors.initials: S
authors.lastname: Sriskantharajah
authors.forename: Euan G
authors.initials: EG
authors.lastname: Nisbet
mesh_terms: D000397:Air Pollution / Q000032:analysis*; D001272:Atmosphere / Q000032:analysis*; D002245:Carbon Dioxide / Q000032:analysis*; D002250:Carbon Radioisotopes; D004784:Environmental Monitoring / Q000295:instrumentation / Q000379:methods; D004867:Equipment Design; D019544:Equipment Failure Analysis; D017022:Flow Injection Analysis / Q000295:instrumentation* / Q000379:methods; D008401:Gas Chromatography-Mass Spectrometry / Q000295:instrumentation* / Q000379:methods; D008697:Methane / Q000032:analysis*; D015203:Reproducibility of Results; D012371:Robotics / Q000295:instrumentation* / Q000379:methods; D012680:Sensitivity and Specificity
chemical_list: D002250:Carbon Radioisotopes; D002245:Carbon Dioxide; D008697:Methane