title: Automated analysis of 13C/12C ratios in CO2 and dissolved inorganic carbon for ecological and environmental applications.
abstract: Stable carbon isotope ratios (13C/12C) are a valuable tool for studying a wide range of environmental processes, including carbon cycling and subsurface microbial activity. Recent advances in automated analysis provide the opportunity to increase greatly the ease and consistency of isotopic analysis. This study evaluated an automated headspace sampler linked to a commercially available CO2 preconcentration system and continuous flow isotope ratio mass spectrometer. Field sampling and analysis methods are illustrated for delta13C of soil respired CO2, from both tracer and natural abundance experiments, and dissolved inorganic carbon from contaminated groundwater. The automated system demonstrated accuracy, precision, and linearity, with standard errors below 0.1 per thousand for replicate gas standards run at concentrations varying five-fold. It measured 40 samples per 10-hour run, with concentrations ranging from ppb to percentage levels. In the field, gas samples were injected into nitrogen-filled autosampler vials, thereby allowing use of small sample volumes, control of analyte concentration, and direct analysis by the automated system with no further preparation. A significant linear relationship between standard concentrations and peak area allows for accurate estimates of sample CO2 concentration from the mass spectrometric data. The ability to analyze multiple small-volume samples with minimal off-line preparation should enhance the application of isotopes to well-replicated field experiments for process-level studies and spatial and temporal scaling.
authors.affiliation: Lawrence Berkeley National Laboratory, Earth Sciences Division, ms 90-1116, One Cyclotron Rd, Berkeley, CA 94720, USA. mstorn@lbl.gov
authors.forename: Margaret S
authors.initials: MS
authors.lastname: Torn
authors.forename: Simon
authors.initials: S
authors.lastname: Davis
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Bird
authors.forename: M Rebecca
authors.initials: MR
authors.lastname: Shaw
authors.forename: Mark E
authors.initials: ME
authors.lastname: Conrad
mesh_terms: D000393:Air Pollutants / Q000032:analysis; D002138:Calibration; D002244:Carbon / Q000032:analysis*; D002245:Carbon Dioxide / Q000032:analysis*; D002247:Carbon Isotopes / Q000032:analysis; D002250:Carbon Radioisotopes / Q000032:analysis; D004785:Environmental Pollutants / Q000032:analysis*; D005740:Gases / Q000032:analysis; D012015:Reference Standards; D015203:Reproducibility of Results; D012987:Soil / Q000032:analysis; D014867:Water / Q000032:analysis; D014874:Water Pollutants, Chemical / Q000032:analysis; D014881:Water Supply / Q000032:analysis
chemical_list: D000393:Air Pollutants; D002247:Carbon Isotopes; D002250:Carbon Radioisotopes; D004785:Environmental Pollutants; D005740:Gases; D012987:Soil; D014874:Water Pollutants, Chemical; D014867:Water; D002245:Carbon Dioxide; D002244:Carbon