Carbon Dioxide (CO2) in Gas

The Stable Isotope Facility (SIF) will be closing, effective July 26, 2026.

June 3, 2026
An Update on the Plant Sciences Stable Isotope Facility

Dear Faculty, Staff, Students, and Supporters,
After a lengthy review process and careful consideration, we have made the difficult decision to sunset the Stable Isotope Facility (SIF) in its current form, effective July 26, 2026.

The Department of Plant Sciences continues to face hard decisions surrounding funding allocation given the campus-wide request to reduce budgets. Over the past several years SIF has been operating with a significant and growing deficit and, despite extensive efforts over the last several months to find a solution that would allow the facility to continue to provide services to the research community, we have not found a model that is financially sustainable.

I want to thank SIF’s staff for their excellent work and dedication these past 25 years, and everyone who has played a role in supporting this facility.

We are committed to doing our best to support the researchers who rely on the facility during this transition, and will be in touch with individual clients about details of specific plans for handling existing orders over the next several weeks.

Sincerely,
Daniel Potter
Professor and Chair, Department of Plant Sciences
University of California, Davis

Original Letter

Analysis of CO2 by GasBench-IRMS

The SIF provides 13C and/or 18O analysis of CO2 in headspace vials using a Thermo Scientific GasBench interfaced to a Delta V Plus IRMS.

Analysis of 13C in Carbon Dioxide

Stable isotope ratios of carbon (δ13C) and/or oxygen (δ18O) in carbon dioxide are measured using a ThermoScientific GasBench system interfaced to a ThermoScientific Delta V Plus isotope ratio mass spectrometer (ThermoScientific, Bremen, Germany).  CO2 is sampled by a six-port rotary valve (Valco, Houston TX) with either a 100 µL, 50 µL, or 10 µL loop programmed to switch at the maximum CO2 concentration in the helium carrier gas.  The CO2 is then separated from N2O and other residual gases by a Poraplot Q GC column (25 m x 0.32 mm ID, 45 °C, 2.5 mL/min). A pure reference gas (CO2) is used to calculate provisional delta values of the sample peak.  Final 13C delta values are obtained after adjusting the provisional values for changes in linearity and instrumental drift such that correct 13C delta values for laboratory reference materials are obtained.  At least two laboratory reference materials are analyzed with every 10 samples.  Laboratory reference materials are calibrated directly against NIST 8545. Final 13C delta values, delivered to the customer, are expressed relative to the international standard V-PDB (Vienna PeeDee Belemnite)

Limit of Quantitation and Long-term standard deviation for CO2 Analysis by GasBench-IRMS

CO2 : Limit of Quantitation: approx. 150 nanomoles

           Long-term standard deviation: 0.1 ‰

Maximum measurable CO2 concentrations (without sample dilution or subsampling) is 50,000 ppm.  Actual sample measurement limits are dependent upon both gas concentration and isotopic enrichment.  Please contact us if you intend to submit 13C-enriched samples at gas concentrations more than ten times that of ambient CO2 concentration.