Carbonate

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 Apatite/Carbonate by GasBench-IRMS

The SIF provides δ13C and/or δ18O analysis of powdered apatite and biogenic carbonate samples using a GasBench II system interfaced to a Delta V Plus IRMS (Thermo Scientific, Bremen, Germany).

Analysis of 13C and 18O in apatite/biogenic carbonate

Powdered biogenic carbonate and apatite samples are dried at 60 °C in a drying oven overnight.  The SIF does not accept geological carbonate samples.  Apatite is weighed at 1 mg (biogenic carbonate at 0.1 mg) into 4.5-mL Labco Exetainer vials and capped. Vials are loaded into an autosampler rack held at 30 °C and flush/filled with helium at 100 ml/min for 10-min using a CTC PAL autosampler device. Several drops of phosphoric acid (103 %) are manually injected through a septum into each vial using a syringe to liberate CO2 from carbonate, and vials are returned to the autosampler rack to equilibrate for 24 h at 30 °C. The vial headspace is analyzed for CO2 using a ThermoFisherScientific GasBench II device with a 100 µl sample loop connected to a ThermoFisherScientific Delta V Plus gas-isotope ratio mass spectrometer. A pure CO2 reference gas is used to calculate provisional delta values of the sample peak. Final delta values are obtained after adjusting the provisional values for changes in linearity and instrumental drift such that correct 13C and 18O delta values for laboratory reference materials are obtained. NBS 18 (-5.01‰, -23.01‰, for δ13C and δ18O respectively), NBS 19 (1.95‰, -2.20‰), and LSVEC (-46.60‰, -26.70‰) are used to calibrate data on the VPDB scale.

Limit of Quantitation and Long-term standard deviation for 13C and 18O in carbonate by GasBench-IRMS

13C and 18O in carbonate (as CO2) : Limit of Quantitation: approx. 150 nanomoles

                                               Long-term standard deviation: 13C, 0.1 ‰; 18O, 0.2 ‰