Sulfur in Solids

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

Returning SIF Samples (Facility closes July 26, 2026)

Dear Valued Client, 

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.

We regret to inform you that SIF staff will be unable to process your submitted samples before the facility's closure date. As a result, we would like to offer the option of returning your samples. If you would like your samples returned, please submit the request via return form on the SIF website.   If you do not wish to have the samples returned, please notify us, and we will arrange for their appropriate disposal in accordance with established protocols.

We sincerely appreciate your support of the Stable Isotope Facility and the opportunity to have served your research needs.

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

34S Analysis of Solid Samples

The SIF provides 34S isotope analysis of organic solid materials using an elemental analyzer and pre-concentration unit interfaced with a continuous-flow isotope-ratio mass spectrometer.

Analysis

Stable isotope ratios of 34S in solid samples are measured using an Elementar vario ISOTOPE cube interfaced to an Isoprime PrecisION IRMS (Cheadle Hume, Stockport, UK). Samples are combusted at 1000°C in a reactor packed with tungsten oxide and elemental copper. Immediately following combustion, sample gases are reduced with elemental copper at 900°C and subsequently pass through a buffering reactor filled with quartz chips held at 900°C. SO2 and CO2 are then separated by purge and trap, allowing for full separation and peak focusing. Following separation, the SO2 adsorption trap is heated and the sample SO2 passes directly to the IRMS for measurement.

During analysis, samples are interspersed with replicates of several laboratory reference materials to monitor and allow for correction of any potential variation in drift and linearity. Final 34S delta values are obtained after adjusting the provisional measurements such that correct 34S delta values for laboratory quality assurance materials are obtained. Laboratory reference materials have been calibrated directly against IAEA S-1, S-2, and S-3, as well as NBS-127, SO-5, and SO-6. The long-term reproducibility of this method is ± 0.4 ‰.

The SIF does not currently offer 34S analysis of soils or sediments.  GF/F filter material cannot be run on the sulfur instrument, please avoid/remove all particles of filter prior to sample encapsulation.