Compound-Specific Stable Isotope Analysis (CSIA)

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

Tips for CSIA of PAHs

Sample preparation
We recommend shipping samples dry; shipment of solvents requires shipment as dangerous goods and incurs additional shipping fees. If shipping samples in solvent, please do not overtighten your vial caps. We have received vials that leaked because caps were over-tightened. Turn caps until snug, but not so far that septa start to pucker.

We recommend using an internal standard if you intend to account for extraction efficiency in concentration data. Please avoid the use of small chain FAMEs as internal standards, as we often use these compounds as internal standards for calibration of isotope-ratio measurements.

Please inspect your data. While we provide the identification of the 16 priority PAHs, we also report data for all detectable, yet unidentified, peaks. This allows you to decide which data to keep and which ones to discard, rather than us performing this step for you. Very small peaks (< 1 V-s) may have biased values that should be ignored, especially when closely eluting to much larger peaks. Further, when large peaks are not fully resolved, the δ13C or δ2H measurement for each approaches the average of the two peaks. This is because the IRMS measurements take place on the combustion/pyrolysis products (CO2/H2) following chromatography and cannot fully discern the CO2/H2 from either peak.

Quality Assurance
Every SIF data report contains results for a range of calibrated quality assessment reference materials that are co-measured with each project. However, as for all analyses, we recommend that clients submit a quality assurance material to allow for their own monitoring of batch-to-batch variation over time and consider the submission of sample duplicates [1]. Ideally, these materials should be similar to the sample materials you intend to measure. Requirements for material preparation are the same as those for all sample materials.

Scheduling
The queue for CSIA at the SIF often extends several months. We recommend that you contact us about your sample submission as early as possible to expedite the analysis of your project.

References
[1] Analytical error in stable isotope ecology. 2005. T.D. Jardine, R.A. Cunjak. Oecologia 144: 528-533. doi:10.1007/s00442-005-0013-8