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 Compound Specific Analysis of 2H and 13C in n-Alkanes

Sample preparation
We recommend shipping samples dry; shipment of solvents requires handling as dangerous goods and incurs additional shipping fees. If shipping samples in solvent, please do not overtighten your vial caps. Samples leak out of vials with over-tightened caps. 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 we often use these compounds as internal standards for calibration of isotope-ratio measurements.

Please inspect your data. We provide the identification of n-alkanes, however we also report data for all detectable, yet unidentified, peaks. This allows you to decide which data to keep and which ones to discard. 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 were co-measured with the 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 QA 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 your project analysis.

Supplies

Manufacturer / Part#

Description

 Unit

National Scientific / C4000-2W

Screw-Thread Vials 9-425, 2 mL Amber with ID Patch

100/PK

National Scientific / C4000-53B

Blue Screw Caps, Red PTFE/White Silicone/Red PTFE

100/PK

National Scientific / C4010-630

Poly-spring Glass Inserts 300 µL

100/PK

National Scientific / C4012-25

Storage rack for 50 vials, polypropylene, without lid

EACH

National Scientific / C4011-25

Storage rack for 100 vials, polystyrene, with lid

EACH

Agilent / 5182-0716

Screw-Thread Vials, Large Opening, 2 mL Amber with Write-On Spot

100/PK

Agilent / 5182-0716

Screw-Thread Vials, Large Opening, 2 mL

100/PK

Agilent / 5182-0724  

Green Screw Cap, PTFE/Silicone/PTFE  

100/PK

Agilent / 5181-1270

Micro-volume Inserts, Borosilicate Glass, Conical with Polymer Support Feet

100/PK

Agilent / 5181-3377

Micro-volume Inserts, Borosilicate Glass, Flat Bottom

500/PK

Microliter / 09-1400

Conical Bottom Vials, Clear, 1.8 mL

100/PK

 

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