Dissolved Organic Carbon (DOC) in Water

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

Dissolved Organic Carbon (DOC) Sample Preparation

THE SIF IS NOT CURRENTLY ACCEPTING DOC PROJECTS IN 2025.
The DOC sample preparation advice listed is for historical record.

 

For 13C of DOC

We recommend collecting 30mL of sample in 40 mL I-Chem 200 series glass vials and shipping immediately after collection. If samples need to be stored for more than a few days, collect samples in 50 mL polypropylene centrifuge tubes and freeze until ready to ship. Be sure to leave some headspace to avoid cracking the centrifuge tubes during freezing. Prior to shipping, thaw samples and transfer to I-Chem vials. If you prefer, you can send the frozen samples in centrifuge tubes and we will transfer them to I-Chem vials for an additional cost of $5.00 per sample.

Preserving Samples

To avoid changes in isotopic value or concentration after collection, samples should be sterilized to reduce biological activity. The SIF will not accept samples preserved with mercuric chloride (HgCl2) nor sodium azide (NaN3). We recommend that samples be sterilized by filtration (0.2 micron or finer media) or poisoned with zinc chloride (ZnCl2) (add 10 µl of 50% w/v ZnCl2 per milliliter of water sample).

If you are not concerned about biological activity, you may still want to filter the samples to remove particulates, as all organic carbon will be converted to CO2 during the chemical oxidation. Glass fiber filters, with a nominal pore size of 0.7um, are frequently used for this purpose.

Enriched / Tracer Experiment Samples
We do not accept DOC samples above 3700 per mil (5 atom %). For all enriched samples, please include an estimated enrichment in your sample list. Samples over 5 at% will not be analyzed.

Saline Samples

The SIF does not accept saline water samples for DOC in water at this time.  Samples up to a salinity of 20 PSU can be accepted, provided the DOC concentration is greater than 1 ppm. 

 

Supplies

Manufacturer / Part# Description Unit
IChem / S236-0040 or SB36-0040 200 series vials, 40 mL open top cap, 0.125" septum 72/PK or 144/PK
VWR / 89093-856 or 89093-870

TraceClean 40 mL vials, Processed (PC), Open-Top,

Amber or Clear

 72/PK

 

Shipping

Wrap individual glass vials to protect them during shipping. Group samples in Ziploc bags to help minimize leaking/wet boxes during shipping. Carefully package samples in an insulated box or cooler with dry ice or ice blocks. Coolers will not be returned.

Please complete and submit the online Analysis Order Form and Sample List for your samples.  Include a printed copy of these forms with your samples. The SIF uses this form to track your samples and to contact you regarding receipt of samples, data, and invoicing. For mixed analysis requests, we require the completion of a separate form for each type of analysis.

Storage and Disposal

Samples will be stored by SIF for 3 months post-analysis and then discarded. Please review your results during this 3-month window.

References

St. Jean, G. 2003. Automated quantitative and isotopic (13C) analysis of dissolved inorganic carbon and dissolved organic carbon in continuous flow using a total organic carbon analyzer. Rapid Communications in Mass Spectrometry 17: 419-428.