Dissolved Organic Carbon (DOC) Sample Preparation

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

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.