Analysis of DOC & DIC in Water by TIC/TOC-IRMS

The SIF provides ¹³C isotope analysis of dissolved organic C and dissolved inorganic C using a TIC/TOC analyzer system interfaced to an IRMS.

Analysis

DOC and DIC are analyzed for ¹³C using an O.I. Analytical Model 1010 TOC Analyzer (OI Analytical, College Station, TX) interfaced to a PDZ Europa 20-20 isotope ratio mass spectrometer (Sercon Ltd., Cheshire, UK). A 20-mL aliquot of sample is transferred into a heated digestion vessel and reacted sequentially with phosphoric acid then with sodium persulfate to convert DIC and DOC each into a pulse of CO₂. The two sequential CO₂ pulses liberated by the chemical treatments are carried in a helium flow to an infra-red gas analyzer (IRGA), then to the isotope ratio mass spectrometer where the ¹³C/¹²C ratios are measured and compared to ratios of laboratory standards calibrated against NIST Standard Reference Materials.

Pricing

Sample Preparation

For 13C of DOC
Filtration of water samples is recommended if they contain particulate matter, since the oxidation reaction that converts organic C to CO₂ does not distinguish between dissolved organic C and particulate organic C. A filter porosity of 0.7 micron is widely used, but you should decide what filter best suits your definition of DOC.
The SIF cannot accept water samples preserved with mercuric chloride (HgCl₂). We suggest collecting a minimum of 30mL of sample in 40 mL IChem 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 store in freezer 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 IChem vials. If you prefer, you can send the frozen samples in centrifuge tubes and we will transfer them to IChem vials for an additional cost of $1 per sample.

For 13C of DIC (and DOC)
To avoid changes in DIC concentration or isotopic value after collection, samples should be sterilized to reduce biological activity.  The SIF cannot accept water samples preserved with mercuric chloride (HgCl2).  We recommend that samples be sterilized by filtration (0.2 micron or finer media) or poisoned with sodium azide. 
Samples should be collected in 40 mL IChem 200 series glass vials. Fill vials completely with no headspace or bubbles.  Carbon dioxide will diffuse through the silicone-Teflon septa provided with the IChem vials; therefore, the septa should be replaced with low-diffusion butyl rubber septa (see Supplies below).
Refrigerate samples (do not freeze) prior to shipping and ship in insulated containers as soon as possible after collection.

For additional sample preparation information, please refer to Doctor, D.H., Kendall, C., Sebestyen S.D., Shanley, J.B, Ohte, N., and Boyer, E.W. (2007) Carbon isotope fractionation of dissolved inorganic carbon (DIC) due to outgassing of carbon dioxide from a headwater stream. Hydrological Processes. vol. 22, p. 2410-2423.

Shipping

Wrap individual glass vials to protect them during shipping. Group samples in ziplock 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.

*NEW* Please complete an Analysis Order Form and Sample List for your samples. E-mail the completed forms to sif@ucdavis.edu and include a printed copy 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 recommend completing a separate form for each type of analysis.

Contact information
UC Davis Stable Isotope Facility
Department of Plant Sciences
One Shields Avenue, Mail Stop 1
Davis, CA 95616
USA

Phone:(530) 752-8100, Fax: (530) 752-4361
E-mail: sif@ucdavis.edu

Supplies

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

Doctor, D.H., Kendall, C., Sebestyen S.D., Shanley, J.B, Ohte, N., and Boyer, E.W. (2007) Carbon isotope fractionation of dissolved inorganic carbon (DIC) due to outgassing of carbon dioxide from a headwater stream. Hydrological Processes. vol. 22, p. 2410-2423.

Tips

-Do not freeze water samples that are in glass i-Chem vials. The vials will break during freezing and your samples will be lost.

-Wrap individual glass vials with bubble wrap or foam sheet to protect during shipping. Group samples in ziplock bags to help minimize leaking/wet boxes during shipping.

-Analysis of DIC in small water samples (1-4 mL) is possible using a Trace Gas analyzer system to measure CO2 liberated from water by mixing with 1 mL 85% phosphoric acid in an exetainer vial. See “DIC in Water” for more information.

Updated September 28, 2009