δ13C of dissolved inorganic carbon

δ¹³C of Dissolved Inorganic Carbon in water samples is measured on a Gasbench II connected to a Thermo Scientific Delta V plus isotope ratio mass spectrometer or a URI-connect, Thermo Scientific Delta Ray isotope ratio infrared spectrometer in either the field or the lab. 

The analysis is done by acidifying 0.5 - 1 ml (depending on TCO₂) of water in a flushed exetainer, allowing the CO₂ to diffuse into the vial headspace. The headspace CO₂ is then purged into the analyser through the relevant inlet and compared to an internal reference gas. The samples are calibrated against internationally distributed standards. Samples are normally analyzed in triplicate.   

Samples must be collected in full glass vials with gas-tight caps. Samples must be sterilized (typically by HgCl₂ or acidification) to avoid microbial C turnover, which will alter C isotope composition, and stored refrigerated. Typically, this would be serum vials with crimp caps and HgCl₂, or preflushed 12 ml exetainers with acid in replicates (contact us for details if needed). 

Results are reported as ‰ on VPDB scale.  Normal external precision is ≤0.1 ‰ (δ¹³C) with significantly better precision achieved for many types of samples.