Hi Mathieu,

A guess a problem might be that it is quite hard to keep the Ba(OH)2 or Ca(OH)2 from trapping CO2, of course that trapped CO2 will precipitate so if you filter just before adding, most will be discarded. However, most means, not all, so some of the formed Ca(Ba)CO3 in the stock solution will get into your sample, and as the solubility of Ba- and Ca(OH)2  is quite low, you will have to add quite large amounts of stock solution. And the added  Ca(Ba)CO3 might be substantial compared to the low DIC in the precipitation...... (you might try to compute it to see how much this would be a problem, I did not).

Can't you acidify the precipitation (H3PO4) and capture the CO2 ?
 

Samuel


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Dr. Samuel Bodé
Assistant of prof. P. Boeckx
Ghent University (UGent)
Faculty of Bioscience Engineering (FBE)
ISOTOPE BIOSCIENCE LABORATORY (ISOFYS) http://www.isofys.be/
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-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Mathieu Daëron
Sent: woensdag 18 mei 2016 11:40
To: [log in to unmask]
Subject: [ISOGEOCHEM] DIC precipitation by addition of barium hydroxide

Dear all,

A traditional method to precipitate DIC from aqueous solutions in the lab or in the field is to induce supersaturation with respect to BaCO3 by adding concentrated BaCl2 followed by NaOH (e.g., Beck et al, 2005, <https://dx.doi.org/10.1016/j.gca.2005.02.003>). However, using this method I've occasionally had issues with incorporation of Na and/or Cl in the precipitates.

Alternatively, I've considered the possibility of simply adding Ba(OH)2 (or Ca(OH)2, if I'm not worried about CaCO3 polymorphs). Does anybody have an idea why this might not work equally well?

Thanks,

- Mathieu