Mathieu,

I don't think that NaOH is an option, considering the relatively high solubility of Na2CO3 you will not precipitate much (any) of the low DIC in precipitation.

Samuel 

-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Mathieu Daëron
Sent: woensdag 18 mei 2016 14:49
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] DIC precipitation by addition of barium hydroxide

Thanks for the feedback, Samuel.

Point taken. Am I right that all of the issues you raise also apply to NaOH, except that NaHCO3 is more soluble, so that you need less volume of it to raise the pH (and you may have a higher concentration of DIC in the liquid phase of your NaOH solution)?

- Mathieu


> On May 18, 2016, at 11:39, Samuel Bodé wrote:
> 
> 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 ?