Dear Juske Horita,

in an investigation of river water dissolved inorganic carbon (DIC) we 
started with the precipitation technique but found it produced 
non-reproducible values for some of the polluted water samples. 
Furthermore, in order to get the precipitate (in our case BaCO3) 
into the lab, we had to filtrate in the field with N2 in order to avoid 
uptake of CO2 from air. On the long run, all this was a bit annoying.

So we changed the procedure to releasing the DIC by addition of 
H3PO4. This method allowed us to take home a water sample of about 50 
ml, preserved with HgCl2 to avoid bacterial alteration, and it 
produced results with an excellent precision.


Frank Pawellek
Stable Isotope Laboratory
Department of Geography
University of Wales, Swansea
Singleton Park
Swansea SA2 8PP
Wales / GB

Tel. +44 1792 295149
Fax. +44 1792 205556