For aqueous solutions of carbonate (bicarbonate) using HCl to evolve CO2 would in principle be no problem since the oxygen signature of dissolved carbonate would already be equilibrated through O-exchange with water. In principle, because even the most concentrated bottled HCl is still a "solution" of HCl gas in water. In other words, even 6N HCl is not water free. That being said, how much O(H3+) from HCl would exchange with dissolved carbonate / bicarbonate would be a matter of mass balance. If only one drop of 16N HCl (fuming HCl) is required to release all carbonate as CO2, the effect on its 18O composition would be minimal. However, in this case one might as well introduce gaseous HCl into the DIC solution and be done with it.
Using 100% ortho-phosphoric acid (100% = water free) is the traditional method of choice to release CO2 from solid (mineral) carbonates. For easily digested solid carbonates even 100% water free H2SO4 would do.
Prof. Dr W Meier-Augenstein, CChem, FRSC
Stable Isotope Forensics & Analytical Sciences
Robert Gordon University
School of Pharmacy and Life Sciences
T.: +44 (0)7979 742853
E.: [log in to unmask]
From: Stable Isotope Geochemistry [[log in to unmask]] On Behalf Of Christian Dietz [[log in to unmask]]
Sent: 02 October 2014 08:50
To: [log in to unmask]
Subject: [ISOGEOCHEM] why not HCl
i was wondering why no one uses HCl for extraction of dissolved inorganic carbon from water for measuring d13C.
At first glance it should be more suitable than H3PO4 since you don't have to expect O exchange from acid to evolved CO2. But I guess there must be a reason....
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