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Geochemical Journal
Geochemical Journal An open access journal for geochemistry
Published for geochemistry community from Geochemical Society of Japan.

A simple method for sampling total dissolved carbonate in carbonate-rich natural waters and CO2 preparation for δ13C determination

Minoru Kusakabe
Geochemical Journal, Vol. 35, No. , P. 459-464, 2001


A field-oriented, simple technique to determine the stable carbon isotopic ratio of the total dissolved carbonate in carbonate-rich natural water is proposed. The total dissolved carbonate is fixed in situ in a plastic syringe containing saturated Ba(OH)2 solution. The BaCO3 precipitate is purified without contact with atmospheric CO2. The dried precipitate is reacted with concentrated phosphoric acid in a capped, 5 ml glass syringe at 50°C overnight. A majority of the resulting CO2 is expanded into a vacuum line and purified in a trap before mass spectrometric δ13C determination. The effect of coexisting SO42- ion on δ13C determination becomes appreciable when the carbonate mole fraction in the precipitate, i.e., BaCO3/(BaCO3 + BaSO4), becomes smaller than 0.3. This technique can be applied for natural waters containing total carbonate waters down to <2.5 mmole/kg with the precision better than ±0.03‰.

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