If you analyze only carbon isotope, even 24 hour reaction time would be OK at 70 C, only the oxygen isotope is altered.  Please read the paper:

Rvsz, K.M., and Landwehr, J.M., 2002, 13C and 18O isotopic composition of CaCO3 measured by continuous flow isotope ratio mass spectrometry: Statistical evaluation and verification by application to Devils Hole core DH-11 calcite: Rapid Communications in Mass Spectrometry, v. 16, p. 2,102-2,114.

Kinga Revesz
Research Chemist, Stable Isotope Laboratory
U.S.Geological Survey
MS 431
Reston, VA 20192
FAX: 703-648-5274


From: "[log in to unmask]" <[log in to unmask]>
To: [log in to unmask]
Date: 05/07/2011 07:59 PM
Subject: carbonate reaction temprature for GasBench
Sent by: Stable Isotope Geochemistry <[log in to unmask]>

Most labs react carbonates (calcite) with phosphoric acid at 25 C for 24 hours to run them on the GasBench.

If I remember correct while running Kiel Carbonate device the temperature for reaction was 70 C and the reaction time was around 40 (?) minutes. Is there any reason that will affect the isotope values if I react calcite for GasBench for an hour at 70 C and running them right away?