Am 21.07.2010 um 06:34 schrieb A. Schauer:
> Hi all,
> 1) How do you obtain a controlled 25*C for phosphoric acid digestion of carbonate in your lab? My lab varies around 22*C. It seems as though most water baths with heating option only control from 5*C above ambient to 99*C. Do you use a chiller model then or are you lucky enough to have a lab that is 20*C? Please either outline your method if home-built or provide a part number and manufacturer for your bath.
> 2) How do I know that my 25*C will be the same as your 25*C?
to (2) As long as you run calibrated standards (CO-1, NBS 19 or calibrated lab standards) together with your at identical conditions and normalize your data to the defined value (e.g. d13C for NBS 19 = +1,95 permil) absolute temperature does not matter at all. The standards in our lab will be same as in your lab, so temperature can be ignored. You can run your carbonates at any temperature you want as long as your temperature is _constant_ (in case of 18O analysis) for your standards and your samples.
to (1) since we run a gasbench with temperature stabilzed tray we never built our own system. But 18O water analysis (also temperature sensitive) I was happy by using a standard drying oven. We placed a styrofoam box with a tube rack in the drying cabinet and set the temperature controller to 26°C. However, since the acid reaction is a one way lane (instead of water equilibration) you have to be fast by injecting you acid. Otherwise your vials will cool down after taking it out of the oven... :-)