Dear Dachen:

 Your observation is quite correct. The continuous extraction of CO2 means
that there is no equilibrium. In a way you are extracting dissolved CO2,
which is heavier and it is mixing with the gaseous CO2. One can perform such
calculations using volume of water, CO2, and container, the equilibrium
constant for carbonic species like KH, K1, and K2, the coefficient of
fractionation for different carbonic species and amount of CO2 extracted
each time.

Best wishes

Mahendra





----- Original Message -----
From: "Dachun Zhang" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, October 21, 2004 1:51 PM
Subject: dissolved CO2


> Hi,
>
> How much differences are the d18O  of  head space CO2 and the CO2
dissolved
> in water (40 oC)? I found d18O is inreasingly heavier when the CO2 is
> continusly sampled out from the head space and measuered for isotopic
> composition.
>
> Regards.
>
> Dachun Zhang
> Zymax
>