First I would like to thank all of you who replied on the storage of IAEA
standards.  The information was very useful.

We are using FM Gas Bench for 18O equilibrations with 0.2% CO2 in
Helium.  This method usually works very well.  Unfortunately we have a
batch of water extracted from grass leaves that report results that make no
sense.  It appears that some of them actually generated CO2, while other
took it out of the atmosphere!  Running them twice made no difference and
yet other samples and standards in the run analyzed very well.

It has been suggested that this is probably due to contamination from
organic volatiles in the sample, and that we should add some activated
charcoal to each sample, shake them and then re-equilibrate them.  I am not
familiar with this method.  Has anyone else ever used this and do they have
a reference and suggestions as to the type of carbon?

Thanks in advance,

Paul.





Paul D. Brooks,
Dept. ESPM-ES,
147 Higard Hall MC 3110,
UC Berkeley, Ca. 94720-3110.

phone (510)643-1748,
FAX (510)643-5098.