We have run enriched 15N (up to 10 atom % 15N) by EA. We have run
experiments to show that running a tray full of standards (even empty
tins) is sufficient to clean up the machine so that standards run at
their normal value. Running an empty tray (no tins) is not sufficient.
After running enriched samples, we change the insert (ash collector).
To be extra safe, we try to save 15N samples and run them just before
changing the reactors, but I believe this is actually unnecessary if
you run a tray of standards or empty tins.
As Gerry said, the biggest risk is contamination outside the EA.
We weigh enriched 15N samples in another lab, on another microbalance
which is not used for natural abundance N isotopes. Even then, we take
extra care to line the balance and work area and thoroughly wipe
everything down afterwards.
Science Foundation of Arizona Graduate Fellow
School of Earth & Space Exploration
Arizona State University
Tempe, AZ 85287
On Fri, Nov 13, 2009 at 10:23 AM, Linda Godfrey
<[log in to unmask]> wrote:
> Does any one have experience of successfully switching between
> isotopically enriched samples and natural abundance samples on a CF-IRMS.
> I think by double wrapping samples any possible surface contamination by
> the tin cups to the autosampler carousel/piston can be taken care of.
> There ought not be condensation of gases in the EA or capillary to the MS
> - is this correct or is it simply better to stay safe and not run enriched