Dear Mike and Million,

Mike might be referring to one of my papers on emu eggshell. There are a
couple of tricks. We used only 5 mg not 20mg. It should be enough with a
regular thickness eggshell. More is NOT necessarily better. We add the add
(6N) in 20 microliter aliquots. It does in fact seem as though some of the
acid "climbs" up and out of the boat. On the whole, yields are pretty
consistent.

When the samples have been acidified and left in a fume hood over night,
wipe the bottoms of the boats on a clean Kimwipe to get off the excess
acid. We use 96 well plates, and do about 24-36 samples at a time. More is
not a good idea.

After wiping off excess acid, place the boat into a clean well. Myself, I
like to do this one more time. After a day in the fume hood, dry the
samples until no salty brine comes off. Before turning into balls, put the
96 well plate with the samples into a hotter oven (80 C) until boats are
crisp. Roll and analyze immediately. If you need to hold them for awhile,
store them at 50 C.

Fuming doesn't work well with pure carbonate. What happens there is that
you form a crust of CaCl2, with a "pie" of unreacted carbonate. Fuming
works best with samples that have some carbonate in them, but are not
carbonate matrix-based.

When analyzing on the EA, make sure you have a plug of silver wool at the
bottom of the combustion reactor (about 10-15 mm). Also, it is imperative
that you change the water trap before you analyze these samples. My
feeling is that some acid is transferred to the trap and causes further
problems. Run the samples undiluted for Carbon.

We run them in batches of 24-36. Then let the EA columns "rest". Run
something else like plants or muscle tissue. Test again with standards,
and continue with another small batch. It is a bit tedious, but the old
method was much more difficult (see Bev Johnson's dissertation papers).
She was a whiz, but it was a week of full time intensive work to do 12
samples.

With the EA boat method, you can do about 75 in a week if you are patient
and pay attention to details.

Marilyn Fogel

> Mike,
>
>   You can use the fumigation method with 12N HCl. We did this for soils
to
> get ride of carbonate. You can fumigate it in a desiccator for 8 hours
in silver capsule, dry it then wrap it with tin capsules. There is a
published paper by David Harris how to fumigate you samples and for how
long. We got a very consistent result when we fumigate it for 8 hours.
>
>   Million
>
>
> Mike Polito <[log in to unmask]> wrote:
>   Hi all,
>
> I am working on penguin eggshells and am interested in methods of
carbonate removal for organic 13C and 15N analysis using an EA. I have
found
> conflicting results in the literature for the best way to do this
without
> losing
> any organic carbon or affecting 15N values.
>
> My current working methods are:
>
> Dissolving about 15 mg of cleaned eggshell in a silver capsule (9 mm x 5
mm)
> by titration with 6 N HCL. Evaporated at room temperature under a fume hood
> for at least 24 hours, then for at least 24 hours in an oven at 50 °C.
>
> Problems I have found with this methods include bubble over or leakage,
when
> adding the HCl (even adding very small amounts at a time), and lack of
complete drying.
>
> Any suggestions?
>
> Thanks for your time and help.
>
> Cheers,
>
> Mike
>
> Michael J. Polito
> University of North Carolina at Wilmington
> Department of Biology and Marine Biology
> 601 S. College Rd.
> Wilmington, NC 28403
>
>
>
> ---------------------------------
> Sucker-punch spam with award-winning protection.
>  Try the free Yahoo! Mail Beta.






Dr. Marilyn L. Fogel
Geophysical Laboratory
Carnegie Institution of Washington
5251 Broad Branch Rd., NW
Washington, DC 20015 USA
Phone: 202-478-8981
FAX: 202-478-8901
Website: http://fogel.ciw.edu