Here's one more trick to keep the acid and other liquids from "climbing" out
of the boat.  I noticed the same thing while trying to analyze dissolved
organic carbon and nitrogen isotopes by evaporating into EA boats (before I
got my automated TOC-IRMS system).  It apears that the liquids "climb" the
capilaries formed by the folds of the boat.  Eliminate the capilaries and
you eliminate the climbing.  I did this by machining a plate with holes or
pockets that were 6 mm in diameter but only 5 mm deep.  Therefore a standard
5 x 9 mm boat sticks out half way.  Once the boat is in, one can then gently
unfold the top of the boat so that it is open like a flower.  The folds
can't be eliminated, but as long as the gap between each fold is visible (>1
mm or so), there will no longer be capilary action to draw the liquid out of
the boat.  It is common to miss one fold or two, but the amount leaving the
boat is much reduced by doing this.

The second trick is to add combusted diatomaceous earth (sediment below
diatom rich waters and therefore mostly diatom silicate frustrules, sold by
Costech as Chromasorb W) to the bottom of the boat.  It has such a strong
capilary effect that it holds much of the liquid from climbing the
capilaries of the boat folds.  For eggshells, you might put your eggshell in
first, then put a little diatomaceous earth on top of that.

_____________________________________________________________________
Anthony K. Aufdenkampe, Ph.D.
Assistant Research Scientist - Isotope & Organic Geochemistry Stroud Water
Research Center 970 Spencer Road Avondale, PA 19311
Tel:  610-268-2153 ext. 263
Fax   610-268-0490
http://www.stroudcenter.org/about/aufdenkampe.htm


-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf
Of Marilyn Fogel
Sent: Tuesday, March 27, 2007 9:17 PM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] Methods of carbonate removal for organic 13C and
15N Analysis of Eggshell

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
>
>
>
> ---------------------------------
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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