Dear Angie,

that is clear: Exposing an aqueous solution to an HCl atmosphere mixes HCL
with water forming chlorides in your sediment suspension. If you do not
wash out very thoroughly even traces of HCl and / or chlorides than this
could explain your weight increase instead of a decrese.

By the way: I had much troubles too in removing carbonates quantitatively
from soil and sediment samples. The point is that there is no standard
receipe apart from measuring carbonate by a carbonate machine to remove
carbonate quantitatively. I would make some tests to go sure otherwise you
will probably be surprised about the isotope values. You can destroy
carbonates and in another samples organic carbon. Via mass balance, carbon
and isotope measurements you should be able to decide which method give the
"most probable" results.

Currently, we destroy carbonates by heating 1 g of sample with about 20 ml
of 1N HCl (higher concentrations would lead to a severe hydrolysis of
labile organic compounds) 2 days in a water bath at 60 degrees. The results
obtained by this procedure fits best to the mass balance calculations with
the d13C values.

Hope this helps

Bruno

*******************************************************
Dr. Bruno Glaser
Institute of Soil Science and Soil Geography
University of Bayreuth
D-95440 Bayreuth
Germany
Email:[log in to unmask]
Web:http://www.geo.uni-bayreuth.de/bodenkunde
****************************************************************

-----Ursprungliche Nachricht-----
Von:    Angie Arnold [SMTP:[log in to unmask]]
Gesendet am:    Mittwoch, 9. Januar 2002 18:38
An:     [log in to unmask]
Betreff:        [ISOGEOCHEM] Trouble with carbonate removal from estuarine
sediments

I am trying to remove carbonate from samples from sediment cores taken in
the Chesapeake Bay using the method of Yamamuro and Kayanne(1995).  I am
trying to determine both the inorganic and organic carbon fractions and the
carbon isotopic signature of the organic matter.  These samples are
expected
to be 95-100% organic carbon.  50 microliters of Milli-Q water are added to
each sample.  Samples are exposed to 12N HCl for 6 hours in a dessicator
and
then dried in an oven at 75 C overnight. The problem arrising is that the
dried weights of the samples are heavier by 2-5 mg after exposure to HCl
and
drying than before.  I do not believe there is a problem with the
microbalance.  Has anyone experienced this problem or have any suggestions?
 Thanks.