There appears to be some difference of opinion in the stable isotope community
regarding the preferred method for removal of organic material from carbonates
(calcite in bulk sediment, ostracodes, forams, etc) prior to extraction/analysis
for O and C isotopes.  Soaking in bleach or hydrogen peroxide solutions are time
consuming and appear to introduce small shifts in the isotopic composition of
the carbonate.  Vacuum roasting, while more time efficient, also introduces
errors from what I have heard and read.  Plasma ashers appear efficient, but I
do not know what, if any, changes they effect.

I searched the ISOGEOCHEM archive and found that this issue was raised about a
year ago.  Only one response to the initial question was tendered.  At the risk
of being redundant I would like to open the topic for discussion again.

We have dealt with H2O2 and bleach solutions and are currently looking at
alternatives to these methods.  With this is mind, what are the
advantages/disadvantages of using a plasma asher versus vacuum roasting for the
removal of organic material?  Are there any references addressing the issue?



Reed McEwan
Stable Isotope Lab
Univeristy of Minnesota