Hi David,

Recently, I worked on both chloride- and sulfate-rich carbonate
samples (mainly calcite) in a 186 m saline sediment core from Death
Valley, California. I didn't realize any potential problems for these
samples and simply used the traditional method of McCrea (1950).
Unfortunately, I got really bad results. The Del values varied up to
560%o for Del C-13 and 53%o for Del O-18. These unbelievable data are
probably due to the contamination by HCl and/or SO2 gas produced by
partial reaction of the chloride and/or sulfate minerals with the
"dry" 100% H3PO4. I started to do a series of laboratory tests using
both laboratory standard and field samples. Finaly, I found that the
85% ortho phosphoric acid (without adding any thing) with reaction
time of 5 minutes (rather than 1 hour) at room temperature can give me
very good results (standard deviation < +/_ 0.2%o for both C and O).

Wenbo Yang
Dept. of Geology & Geophysics
University of Calgary
Calgary, AB, T2N 1N4, Canada
E-mail: [log in to unmask]
Tel: 403 220 3026
Fax: 403 284 0074 


In <v02130500ade73759a713@[192.149.148.118]>, David M. Anderson wrote:
>Another phosphoric acid question- Please respond if you have an answer!
>We are running a machine to measure calcium carbonate by the pressure
>evolved-no mass spec! :-(
>(reacting samples under vaccum in a common acid bath at 80 deg C)
>
>Although using the dry acid has been suggested, is there a reason we can't
>just use off the shelf 85% ortho phosphoric acid, avoiding the hydrogen
>peroxide, chromium trioxide altogether?
>thanks,
>dave anderson
>
>______________________________________________________________________
>David M. Anderson (Phone: 303-497-6237, FAX: 497-6513)
>NOAA Paleoclimatology Program, 325 Broadway Code E/GC, Boulder, CO 80303-3328
>______________________________________________________________________
>
>