An excellent, if not the definitive, source for information on measuring and
calculating species of the dissolved carbonate system can be downloaded from
http://andrew.ucsd.edu/co2qc/handbook.html.  This Handbook describes all the
practical and real world considerations that textbooks tend to leave out.
The bottom line is that doing these measurements well is not as easy or as
simple as textbooks might lead you to believe, especially in seawater where
relative differences from site to site are minimal.

The titration described by Ian below will give you total alkalinity.  A
good, practial document on how to do alkalinity titrations in freshwater can
be downloaded from:
http://water.usgs.gov/owq/FieldManual/Chapter6/section6.6/

My experience with quantitiative DIC measurements, although not on an IRMS,
is that gas-tight sample handling is the most important factor in getting
good data.  It is very impressive how easily it is to unintentially
equilibrate (at least partially) a DIC sample with the atmosphere.  My guess
is that once sample handling is done well, then the Gas Bench - DeltaPlus
set up would work very well for quantification.

Happy reading.
Anthony
_____________________________________________________________________
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 ian cartwright
Sent: Monday, April 23, 2007 3:14 AM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] DIC quantification by Delta XP

Matheus

We also tried it with little success. However, Dissolved HCO3, CO2, and CO3
concentrations are easy to measure by acid/base titration. Any of the
general geochemistry books (Drever, Stumm & Morgan, Langmuir etc) have the
methodology. We use a digital titrator and pre-packed reagents from by Hach
(worldwide suppliers of this type of kit) which is very easy to use and do
our DIC measurements in the field.

Ian

______________________________________________

Dr Ian Cartwright
Head - School of Geosciences
Hydrogeology and Stable Isotopes
Monash University
Clayton Vic. 3800, Australia
t: 03 9905-4887 / 4879, f: 03 9905-4903

...water, our greatest resource