So, what do you propose people should do who happen to work with carbonates that are resilient to acid digest at 25 C but require higher temperatures to react, or, even "better", who are working with mixed carbonates where one (mineral) fraction reacts at 25 C but the other only just, and where 18O fractionation slopes will differ?
I call this the normative forces and facts of life; it's no good to moan this should be done strictly observing condition X because of Y if the reaction doesn't work at condition X in the first place. One has to be pragmatic and do they best one can under the circumstances.
As Willi pointed out already, to report 18O data to the standard temperature of 25 C independent of the actual temperature the digest had to be performed, 18O values must be back-calculated to 25 C.
What this boils down to is observance of the principle-of-identical treatment, i.e. concurrent digest and analysis of NBS19 and LSVEC plus one or two other standards as quality control (for the correction).
From: Stable Isotope Geochemistry on behalf of Pier de Groot
Sent: Sat 24/07/2010 17:23
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] 25*C and SI in concrete
Hi Robert and others,
First my two cents for references on concrete/mortar and isotopes:
Zouridakis, N. M., I. G. Economou, et al. (2000). "Investigation of the
physicochemical characteristics of ancient mortars by static and dynamic
studies." Cement Concrete Res. 30(7): 1151-1155 doi:
Rafai, N., R. Letolle, et al. (1992). "Carbonation-decarbonation of
concretes studied by the way of carbon and oxygen stable isotopes." Cement
Concrete Res. 22(5): 882-890 doi: 10.1016/0008-8846(92)90112-9.
Létolle, R., P. Gégout, et al. (1992). "Stable isotopes of carbon and oxygen
for the study of carbonation/decarbonation processes in concretes." Cement
Concrete Res. 22(2-3): 235-240 doi: 10.1016/0008-8846(92)90061-Y.
Häussler, F., F. Eichhorn, et al. (1990). "Monitoring of the hydration
process of hardening cement pastes by small-angle neutron scattering."
Cement Concrete Res. 20(4): 644-654 doi: 10.1016/0008-8846(90)90107-9.
And maybe still of use:
Graham, I. J., R. L. Goguel, et al. (2000). "Use of strontium isotopes to
determine the origin of cement in concretes: Case examples from New
Zealand." Cement Concrete Res. 30(7): 1105-1111 doi:
Than about the carbonate-isotope analytical procedure:
Your statement that temperature can be ignored in acid digestion of
carbonates for isotopic determinations did alarm me quite a lot, at least if
considering oxygen isotope determinations...
The oxygen isotopic fractionation of phosphoric acid digestion of the
carbonates is temperature dependent* in a non-linear way to my knowledge. If
this fractionation is not linear temperature is highly important, since if
we calibrate our system at 25°C or 22°C (or other T's) by acid digestion
different fractionation factors have to be used to estimate the value to
correct/calibrate to the proper scale.
Maybe you meant this yourself, but if so, I did not get the right picture
the way you described things - certainly not by the statmeent on
temperatures in your posting to the list.
* Let me quote from Rosenbaum and Sheppard (GCA, 1986, 50: 1147-1150):
"Since reaction with phosphoric acid liberates only two thirds of the oxygen
of the carbonate as CO2 gas, a temperature dependent fractionation of oxygen
Delta Isotopes Consultancy
Dr. Pier A. de Groot
De Schans 47
3945 Ham (Oostham)
Tel. +32 (0)11 72 77 66
e-mail: [log in to unmask]
Chair of the Programme Group ³Isotopes in Geosciences² [IG] and Secretary
for IG in the ³Geochemistry, Mineralogy, Petrology, Volcanology² [GMPV]
division of the European Geoscience Union (EGU)
EGU Home web-site: http://www.egu.eu/
Scientific Committee member of BASIS (Benelux Association of Stable Isotope
Visit the Elsevier WEB-site about my ³Handbook of Stable Isotope Analytical
Techniques² Vol-II (published Nov. 17, 2008):
and Vol-I (was published Dec. 27, 2004) at:
> From: Robert van Geldern <[log in to unmask]>
> Reply-To: Stable Isotope Geochemistry <[log in to unmask]>
> Date: Wed, 21 Jul 2010 09:11:14 +0200
> To: <[log in to unmask]>
> Subject: Re: [ISOGEOCHEM] 25*C
> Am 21.07.2010 um 06:34 schrieb A. Schauer:
>> Hi all,
>> 1) How do you obtain a controlled 25*C for phosphoric acid digestion of
>> carbonate in your lab? My lab varies around 22*C. It seems as though most
>> water baths with heating option only control from 5*C above ambient to 99*C.
>> Do you use a chiller model then or are you lucky enough to have a lab that is
>> 20*C? Please either outline your method if home-built or provide a part
>> number and manufacturer for your bath.
>> 2) How do I know that my 25*C will be the same as your 25*C?
> to (2) As long as you run calibrated standards (CO-1, NBS 19 or calibrated lab
> standards) together with your at identical conditions and normalize your data
> to the defined value (e.g. d13C for NBS 19 = +1,95 permil) absolute
> temperature does not matter at all. The standards in our lab will be same as
> in your lab, so temperature can be ignored. You can run your carbonates at any
> temperature you want as long as your temperature is _constant_ (in case of
> 18O analysis) for your standards and your samples.
> to (1) since we run a gasbench with temperature stabilzed tray we never built
> our own system. But 18O water analysis (also temperature sensitive) I was
> happy by using a standard drying oven. We placed a styrofoam box with a tube
> rack in the drying cabinet and set the temperature controller to 26°C.
> However, since the acid reaction is a one way lane (instead of water
> equilibration) you have to be fast by injecting you acid. Otherwise your vials
> will cool down after taking it out of the oven... :-)
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