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Hi Wolfram,

You did understand wrongly I think. Of course we can react at other
temperatures, but than we require to know the isotopic fractionations of the
specific carbonate by the specific temperature (e.g. obtained by
experimental methods, there are some fractionations at different
temperatures reported in literature, one example already given in my former
posting: Rosenbaum and Sheppard, GCA, 1986, 50: 1147-1150; they did
experiments on higher reaction temperatures and reported the isotopic
fractionation factors of some 'resistive' carbonates, such as dolomite,
siderite and ankerite), and the temperature should be well controlled (the
lower the reaction temperature the more critical this is because of increase
in fractionation factor vs. decrease of T).

I prefer to use the proper isotopic fractionation factor instead of
calculation, more error is introduced by a calculation method, and still we
require to know the different isotopic fractionations: of the applied
digestion temperature and the 25°C digestion.
In case of proper isotopic fractionations are applied we do not require 'to
report to 25°C', since the proper isotopic value is produced if using the
proper isotopic fractionation factor - the temperature of digestion actually
is of no importance except for knowing the correct fractionation factor at
that specific T, all only true if we calibrate our system accordingly by
digestion of our standards at the same conditions as the samples.
The proper isotopic fractionation (at the applied T) is of importance!
We obtain the isotopic value directly calibrated to our standards (also
digested at the same temperature as the samples, of course, as stated above)
and we do not require any extra step of calculation which will introduce
more error.
What is mixed up here is that the calibration of the carbonate system was
defined by 25°C digestion (on calcite!), and still forms the basis of our
systematics. It does not imply we have to recalculate all our samples to a
25°C digestion situation, however. If using the correct fractionation
factor, at any temperature applied, and as long as the standards are
digested at the same conditions (means a proper calibration), we do a proper
job. 

Willi's remarks about mixtures of carbonates basically can be found
published during the 1960's and 1970's where several methods how to handle
acid digestion of mixtures of carbonates were described (see also my review
on acid digestion, including mixtures of carbonates, and also digesting
carbonates at temperatures other than 25°C in my handbook Vol. 2, chapter
4-5 and references therein). Actually there are other factors of importance
with the acid digestion than just the temperature, such as density of the
phosphoric acid (should be between 1.90 to 1.92, sometimes called '103%
acid') and grainsize of the sample to be digested, to name some.
For instance, if we have a mixture of calcite and dolomite, we can apply a
'time-separated' method. We load the mixture in a usually used container for
acid digestion of carbonates and start digestion (at 25°C). After a time
period of one to two hours we will have released as good as all CO2 from the
calcite, while the dolomite stil has not reacted (dolomite reacts very
slowly at 25°C and first after ~4 hours a measurable amount of CO2 can be
detected, after experiments as reported in literature). Extract the
calcite-CO2 for measurement on the IRMS and continue reaction for at least 4
days to obtain the dolomite-CO2. Alternatively we can raise the temperature
after extraction of the calcite-CO2 and accordingly can react for shorter
time for the dolomite (and have to include the changed fractionation factor
also, of course). This was the most used procedure to my knowledge - some
other methods were also described (see my review as mentioned above).

Indeed we have to use NBS19 and LSVEC, and if wished some other standards
for quality control although not strictly required, for calibration of our
system.
But the calibration has to be 'adjusted' for the deviating temperature
digestion, either by application of the NBS19-LSVEC standards themselves at
the used T of digestion or else use of laboratory standards, calibrated to
the NBS19-LSVEC, at the applied T of digestion. Calculation is possible, but
includes more work and may introduce more error - the isotopic fractionation
factors of the digestion at the applied and the 25°C T's have to be used
anyway for the calculation, this since the isotopic fractionation is not
linear.

Why the 'good old methods' are not followed and some deviative methods which
only introduced bias had to be imported, I do not know. Best is to look what
was done before and use the good of it and only change those matters that
really require improvement. We must not try to invent the wheel again,
certainly not if the new wheel is 'less round' than the old one!

So, my posting had nothing to do with 'moaning' or anything like that. It
just is on what I brought forward to be erroneous in what was described!
I agree we have to life with non-ideal conditions and do our best to make
the good of it. Pragmatism is good as long it uses the right paths'.. And
the 'the principle-of-identical treatment' is correct, as long as that
treatment is the right one.

I hope you can agree with the comments as given above, and I did not shock
you too much with the 'old' but, what I tried to explain, correct
procedures.

Have a nice Sunday Wolfram,
Pier.

****************************************************************
Delta Isotopes Consultancy

Dr. Pier A. de Groot
De Schans 47
3945 Ham (Oostham)
Belgium
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
Scientists).
http://www.basis-online.eu/

Visit the Elsevier WEB-site about my ³Handbook of Stable Isotope Analytical
Techniques² Vol-II (published Nov. 17, 2008):
http://www.elsevierdirect.com/product.jsp?isbn=9780444511157
and Vol-I (was published Dec. 27, 2004) at:
http://www.elsevierdirect.com/product.jsp?isbn=9780444511140

****************************************************************


> From: Wolfram Meier-Augenstein <[log in to unmask]>
> Reply-To: Stable Isotope Geochemistry <[log in to unmask]>
> Date: Sun, 25 Jul 2010 09:53:20 +0100
> To: <[log in to unmask]>
> Subject: Re: [ISOGEOCHEM] 25*C and SI in concrete
> 
> Hi Pier,
>  
>  
> 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).
>  
>  
> Best,
>  
> Wolfram
> 
>  
> ________________________________
> 
> 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:
> 10.1016/S0008-8846(00)00280-5.
> 
> 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:
> 10.1016/S0008-8846(00)00248-9.
> 
> 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
> isotopes occur."
> 
> Best regards,
> Pier.
> 
> ****************************************************************
> Delta Isotopes Consultancy
> 
> Dr. Pier A. de Groot
> De Schans 47
> 3945 Ham (Oostham)
> Belgium
> 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
> Scientists).
> http://www.basis-online.eu/
> 
> Visit the Elsevier WEB-site about my ³Handbook of Stable Isotope Analytical
> Techniques² Vol-II (published Nov. 17, 2008):
> http://www.elsevierdirect.com/product.jsp?isbn=9780444511157
> and Vol-I (was published Dec. 27, 2004) at:
> http://www.elsevierdirect.com/product.jsp?isbn=9780444511140
> 
> ****************************************************************
> 
> 
>> 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... :-)
>> 
>> 
>> regards,
>> Robert
> 
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