There is always problem in the isotopic analysis of hyper-saline water. The
"Old" method of distillation before analyzing also has some limitations. It
is needed a complete distillation. The remaining salts have some trapped
water, which may contribute considerable analytical uncertainty.
The alternative procedure for O-18 analysis could be performed with
equilibrating for longer time (24 hrs with agitations).
Besides the quality of isotopic analysis, the quality of chemical analysis
produces significantly higher uncertainty in our geochemical modeling of
natural systems. I tried to illustrate it in a paper on the CO2-H2O isotopic
exchange equilibrium which will be published in the Proceedings of
"Symposium on Quality Assurance for Analytical Methods in Isotope
Hydrology", IAEA, Vienna.
Recently, I analyzed the quality and consistency in the thermodynamic data.
I found that the dissociation constant of water are inconsistent
thermodynamically (Verma, M.P. (2004) Internal consistent thermodynamic data
for the dissociation constant of water Kw. In: Wanty, R.B. and Seal II, R.R.
(eds.) Water Rock Interaction (2004), Volume 2, pages 1413-1418).
Now, what I found is also a surprise to me. The steam tables of pure water
are also inconsistent thermodynamically. Let me cite an example: according
the steam tables there is H=2000 kJ/kg for the T=700 K and P=63.458 MPa or
P=456.356 MPa). If we consider T and H as independent variables, it is
impossible to predict the right value of P. The meaning of two P values is
that this is not an exact solution. This way- thermodynamics is not an Exact
Science. Let us further exemplify the above situation. We have a container
filled with water at T=700 K and P=63.485. Since there is same H (2000
kJ/kg) for P= 63.458 and 456.356 MPa at T= 700 K, it means we can pressurize
(from 63.458 to 465.356 MPa) the container without any work. In other words,
we can increase the pressure in a system of constant V and T without doing
IT IS EQUIVALENCE TO SAY THAT A STATE FUNCTION CAN HAVE MULTIPLE VALUES AND
ENERGY CAN BE CREATED OR DISTROYED.
I found that it is impossible to measure the thermodynamic properties of a
liquid (water) as have been measured in the literature. I am submitting an
article on it in the coming Stanford Geothermal Workshop. If anyone
interested to read it, I can send a copy it.
In summary, the quality of isotopic analysis is not only a problem. There
are very severe problems in the chemical analysis and thermodynamic data,
which are the limitations to geochemical modeling of any natural system than
the quality of isotopic analysis.
----- Original Message -----
From: "Tiziano Boschetti" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, December 08, 2004 8:11 AM
Subject: Re: hypersaline samples
> Dear Raj,
> I think that the "old" off-line method (azeotropic distillation + CO2
> equilibration + IRMS analysis) is the best way of analyse hypersaline
> waters (brines).
> Tiziano Boschetti
> Dipartimento di Scienze della Terra - UniversitÓ di Parma
> (Earth Sciences Department - University of Parma)
> Parco Area delle Scienze 157a
> 43100 Parma, ITALY
> Fax: +39-(0)521-905305
> e-mail1: [log in to unmask]
> e-mail2: [log in to unmask]
> ----- Original Message -----
> From: "Selva Marimuthu" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Wednesday, December 08, 2004 1:19 PM
> Subject: [ISOGEOCHEM] hypersaline samples
> > Dear List members.
> > I have been sending hyper saline water samples for deuterium and
> > analysis. The lab uses pyrolisis method (Finnigan Delta Plus XL ion
> > mass spectrometer and Thermochemical Conversion Elemental Analyzer
> > peripheral to analysis these samples. I have been using these results
> > correcting for the salt effect.
> > Lately, I was told that measurements are usually difficult in
> > sample because of the saturation of salts is attained and therefore the
> > isotopic effects become more complex as the exchange rate between CO2
> > water slow down considerably.
> > I'm bit confused, can someone explain to me how the pyrolisis method
> > hypersaline samples.
> > Thanks in advance for any help.
> > Regards
> > Raj