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<div class="moz-cite-prefix">Richard,<br>
<br>
in principle, a differential viscometer can yield not only
relative, but also absolute dynamic viscosities. Both p_i, the
inlet pressure, and delta p, the pressure difference between the
solution and the solvent branch, are absolute values - the
question is, does the instrument software give you access to these
raw data. The maths I used, however, only worked out for symmetric
branches, and the instrument we used at that time, a WGE eta-1002,
had assymmetrical branches. I never got to the point of solving
the more complicated case. Eventually, the viscometer broke down,
and I abandoned the project.<br>
<br>
However, a differential viscometer intended for use as an SEC
detector is very sensitive, and our measurements gave good data
also for diluted solutions. Consider that we had a constant eluent
flow and injected as little as 100 µl into that flow. So the
signal was actually for a solution yet more diluted than the bulk
solution. The intriguing point about this project was that if you
couple a second detector into the flow, like a UV, for
concentration of the solute, you get two sets of data: absolute
viscosities and absolute concentrations for every data point of
the elugram. This is equivalent to a number of independent
measurements at varied concentration. Thus, it should in principle
be possible to calculate even an intrinsic viscosity from a single
shot.<br>
<br>
The drawback is that the eluent flow is split into the two
branches, where a reservoir on the solvent branch, filled with
solvent at the beginning of the experiment, gradually fills with
solution containing the solute. You have only a couple of shots
until the solvent branch is contaminated with solute, and the
system needs to be purged. <br>
<br>
Though I never brought this to an end, it still appears a
promising option that should work out - in principle.<br>
<br>
Kind regards,<br>
Kristian<br>
<br>
Am 07.06.2013 05:53, schrieb Richard Kingston:<br>
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Thanks for the many informative replies, both on- and off- list.
<div><br>
</div>
<div>The consensus seems to be that differential
(pressure-imbalance) viscometers like the Viscostar are well
suited to the measurement of protein intrinsic viscosities, and
there are several in commercial production. However these
instruments, by design, measure only relative viscosities </div>
<div><br>
</div>
<div>Reframing my original question, I was really wondering if it
were possible to find an instrument which could measure absolute
solution viscosities with sufficient accuracy to allow protein
characterisation (and could therefore do double duty, being able
to measure solution viscosity for other biophysical
applications). However for the reasons outlined by Arthur, and
as attested below by Dave, it might be difficult to achieve good
results this way.</div>
<div><br>
</div>
<div>Best,</div>
<div><br>
</div>
<div>Richard</div>
<br>
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<br>
<pre class="moz-signature" cols="72">--
Nanolytics
Gesellschaft fuer Kolloidanalytik mbH
Dr. Kristian Schilling
Am Muehlenberg 11
D-14476 Potsdam
Tel: +49 331 5818360
Fax: +49 331 5818361
e-mail: <a class="moz-txt-link-abbreviated" href="mailto:schilling@nanolytics.de">schilling@nanolytics.de</a>
Internet: <a class="moz-txt-link-abbreviated" href="http://www.nanolytics.de">www.nanolytics.de</a>
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