[RASMB] Viscometer

[Kristian Schilling]

Richard,

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.

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.

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.

Though I never brought this to an end, it still appears a promising 
option that should work out - in principle.

Kind regards,
Kristian

Am 07.06.2013 05:53, schrieb Richard Kingston:
>
>
> Thanks for the many informative replies, both on- and off- list.
>
> 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
>
> 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.
>
> Best,
>
> Richard
>

-- 
Nanolytics
Gesellschaft fuer Kolloidanalytik mbH
Dr. Kristian Schilling

Am Muehlenberg 11
D-14476 Potsdam
Tel: +49 331 5818360
Fax: +49 331 5818361
e-mail:	schilling at nanolytics.de
Internet:  www.nanolytics.de
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