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<TITLE>Re: Antwort: Re: [RASMB] sedimentation</TITLE>
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<FONT COLOR="#800000">Hi Lars, Kristian and everyone<BR>
<BR>
Yes, agreed. I put it a bit incautiously when I talked about 'no upper limit' to the size of particle one could study in the AUC. Certainly, once one gets into the range where the things are starting to drop out under 1 x g, you have gone too far.<BR>
<BR>
I am not sure, however, that the optical problems need be insuperable (Kristian). With a short optical path length centrepiece and a wavelength heading up towards the red end, you can get away with a fairly turbid solution. Higher solute concentrations may however give rise to refraction at a level where the refracted light from a boundary cannot be contained within the (modest) physical aperture of slit/lens assembly. And if you do get these 'schlieren' effects, then with big particles they are not going to vanish with time as a result of diffusion. As ever, "if it works, it works: if it doesn't - it doesn't".<BR>
<BR>
Arthur<BR>
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<BLOCKQUOTE><B>From: </B>lars.boerger@basf-ag.de<BR>
<B>Date: </B>Fri, 24 Oct 2003 14:10:29 +0200<BR>
<B>To: </B>"Irene Hallyburton" <i.hallyburton@dundee.ac.uk>, <rasmb@rasmb-email.bbri.org><BR>
<B>Subject: </B>Antwort: Re: [RASMB] sedimentation<BR>
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Hi Irene,<BR>
<BR>
the upper limit of particle diameters that can be addressed by AUC depends<BR>
- of course -<BR>
very much on the density your particles exhibit, the density and viscosity<BR>
of the solvent etc.<BR>
But from our experience as a rule of thumb 5 µm is a reasonable number for<BR>
latex particles<BR>
(With increasing diameter of the particles to be investigated slower speeds<BR>
have to be chosen,<BR>
but therefore - of course - the 1g earth's gravitational force acting<BR>
perpendicular to the gravitational<BR>
field caused by rotor spinning has to be taken into account more and more.<BR>
This is in practice the<BR>
reason for the existence of an upper limit in particle size analysis as<BR>
long as the Beckman type<BR>
of ultracentrifuge geometry is applied).<BR>
<BR>
Regards<BR>
Lars<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
"Irene Hallyburton" <BR>
<i.hallyburton@dundee An: rasmb@rasmb-email.bbri.org <BR>
.ac.uk> Kopie: (Blindkopie: Lars Boerger/ZK/BASF-AG/BASF) <BR>
Gesendet von: Thema: Re: [RASMB] sedimentation <BR>
rasmb-admin@rasmb-ema <BR>
il.bbri.org <BR>
<BR>
<BR>
24.10.2003 14:09 <BR>
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
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Hi All<BR>
<BR>
In the same vein as Jan's silica particles, a client has been using latex<BR>
microparticles in the development of Point of Care assays. He has<BR>
asked me about looking at them, coated and uncoated, in the AUC.<BR>
They will be quite large, and we did consider DLS, but our instruments<BR>
max is 50nm and they'll be bigger than that.<BR>
<BR>
What is the upper size range for AUC?<BR>
<BR>
Many Thanks<BR>
<BR>
Irene<BR>
<BR>
<BR>
<BR>
<0>-<0>-<0>-<0>-<0>-<0>-<0>-<0>-<0>-<0>-<0><BR>
Irene Hallyburton<BR>
Post Genomics & Molecular Interactions Centre<BR>
Faculty of Life Sciences<BR>
University of Dundee<BR>
01382 348700<BR>
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