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Arthur,<br>
<br>
we have sometimes been confronted with very large (and inorganic! - yugh
- rho > 4 g/ml) particles and have tried all sorts of tricks, like
increasing density as you suggested, or measuring near freeze-point to
increase viscosity... We have also found that you can run the XLI at 1100
instead of 3000 rpm. But according to our experience, sedimentation is
not as much a problem as detection. You can forget absorbance optics with
large particles, and even interference will be difficult when most laser
light is scattered away instead of reaching the camera and creating nice
interference patterns... With particles > 300 nm, the dispersion
usually gets so turbid that laser light will not pass through. If you
dilute sufficiently, you have practically no mass concentration left to
make fringes.<br>
<br>
Irene, I think 300 nm is a pretty good value for an upper limit. Of
course, an AUC equipped with turbidity optics can handle particles up to
the µm range, but I think only roughly three of us (not me!) have that
advantage.<br>
<br>
Cheers,<br>
Kristian<br>
<br>
At 12:47 24.10.2003 +0100, you wrote:<br>
<blockquote type=cite cite>Hi Irene<br>
<br>
There is a long history of using the AUC to look at PSL particles,
starting (I think) with a lovely paper by Cheng & Schachman (1955) J
Polym Sci 16:19+ which established what is still the most precise
reference data for validating the application of Stokes Law to small
spheres, as well as characterising the s-c dependence of such
spheres.<br>
<br>
As the density of PSL is quite close to 1, you can get away with looking
much larger PSL particles in the AUC than you could with denser (e.g.
protein-based) material. As you have the freedom to adjust the density
difference and make it even smaller by adding (say) salt or deuterium
oxide to the solvent, I doubt that there <u>is</u> any real upper limit
to the size of spheres you can cope with, when running the AUC at low
speeds.<br>
<br>
All best wishes for your work<br>
<br>
Regards<br>
<br>
Arthur<br>
<dl>
</dl>--<br>
*******************************************************<br>
Arthur J Rowe<br>
Professor of Biomolecular Technology<br>
NCMH Business Centre<br>
University of Nottingham<br>
School of Biosciences<br>
Sutton Bonington<br>
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<br>
<dl>
<dd>From: </b>"Irene Hallyburton"
<i.hallyburton@dundee.ac.uk>
<dd>Organization: </b>Dundee University
<dd>Date: </b>Fri, 24 Oct 2003 12:09:48 GMT
<dd>To: </b>rasmb@rasmb-email.bbri.org
<dd>Subject: </b>Re: [RASMB] sedimentation<br>
<br>
</dl>
<dl><tt>
<dd>----------------------------------------------------------------------------------
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<br>
<dd>Hi All<br>
<br>
<dd>In the same vein as Jan's silica particles, a client has been using
latex
<dd>microparticles in the development of Point of Care assays. He has
<dd>asked me about looking at them, coated and uncoated, in the AUC.
<dd>They will be quite large, and we did consider DLS, but our
instruments
<dd>max is 50nm and they'll be bigger than that.<br>
<br>
<dd>What is the upper size range for AUC?<br>
<br>
<dd>Many Thanks<br>
<br>
<dd>Irene<br>
<br>
<br>
<br>
<br>
<br>
<dd><0>-<0>-<0>-<0>-<0>-<0>-<0>-<0>-<0>-<0>-<0>
<dd>Irene Hallyburton
<dd>Post Genomics & Molecular Interactions Centre
<dd>Faculty of Life Sciences
<dd>University of Dundee
<dd>01382 348700<br>
<br>
<br>
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<br>
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