[RASMB] sedimentation

[Kristian Schilling]

Arthur,

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.

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.

Cheers,
Kristian

At 12:47 24.10.2003 +0100, you wrote:
>Hi Irene
>
>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.
>
>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 is any real upper limit to the 
>size of spheres you can cope with, when running the AUC at low speeds.
>
>All best wishes for your work
>
>Regards
>
>Arthur
>--
>*******************************************************
>Arthur J Rowe
>Professor of Biomolecular Technology
>NCMH Business Centre
>University of Nottingham
>School of Biosciences
>Sutton Bonington
>Leicestershire LE12 5RD   UK
>
>Tel:        +44 (0)115 951 6156
>             +44 (0)116 271 4502
>Fax:        +44 (0)115 951 6157
>email:      arthur.rowe at nottingham.ac.uk
>             arthur.rowe at connectfree.co.uk (home)
>Web:        www.nottingham.ac.uk/ncmh/business
>*******************************************************
>
>From: "Irene Hallyburton" <i.hallyburton at dundee.ac.uk>
>Organization: Dundee University
>Date: Fri, 24 Oct 2003 12:09:48 GMT
>To: rasmb at rasmb-email.bbri.org
>Subject: Re: [RASMB] sedimentation
>
>---------------------------------------------------------------------------------- 
>
>The older archived RASMB emails can be found at:
>http://rasmb-email.bbri.org/rasmb_archives
>and current archives at
>http://rasmb-email.bbri.org/pipermail/rasmb/
>Search All the Archives at:
>http://rasmb-email.bbri.org/rasmb_search.html
>----------------------------------------------------------------------------------
>
>Hi All
>
>In the same vein as Jan's silica particles, a client has been using latex
>microparticles in the development of Point of Care assays. He has
>asked me about looking at them, coated and uncoated, in the AUC.
>They will be quite large, and we did consider DLS, but our instruments
>max is 50nm and they'll be bigger than that.
>
>What is the upper size range for AUC?
>
>Many Thanks
>
>Irene
>
>
>
>
>
><0>-<0>-<0>-<0>-<0>-<0>-<0>-<0>-<0>-<0>-<0>
>Irene Hallyburton
>Post Genomics & Molecular Interactions Centre
>Faculty of Life Sciences
>University of Dundee
>01382 348700
>
>
>
>_______________________________________________
>RASMB mailing list
>RASMB at rasmb-email.bbri.org
>http://rasmb-email.bbri.org/mailman/listinfo/rasmb



=================================
Nanolytics
Gesellschaft fuer Kolloidanalytik mbH
Dr. Kristian Schilling

Hauptstr. 20
D-14624 Dallgow

Tel.:           +49 3322 24200-5
Fax:            +49 3322 24200-6
e-mail: schilling at nanolytics.de
Internet:       www.nanolytics.de
   
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://list.rasmb.org/pipermail/rasmb-rasmb.org/attachments/20031024/3cf083bd/attachment.htm>