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<TITLE>Re: WG: [RASMB] nanoparticles</TITLE>
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<BLOCKQUOTE>Greetings, everyone<BR>
<BR>
Those are excellent points which Wendel makes, and Helmut's chapter in the AUC Book is indeed a mountain of useful information. <BR>
<BR>
It is I agree much better, if you are characterising a broad distribution, to use interference optics. However, if the distribution is a 'narrow cut' one (and Louise's original query referred to 30 nm particles) then you can validly use absorption optics, even though no actual true 'chromophore' is present. However, it needs also to be noted that speed of data acquisition is of importance, especially when dealing with high s values, and the interference detector wins hands down on that one. Although, as I calculate, even the dear old slowly working Beckman scanning system is fast enough for 30 nm particles - although not for micron sized ones, for sure.<BR>
<BR>
As regards the issue of 'enormous dilutions', I think there is a cultural thing going on here. Protein chemists do much of the time work with their solutes in the range of 0.1 to 1.0 mg/mL. So going down a bit further for colloidal particles is no great thing. And <U>again for narrow cut distributions</U>, high dilution limits the danger of excessively steep gradients (about which, Svensson theory and all that, see my recent RASMB contribution) causing distortion or even loss of information.<BR>
<BR>
Regards to all<BR>
<BR>
Arthur<BR>
<BR>
<BR>
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<BLOCKQUOTE><TT>Dear Louise,<BR>
<BR>
yes, we have characterized lots of these and other nanoparticles with the<BR>
AUC. There is an excellent overview on this topic by Helmut Cölfen in the<BR>
2005 AUC-book.<BR>
<BR>
1) Since inorganic particles have rather high dn/dc, scattering starts at<BR>
small diameters. When measuring agglomerates, you may have to dilute<BR>
enormously to get light through to the interference detector. The<BR>
Interference detector is much more reliable. The absorption signal is not<BR>
proportional to mass fraction, but instead is weighted by turbidity. In<BR>
fact, time-scanning turbidity detectors at fixed radius are sometimes even<BR>
more preferrable: They capture the entire bunch of agglomerates up to µm,<BR>
and they see the primary particles down to ~15nm.<BR>
2) Because of polydispersity from association or agglomeration you may not<BR>
capture the entire distribution at a single speed. We measure in the same<BR>
cell successively at increasing speeds. You can log/log-plot the multiple<BR>
size distributions and thus construct the entire distribution.<BR>
3) Density is in general not known. Even inside the nanoparticle, many of<BR>
them do not reach bulk density, and additionally comes the effect of the<BR>
surface layers. We normally calculate with the bulk density anyway, knowing<BR>
from comparison with TEM that we tend to underestimate the diameter by some<BR>
10%.<BR>
4) I can only support Arthur that ls-g(s*) is the approriate fitting<BR>
algorithm. Diffusion is very weak, especially when you work with fast<BR>
speeds and the interference detector.<BR>
<BR>
<BR>
Beste Grüße, Wendel<BR>
<BR>
<BR>
Dr. Wendel Wohlleben<BR>
Polymer Physics<BR>
<BR>
<BR>
Phone: +49 621 60-95339, E-Mail: wendel.wohlleben@basf.com<BR>
Postal Address: BASF Aktiengesellschaft, GKP/O - G201, D-67056<BR>
Ludwigshafen, Germany<BR>
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BASF - The Chemical Company<BR>
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Louise Creagh <BR>
<alcreagh@chml.ub <BR>
c.ca> An<BR>
Gesendet von: rasmb@server1.bbri.org <BR>
rasmb-bounces@ser Kopie<BR>
ver1.bbri.org <BR>
Thema<BR>
[RASMB] nanoparticles <BR>
24.10.2006 21:31 <BR>
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Hello,<BR>
Does anyone have experience in running samples containing nanoparticles<BR>
(30 nm diameter; copper, iron, silver or gold) in aqueous buffer<BR>
solutions on the XL-I?<BR>
Thank you.<BR>
Louise Creagh.<BR>
University of British Columbia.<BR>
<BR>
--<BR>
Louise Creagh<BR>
<BR>
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