[RASMB] Radial-dependent noise in Beckmann XL-I

[Borries Demeler]

I think Andrew is right on target. My suggestion would be to run a cell 
filled with *water* in both channels and do 5-10 intensity scans, not absorbance
scans, and then to compare the intensities across the cell. This can be 
repeated at different wavelengths and temperatures to see if there is
really a temperature dependence to this.

If the pattern between 6.2-6.4 shows up in *both* channels, then the issue
is most likely a dirty optical component, probably in the slit assembly
and/or lamp window.  It could also be a problem with your monochromator,
but check the other components first,  the monochromator should only be
serviced by Beckman. You could even intensity-scan an empty rotor hole
and get the same diagnostic.

-borries

On Thu, Jan 26, 2012 at 02:30:55PM +0000, Leech, AP wrote:
> Hi All,
> 
> From Anna's mention of different wavelengths I would infer it is seen
> in absorption measurements rather than interference. However I agree
> that running experiments away from 20C does seem to result in oil
> deposition in odd places.
> 
> I would look at the intensity data from the scans for sample and
> reference to see if there is a "drop" in light intensity, it could
> be oil condensing somewhere along the light path anywhere from the
> lamp to the photomultiplier tube, but the lamp assembly, any windows
> and the monochromator are easiest to check.
> 
> Hope this helps,
> 
> Andrew
> 
> 
> On 26/01/2012 13:43, Antje Voelkel wrote:
> >Dear Anna,
> >
> >maybe you have a bit of oil dust condensed on the lens of the
> >interference optics in the chamber. You can clean it with ethanol and a
> >tissue. Eventually you have to repeat this two or three times. I check
> >if its clean with the interference optics at low speed through an empty
> >rotor hole. We sometimes have this problem if the measuring temperature
> >differs from the room temperature. Most of the time heating is worse.
> >
> >Hope this helps!
> >Best regards
> >Antje
> >
> >
> >
> >Am 26/01/2012 13:33, schrieb anna vitlin:
> >>Hello,
> >>We have a Beckmann XL-I running a An-60 Ti rotor.
> >>When running sedimentation velocity experiments at 4 deg. we have
> >>noticed protein-independent, time-independent, radial-dependent noise,
> >>consistently between 6.2 and 6.4 Radius.
> >>This phenomenon occurs using different cell assemblies, different
> >>wavelengths and different velocities but does not occur at 20 deg.
> >>Has anyone detected behavior like this and how do we troubleshoot it?
> >>Should we call for service?
> >>Thank you
> >>Anna Vitlin
> >>Tel-Aviv university
> >>
> >>
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> >
> >--
> >Antje Voelkel
> >Max Planck Institute of Colloids and Interfaces
> >Am Muehlenberg 1
> >D-14476 Potsdam
> >+49(0)331 567 9528/9531
> >
> >
> >
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> 
> -- 
> Dr Andrew Leech                   *  Laboratory Head
> Technology Facility               *  Molecular Interactions Laboratory
> Department of Biology (Area 15)   *  Tel   : +44 (0)1904 328723
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