[RASMB] What is wrong with my XLA?

[John Philo]

Steve,

I for one don't find your graphs of the meniscus region very informative
since they are all plotted in the same color. The sequence is important---is
the meniscus drifting to higher values over time, or just randomly moving
back and forth? A slow upward drift of the meniscus position is often simply
the result of some slow leakage of vapor to the vacuum, i.e. the red plug
gasket is not making a good vacuum seal. 

If you are getting random radial shifting of the meniscus (and presumably
other regions as well) that might arise from a problem with the radial
position potentiometer or its readout circuitry.

A blip or feature occurring in all scans (all cells) at the same radius
could indeed indicate a problem with the slit assembly, or might also be due
to some contaminant on the face of the photomultiplier. If you know how to
safely remove the slit assembly (be sure not to expose the PMT to room light
while the high voltage is on!) then you should do so, clean the PMT face
with alcohol, and also look for dirt or burrs on the underside of the slit
assembly that could keep it from riding smoothly across the PMT. Otherwise
it's time for a call to Beckman.

John

-----Original Message-----
From: rasmb-bounces at rasmb.bbri.org [mailto:rasmb-bounces at rasmb.bbri.org] On
Behalf Of smcbryan
Sent: Friday, July 16, 2010 1:01 PM
To: rasmb at server1.bbri.org
Subject: [RASMB] What is wrong with my XLA?

Fellow centrifugationistas,
Attached find two .png files of 1) two sample meniscus regions from data
collected in the intensity mode at 280nm, and 2) the resulting data from one
of these samples after time independent noise subtraction. 
almost certainly there is a problem with my slit assembly, resulting in the
menisci which defy fitting. My question is, is the very anomalous data
(which does not fit via van Holde-Weischet analysis)a result of ONLY the
meniscus jumping about, or is there perhaps another cause superimposed on
the slit assembly? 
Finally, there is a noise signature at 6.35cm in all sectors of all cells
always with this machine. I have cleaned the glass filter in the bottom of
the rotor chamber that protects the lamp, and blown some compressed air
gently into the slit in the monochrometer assembly. Neither act has removed
the offending noise. Any further suggestions for removal are appreciated. 
cheers,
steve


--
Steven McBryant, PhD
Director
Protein Production and Characterization Facility Research Scientist/Scholar
Colorado State University
970-491-5586