[RASMB] intensity issues

[John Philo]

Bo,

First, what is the wavelength? If this is up in the visible that low mean
intensity might be perfectly normal.

Second, are you sure these folks aren't using the SedVel 60K centerpieces
that have the lamp timing issue? That might produce an oscillation as the
lamp timing varies slightly. The oscillation does suggest some sort of
timing issue, so you might ask them to check whether the delay calibration
is in a normal range (you can see it from Service...Absorbance...Cal
Parameters).

Third, regarding the low intensity, is it possible there is a problem with
the 400 nm cutoff filter? Even if the control lever is in the right
position, I believe the filters have been known to become detached.


John 

-----Original Message-----
From: rasmb-bounces at rasmb.bbri.org [mailto:rasmb-bounces at rasmb.bbri.org] On
Behalf Of Borries Demeler
Sent: Thursday, April 03, 2008 8:07 AM
To: RASMB
Subject: [RASMB] intensity issues

Dear Colleagues,

I have an issue with an XLI at FSU - it has a strange problem with
intensity. First, it is very low, and second, it has a regularly spaced
intensity oscillation. Please see the attached image. It was generated by
scanning a channel containing just water in intensity mode and averaging the
intensity in the flat region over all points. The plot shows the average
intensity of the scans over a number of scans. The entire run shows this
consistent intensity fluctuation, and it is apparent in all cells. The run
was done at 50,000 rpm. Does anyone have a good suggestion as to what flaw
in the XLI could potentially cause such a pattern? Is this a lamp firing
issue, or a voltage issue with the PM tube or flash lamp? The machine was
just newly installed and configured by Beckman service, and this is the
pattern it produces.

Thanks, -borries