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<DIV>Here is the lamp intensity check procedure from a 10-2001 manual. I'd
follow this to step 8 then just look at it. The origin part is a waste of time
in my opinion.</DIV>
<DIV>John Gunhter</DIV>
<DIV><BR><FONT face=Arial size=2>*********** REPLY SEPARATOR
***********<BR><BR>On 4/4/2008 at 10:57 AM John Correia wrote:</FONT></DIV>
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style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid">
<DIV><FONT face=Arial size=3>It is worth noting that Beckman has a service
manual for the XLA XLI that discusses all of these features and tests and
specs. The spec for linearity is 20% when measured at 280 nm on a
windowless cell (or an empty hole) at 3000 rpm using OD values 1 cm
apart. The old manual specified 6.0 and 7.0 cm. With the old lamp
rotation of the lamp strongly influenced the intensity across the cell; the
newer lamp holder is now symmetric and do not vary as much with rotation,
in my experience. The old part # for this manual is 679045 but my copy
is dated 1/92. The newest version I am aware of is called Proteome Lab
XLA & XLI Service Manual dated (10/3). Sorry I do not have a part #
- the relevant chapter is section 3. It describes wavelength calibration
and accuracy checks, Intensity checks, cleaning the optics, radial position
calibration, etc, etc. Obviously depends upon the software you have as
well. In my opinion it is well worth buying or getting a copy for
your service guy - in the long run it saves both of you time. Why this
isn't standard operation procedure with Beckman is a very good
question.</FONT></DIV>
<DIV><FONT face=Arial size=3></FONT> </DIV>
<DIV><FONT face=Arial size=3> </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>-------------------------------------------------------------------<BR>Dr.
John J. "Jack" Correia<BR>Department of Biochemistry<BR>University of
Mississippi Medical Center<BR>2500 North State Street<BR>Jackson, MS
39216<BR>(601)
984-1522
<BR>fax (601)
984-1501
<BR>email address: jcorreia@biochem.umsmed.edu
<BR>homepage location: <A
href="http://biochemistry.umc.edu/correia.html">http://biochemistry.umc.edu/correia.html</A><BR>dept
homepage location: <A
href="http://biochemistry.umc.edu/">http://biochemistry.umc.edu/</A><BR>-------------------------------------------------------------------<BR><BR><BR><BR></FONT><BR>>>>
On 4/4/2008 at 10:18 AM, in message
<C7B1B01A69FC4164B0213B9168C3CBAA@79B7XD1>, "John Philo"
<jphilo@mailway.com> wrote:<BR></DIV>
<DIV
style="PADDING-LEFT: 7px; MARGIN: 0px 0px 0px 15px; BORDER-LEFT: #050505 1px solid; BACKGROUND-COLOR: #f3f3f3">Mitra,<BR><BR>To
my knowledge there is no specification for intensity variation across
the<BR>cell, but in my experience few instruments would vary as little as
10%.<BR>Probably 20-30% is more typical. It is a common mistake to think that
the<BR>absolute intensities have a strong effect on the signal/noise. It
is<BR>doubtful that you would notice the effect of even a 50% drop in
intensity<BR>(assuming you are starting from a normal level). Further,
positioning the<BR>lamp to give the maximum possible intensity will not
necessarily give the<BR>best overall performance---quite often the maximum
intensity position also<BR>gives high stray light and compromises the
linearity. <BR><BR>John<BR><BR>-----Original Message-----<BR>From:
mitrana@mail.utexas.edu [mailto:mitrana@mail.utexas.edu] <BR>Sent: Thursday,
April 03, 2008 6:00 PM<BR>To: jphilo@mailway.com<BR>Cc: 'RASMB'<BR>Subject:
RE: [RASMB] Lamp Diagnostics<BR><BR>John<BR>I feel better already.<BR><BR>What
I meant in 1. is that I take a wavelength scan at 5.9, 6.5, and 7.1 cm<BR>and
compare the 230 nm peaks. I guess a radial scan is definitely a better<BR>way
to check intensity variability across a cell. How much variability
is<BR>considered acceptable - somehow 10% seems stuck in my
head.<BR><BR>Mitra<BR><BR>Quoting John Philo
<jphilo@mailway.com>:<BR><BR>> Mitra,<BR>><BR>> Points 2 and 3
are normal. Every time the monochromator moves there is <BR>> an
uncertainty of +/- 1-2 nm (I believe the official specification is <BR>>
actually<BR>> +/- 4 nm).<BR>><BR>> Also for wavelength scans the
monochromator doesn't actually take data <BR>> at the exact wavelength
interval you ask for. So sometimes it will <BR>> essentially step over the
sharp peaks (if you double-click on the line <BR>> graph and ask it to mark
the data points with symbols you can more <BR>> easily see there are no
points where the peak should be).<BR>><BR>> I'm not sure I understand
your point 1, but I think the intensity <BR>> variability may just be a
consequence of the wavelength variability <BR>> discussed above. Normally
one would try to adjust the lamp alignment <BR>> using radial scans, not
wavelength scans, and typically the wavelength <BR>> intensity scans to
check the strength of the 230 nm peak or wavelength <BR>> calibration are
run at 6.5 cm.<BR>><BR>> John<BR>><BR>> -----Original
Message-----<BR>> From: rasmb-bounces@rasmb.bbri.org <BR>>
[mailto:rasmb-bounces@rasmb.bbri.org] On Behalf Of <BR>>
mitrana@mail.utexas.edu<BR>> Sent: Thursday, April 03, 2008 2:58 PM<BR>>
To: 'RASMB'<BR>> Subject: [RASMB] Lamp Diagnostics<BR>><BR>> Hello
Spinners<BR>> Our AUC started giving some problems recently. Did a
wavelength scan <BR>> and here's a summary of the results -<BR>><BR>>
1. Lamp intensity varies at the 5.9 cm position although at the
'sweet<BR>spot'<BR>> obtained from the lamp alignment this variation is
about 9-10%.<BR>><BR>> 2. Sometimes it seems the peaks are cut-off and I
get a plateau <BR>> instead of a peak with of course a lower intensity
count.<BR>><BR>> 3. The peak oscillates 1-2 nm (227-230 nm and 526-528
nm) on <BR>> successive scans at a single radial position.<BR>><BR>>
It seems like a monochromator problem to me but I'd like to hear some <BR>>
comments from experts here. I am particularly worried about the peaks <BR>>
getting cut-off.<BR>> Our facility did not renew the service contract this
year (I know, <BR>> extremely bad idea but too many size exclusion column
huggers around) <BR>> and I'd rather know the problem instead of being told
by the Beckman <BR>> Service person that it's within specs while charging
$290.00 per hour.<BR>><BR>> Mitra<BR>><BR>> --<BR>> Mitra S.
Rana<BR>> Graduate Student<BR>> Institute for Cellular and Molecular
Biology 2500 Speedway, UT-Austin <BR>> Austin, TX-78712
_______________________________________________<BR>> RASMB mailing
list<BR>> RASMB@rasmb.bbri.org<BR>> <A
href="http://rasmb.bbri.org/mailman/listinfo/rasmb">http://rasmb.bbri.org/mailman/listinfo/rasmb</A><BR>><BR><BR><BR>--<BR>Mitra
S. Rana<BR>Graduate Student<BR>Institute for Cellular and Molecular Biology
2500 Speedway, UT-Austin<BR>Austin,
TX-78712<BR><BR>_______________________________________________<BR>RASMB
mailing list<BR>RASMB@rasmb.bbri.org<BR><A
href="http://rasmb.bbri.org/mailman/listinfo/rasmb">http://rasmb.bbri.org/mailman/listinfo/rasmb</A><BR><BR></DIV><BR
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