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problem</title></head><body>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite>Dear RASMB Colleagues,</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite>I am encountering a phenomenon with our
XLA which hopefully one of you has seen already and can help me out
with practical advice.</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite>We started to see a change in wavelength
during velocity scanning despite setting the instrument to continuous
scanning of one single wavelength only. Admittedly, "starting to
see" means actually that we "started to look", so I
don't know exactly for how long we have had this problem. Please view
the attached scan records. Our service engineer remains undisturbed,
since he considers these changes "within specs", but
pressed harder for an explanation/solution he inquired internally and
came back with the following explanation:</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite>Since the delay calibration was not
switched off the instrument performs it prior to each scan
thereby routinely moving the monochrometer to 500nm. Switching back
and forth between 500nm and our scan wavelength of 220nm is then
causing the variation. He suggested to speed up the rotor to the
desired speed and run the delay calibration once, switch it then off
(check NO DELAY CALIBRATION under options) and then "start the
run" Obviously, this approach needed to be altered to 1) fill
rotor with mock filled cell and counterbalance 2) spin it up to run
speed and acquire one scan with delay calibration 3) stop XLA and
reload rotor with sample cells 4) program run conditions with delay
calibration switched off 5) start velocity run.</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite>Short of time I did it this way for my
most recent velocity run, and the problem nevertheless remained. I
take this as further evidence that there is a instrument problem -one
which my service engineer apparently has not yet seen or at least is
reluctant to acknowledge as a problem. Therefore, I am looking for
something to tip him off as to what he should be looking
for.</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite>I truly hope some of you have some
ideas/suggestions what to do about this.</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite>Kind regards,</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite>Kate</blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><br>
<blockquote type="cite" cite><br></blockquote>
<blockquote type="cite" cite><br>
Cell 1:<br>
00001.RA1:R 1 04.0 60000 0000541 1.6990E10 220 1<br>
00002.RA1:R 1 04.1 60000 0000796 2.7040E10 220 1<br>
00003.RA1:R 1 04.1 60000 0001059 3.7450E10 220 1<br>
00004.RA1:R 1 04.1 60000 0001319 4.7710E10 220 1</blockquote>
<blockquote type="cite" cite><font color="#FF0000">00005.RA1:R 1 04.1
60000 0001580 5.8060E10 221 1</font><br>
00006.RA1:R 1 04.1 60000 0001834 6.8080E10 220 1<br>
00007.RA1:R 1 04.1 60000 0002096 7.8380E10 220 1<br>
00008.RA1:R 1 04.1 60000 0002350 8.8450E10 220 1</blockquote>
<blockquote type="cite" cite><font color="#FF0000">00009.RA1:R 1 04.1
60000 0002611 9.8720E10 221 1</font><br>
00010.RA1:R 1 04.0 60000 0002875 1.0910E11 220 1</blockquote>
<blockquote type="cite" cite><font color="#FF0000">00011.RA1:R 1 04.1
60000 0003137 1.1950E11 219 1</font><br>
00012.RA1:R 1 04.0 60000 0003394 1.2960E11 220 1<br>
00013.RA1:R 1 04.0 60000 0003666 1.4040E11 220 1<br>
00014.RA1:R 1 04.0 60000 0003923 1.5050E11 220 1<br>
00015.RA1:R 1 04.0 60000 0004175 1.6040E11 220 1<br>
00016.RA1:R 1 04.0 60000 0004430 1.7050E11 220 1<br>
00017.RA1:R 1 04.0 60000 0004683 1.8050E11 220 1<br>
00018.RA1:R 1 04.0 60000 0004942 1.9070E11 220 1<br>
00019.RA1:R 1 04.0 60000 0005193 2.0060E11 220 1<br>
00020.RA1:R 1 04.0 60000 0005446 2.1060E11 220 1</blockquote>
<blockquote type="cite" cite><font color="#FF0000">00021.RA1:R 1 04.0
60000 0005707 2.2090E11 219 1</font><br>
00022.RA1:R 1 04.0 60000 0005966 2.3120E11 220 1<br>
00023.RA1:R 1 04.0 60000 0006236 2.4180E11 220 1</blockquote>
<blockquote type="cite" cite><font color="#FF0000">00024.RA1:R 1 04.0
60000 0006492 2.5190E11 221 1</font><br>
00025.RA1:R 1 04.0 60000 0006761 2.6250E11 220 1<br>
00026.RA1:R 1 04.0 60000 0007026 2.7300E11 220 1<br>
00027.RA1:R 1 04.0 60000 0007280 2.8300E11 220 1<br>
00028.RA1:R 1 04.0 60000 0007531 2.9290E11 220 1<br>
00029.RA1:R 1 04.0 60000 0007786 3.0300E11 220 1<br>
00030.RA1:R 1 04.0 60000 0008034 3.1280E11 220 1<br>
00031.RA1:R 1 04.0 60000 0008295 3.2310E11 220 1</blockquote>
<blockquote type="cite" cite>00032.RA1:R 1 04.0 60000 0008553
3.3330E11 220 1</blockquote>
</blockquote>
<div>-- <br>
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></span>************************<br>
Katharina Spiegel, Ph.D. <x-tab>
</x-tab><x-tab>
</x-tab>Research Assistant Professor<x-tab>
</x-tab><x-tab> </x-tab><br>
Off:<x-tab>
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</x-tab>Manager, Keck Biophysics Facility<br>
Lab:<x-tab> </x-tab>847-467-6534<x-tab>
</x-tab><x-tab>
</x-tab>Northwestern University, Dept. BMBCB<br>
Fax:<x-tab>
</x-tab>847-467-6489<x-tab>
</x-tab><x-tab>
</x-tab>2153 N. Sheridan Road<br>
Email: k-spiegel@northwestern.edu<x-tab> </x-tab>Evanston, IL
60208 USA<br>
<br>
http://www.biochem.northwestern.edu/Keck/<span
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