[RASMB] Lamp Diagnostics

[John Philo]

Mitra,

Points 2 and 3 are normal. Every time the monochromator moves there is an
uncertainty of +/- 1-2 nm (I believe the official specification is actually
+/- 4 nm). 

Also for wavelength scans the monochromator doesn't actually take data at
the exact wavelength interval you ask for. So sometimes it will essentially
step over the sharp peaks (if you double-click on the line graph and ask it
to mark the data points with symbols you can more easily see there are no
points where the peak should be).

I'm not sure I understand your point 1, but I think the intensity
variability may just be a consequence of the wavelength variability
discussed above. Normally one would try to adjust the lamp alignment using
radial scans, not wavelength scans, and typically the wavelength intensity
scans to check the strength of the 230 nm peak or wavelength calibration are
run at 6.5 cm.

John

-----Original Message-----
From: rasmb-bounces at rasmb.bbri.org [mailto:rasmb-bounces at rasmb.bbri.org] On
Behalf Of mitrana at mail.utexas.edu
Sent: Thursday, April 03, 2008 2:58 PM
To: 'RASMB'
Subject: [RASMB] Lamp Diagnostics

Hello Spinners
Our AUC started giving some problems recently. Did a wavelength scan and
here's a summary of the results -

1. Lamp intensity varies at the 5.9 cm position although at the 'sweet spot'
obtained from the lamp alignment this variation is about 9-10%.

2. Sometimes it seems the peaks are cut-off and I get a plateau instead of a
peak with of course a lower intensity count.

3. The peak oscillates 1-2 nm (227-230 nm and 526-528 nm) on successive
scans at a single radial position.

It seems like a monochromator problem to me but I'd like to hear some
comments from experts here. I am particularly worried about the peaks
getting cut-off.
Our facility did not renew the service contract this year (I know, extremely
bad idea but too many size exclusion column huggers around) and I'd rather
know the problem instead of being told by the Beckman Service person that
it's within specs while charging $290.00 per hour.

Mitra

--
Mitra S. Rana
Graduate Student
Institute for Cellular and Molecular Biology 2500 Speedway, UT-Austin
Austin, TX-78712 _______________________________________________
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