[RASMB] Lamp Diagnostics

mitrana at mail.utexas.edu mitrana at mail.utexas.edu
Thu Apr 3 18:00:13 PDT 2008


John
I feel better already.

What I meant in 1. is that I take a wavelength scan at 5.9, 6.5, and 7.1 cm and
compare the 230 nm peaks. I guess a radial scan is definitely a better way to
check intensity variability across a cell. How much variability is considered
acceptable - somehow 10% seems stuck in my head.

Mitra

Quoting John Philo <jphilo at mailway.com>:

> 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 _______________________________________________
> RASMB mailing list
> RASMB at rasmb.bbri.org
> http://rasmb.bbri.org/mailman/listinfo/rasmb
>


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



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