[RASMB] XL/I absorbance problem

[Borries Demeler]

Andrew, if your lamp is cleaned and you are only seeing 6k counts,
this suggests that something is blocking light in the light path.
Other sources of problems besides a dirty lamp could be:

lamp alignment
dirt in the slit assembly
oil film on the windows in the light path
dirt/obstruction on the monochromator

If all of this is OK, you may have a problem with the lamp.
Does the IF system also cause noisy scans?
if so, maybe your angle calibration is off and the lamp doesn't
fire until the septum or centerpiece wall is in the lightpath?

Just something else to check...

Good luck, -Borries


> 
> Hello all,
> 
> I'm not rally happy with the noise I'm seeing on my XL/I's
> absorbance scans, and I have a few queries. I'd be grateful for
> any comments.
> 
> 1. Noise seems excessive even on reasonable samples. Scans on
> an empty hole at 280 nm give an overall flat profile (in A280)
> but peak noise is +/-0.05. More peculiar is that the noise seems
> to be spikes, randomly distributed along radius and not in the
> same place on successive scans. (For comparison our old XL/A has
> peak to peak noise +/- 0.015 under the same conditions)
> 
> 2. Using the request data intensity option, the overall profile
> has a dip at r=6.3, but also numerous spikes, mostly upwards
> of about 600 counts on a background of 6000. Cleaning if anything
> has made this worse. (Cf about 3000 for the XL/A which does need
> cleaning.)
> 
> 3. A wavelength intensity profile looks normal though the maxima
> are not great (16000 at 230 nm after cleaning, 11000 before).
> 
> 4. What does the "request data incident" option in the GUI do?
> For the XL/A this produces very flat lines with some spikes upward
> or downward, of constant size; for the XL/A reasonably flat lines
> with random noise superimposed (4000 +/-100). As I don't know what
> this is measuring, I'm not sure what to expect.
> 
> I'll try and post some graphs later.
> 
> Many thanks,
> 
> Andrew
> 
> -- 
> Dr Andrew Leech                   *  Laboratory Manager
> Technology Facility               *  Molecular Interactions Laboratory
> Department of Biology (Area 15)   *  Tel   : +44 (0)1904 328723
> University of York                *  Fax   : +44 (0)1904 328804
> PO Box 373,  York  YO10 5YW       *  Email : apl3 at york.ac.uk
> _______________________________________________
> RASMB mailing list
> RASMB at rasmb.bbri.org
> http://rasmb.bbri.org/mailman/listinfo/rasmb
>