[RASMB] XL/I absorbance problem

Virgil Schirf schirfv at biochem.uthscsa.edu
Wed Jun 13 07:22:29 PDT 2007


Andrew,

We've seen this type of occurrence. The problem may lie in your slit 
assembly where the movement is not smooth and spikes occur. The 
wavelength scan is at a stationary position and you won't see any 
problems, but they show when the slit is moving. One way to diagnose 
this type of problem is to check the menisci of the sample and reference 
and see if they "jump" around randomly resulting in broad menisci that 
look as if there is a small vacuum leak. The slit assembly motor may 
have have a problem, the edges of the PMT cover may have gotten 
scratched, dirt has built up on the rails of the slit assembly, or they 
may be a problem in the circuitry of the heat sink, although that is rare.

Cheers,

Virgil

Leech, AP wrote:
> 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
>


-- 

Virgil Schirf
Manager, CAUMA <http://cauma.uthscsa.edu> & CLS <http://cls.uthscsa.edu>
Department of Biochemistry, Rm 4.523U
The University of Texas Health Science Center
7703 Floyd Curl Dr.
San Antonio TX 78229-3900
Voice mail: 210 567-6590
Fax: 210 567-6595
Email: schirfv at biochem.uthscsa.edu <mailto:schirfv at biochem.uthscsa.edu>



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