[RASMB] XLI absorbance problem

[John Philo]

Well actually I have to disagree that Igor's counterbalance scan is fine,
because I think it proves that the radial calibration is incorrect. The
outer edge should be at 7.15 cm, but it appears to be at ~7.10 instead.
However I don't think that can explain the main problem we have been
discussing. 

The fact that the radial scan Igor sent on Saturday shows two meniscus peaks
I think disproves the hypothesis that the instrument is scanning the
reference channel twice (no data from the sample channel). I had been
thinking that perhaps the lamp pulse was somehow lasting so long that light
was going through both channels with each pulse, but I think this scan also
throws out that idea.

I agree that most of Igor's observations suggest that the wavelength is far
off or even that essentially white light is coming through. However the
radial intensity scans Igor sent early on seem to show that the wavelength
selection is working (but again the intensities are too similar for sample
and reference). The radial scan data show the expected sharp meniscus peaks,
which seems to rule out a major malfunction with the slit assembly. Overall
I can't come up with any hypothesis consistent with all the data Igor has
given us. 

What does seem clear to me is that even the collected wisdom of this group
can't come up with any quick fix, or one that won't require messing with
parts not normally serviced by end-users, and thus it appears this problem
will require a Beckman service call to resolve. The best test to convince
Beckman that the instrument is out of spec is to scan one of the Beckman
absorbance standard solutions.

John

-----Original Message-----
From: RASMB [mailto:rasmb-bounces at list.rasmb.org] On Behalf Of Andrew Leech
Sent: Tuesday, February 24, 2015 5:57 AM
To: i.perevyazko at gmail.com
Cc: rasmb at list.rasmb.org
Subject: Re: [RASMB] XLI absorbance problem

Hi all,

Perhaps there could be a problem with the wavelength drive in the affected
XL/I - if the drive rod is not working properly this would account for the
fact that the monochromator was ok in the other machine. Tom's suggestion
should show this up.

Best regards,

Andrew


On 24/02/2015 13:46, Laue, Thomas wrote:
> Hi-
> I suggest you take a wavelength scan on an empty hole and send along those
results. The original intensity scans showed there was no (or very little)
difference in intensity between the sample and reference sectors. This would
be true if the wavelength were being reported incorrectly. The counterweight
scan looks fine (though I agree that the intensity seems low), you can see
the slight difference in the size of the holes. This would indicate that the
timing and radial position calibration are OK.
> Best wishes,
> Tom
> ________________________________________
> From: RASMB [rasmb-bounces at list.rasmb.org] on behalf of Curth 
> [curth.ute at mh-hannover.de]
> Sent: Tuesday, February 24, 2015 6:11 AM
> To: Andrew Leech
> Cc: rasmb at list.rasmb.org
> Subject: Re: [RASMB] XLI absorbance problem
>
> Hi Andrew,
>
> if I do an intensity scan of the counterbalance with our XL-I in 
> continuous mode, I get similar intensities. In step mode, however, the 
> intensities are much higher. So, if it was performed in continuous 
> mode, the scan of the counterbalance looks fine to me.
>
> Best wishes,
>
> Ute
>
> --
>> Prof. Dr. Ute Curth
>> Hannover Medical School
>> Research Core Unit for Structural Analysis, OE 8830 Carl-Neuberg-Str. 
>> 1
>> 30625 Hannover
>> Germany
>
>> Tel.:+49-511-5329372
>> Fax :+49-511-5325966
>
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-- 
Dr Andrew Leech                   *  Laboratory Head
Technology Facility               *  Molecular Interactions Laboratory
Department of Biology (Area 15)   *  Tel   : +44 (0)1904 328723
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