[RASMB] XLI absorbance problem

Tue Feb 24 11:21:59 PST 2015

Igor, I think the real 230 nm peak is much to the left of where your latest calibration graph starts. Compare to this slide showing intensity scans for clean and dirty lamps, and you will see there should be many more xenon emission peaks between 230 and ~500 nm. The error message is perhaps telling you that there really is a problem with the wavelength drive mechanism. 

You might try manually entering the wavelength calibration parameters from your other XL-I (after writing down the current ones so you can restore them) from the Service…Absorbance…Cal Parameters menu item and see if that gets you close enough that the normal calibration procedure will work.

John

From: Igor Perevyazko [mailto:i.perevyazko at gmail.com] 
Sent: Tuesday, February 24, 2015 9:40 AM
To: jphilo at mailway.com; Andrew Leech
Cc: RASMB List
Subject: Re: [RASMB] XLI absorbance problem

Dear All,

Once again, thank you very much for your comments and suggestions. 

We believe that we finally find out the origin of the problem: It seems that the wavelength calibration was completely out of range. We have made several wavelength calibrations assigning every time the 229 nm peak position to the very left point of the calibration curve. On the image attached you can see the new air-to air intensity spectra. We think that the very left peak should be related to the real 229 nm peak, however we cant do any further calibration process by the way mentioned above - diagnostic monitors appears with the following message: "DAB Wavelength out of range".  

Nevertheless, the wavelength scan of the KNO3 solution (c = 0.7 g/dl) gives us expected value of the optical density - 0.6 OD, but at the wrong wavelength - 272 nm (while it must be 302 nm). If you have any further suggestions regarding this problem please let me know. 

The low intensities in UV area obviously related with the problems of the lamp and/or absorbance optical scheme. 

Best regards

Igor 

On Tue, Feb 24, 2015 at 7:53 PM, John Philo <jphilo at mailway.com <mailto:jphilo at mailway.com> > wrote:

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 <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 <mailto:i.perevyazko at gmail.com> 
Cc: rasmb at list.rasmb.org <mailto: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 <mailto:rasmb-bounces at list.rasmb.org> ] on behalf of Curth
> [curth.ute at mh-hannover.de <mailto:curth.ute at mh-hannover.de> ]
> Sent: Tuesday, February 24, 2015 6:11 AM
> To: Andrew Leech
> Cc: rasmb at list.rasmb.org <mailto: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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