[RASMB] XLI absorbance problem

Tue Feb 24 09:39:33 PST 2015

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> 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] 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
> >
> > _______________________________________________
> > RASMB mailing list
> > RASMB at list.rasmb.org
> > http://list.rasmb.org/listinfo.cgi/rasmb-rasmb.org
> >
>
> --
> Dr Andrew Leech                   *  Laboratory Head
> Technology Facility               *  Molecular Interactions Laboratory
> Department of Biology (Area 15)   *  Tel   : +44 (0)1904 328723
> University of York                *  Fax   : +44 (0)1904 328804
> Wentworth Way,  York  YO10 5DD    *  Email : andrew.leech at york.ac.uk
> EMAIL DISCLAIMER: http://www.york.ac.uk/docs/disclaimer/email.htm
> _______________________________________________
> RASMB mailing list
> RASMB at list.rasmb.org
> http://list.rasmb.org/listinfo.cgi/rasmb-rasmb.org
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://list.rasmb.org/pipermail/rasmb-rasmb.org/attachments/20150224/075d57e9/attachment-0001.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 2015.02.24-WA(0.6 at 302nm).JPG
Type: image/jpeg
Size: 127905 bytes
Desc: not available
URL: <http://list.rasmb.org/pipermail/rasmb-rasmb.org/attachments/20150224/075d57e9/attachment-0002.jpeg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 2015.02.24-WA(Intensity).JPG
Type: image/jpeg
Size: 196739 bytes
Desc: not available
URL: <http://list.rasmb.org/pipermail/rasmb-rasmb.org/attachments/20150224/075d57e9/attachment-0003.jpeg>