[RASMB] XLI absorbance problem

[John Philo]

Igor, that empty cell scan looks good to me. Could you send us a radial intensity scan of a cell containing something with an OD in the range of 0.5 to 1? Also are you using an 8-hole or 4-hole rotor?

 

John

 

From: RASMB [mailto:rasmb-bounces at list.rasmb.org] On Behalf Of Igor Perevyazko
Sent: Friday, February 20, 2015 8:05 AM
To: Borries Demeler; andrew.leech at york.ac.uk
Cc: RASMB List
Subject: Re: [RASMB] XLI absorbance problem

 

Dear Andrew, dear Boris

Thank you very much for your suggestions! 

Well, the interference optics works fine on the same cell and as can be seen by eye the magnetic dot on the stripped ring seems to be ok. At the moment I have only tried the same cell and monochromator on the working XLI

Regarding the Borris's points:

I have performed the intensity scan with an empty cell in the hole and the radial position is in the normal range (left on 5.8 and right on 7.15), so the radial calibration seems to be ok. The thing is that as you can see on graph 2, I have also checked the intensity of  reference (benzene) and the sample sector filled with dye solution (Pyrene) and it has practically the same intensity level as if I scan an empty cell.  As I see it, if there was a delay problem the intensity of a cell filled with a solution must be close to 0 then, if I understand your concern correctly. I have also attached the radial intensity scan for a cell (no windows).

 

Best regards

Igor

 

On Fri, Feb 20, 2015 at 6:31 PM, Borries Demeler <demeler at biochem.uthscsa.edu <mailto:demeler at biochem.uthscsa.edu> > wrote:

Dear Igor,
I agree with Andrew, this looks like a timing problem, obviously when
you intensity scan an empty hole it doesn't have this problem (no septum,
cell components in the light path) so the timing being a little bit off
still lets it hit the hole, just not a 2.5 degree channel. Can you still
perform an intensity scan when you put an empty cell in the hole? I am
not sure what the radial position was. If the radial calibration is off
you may not be at the position you think you are, so radially scan an empty
cell or the counterbalance and make sure the edges are at reasonable positions.

-b.

On Fri, Feb 20, 2015 at 04:20:53PM +0300, Igor Perevyazko wrote:
> Dear RASMB members,
>
>
>
> We are having a problem with absorbance optics on XLI centrifuge(XLI_1 on
> the images attached). Hopefully you can suggest something that will
> help. The problem is that optical density of any samples (which definitely
> absorb, including for example BSA (c = 4mg/mL) or pyrene dye (c = 10然 ))
> recorded by the AUC is within the zero  level. Nevertheless, at much higher
> concentrations (approximately 10 -20 times higher) the optical density
> reaches some level of absorbance (~0.1-0.2 OD). The same solutions checked
> by normal UV-Vis spectrophotometer and on another XLI centrifuge (XLI_2),
> have adequate values of the absorbance level. We have as well checked our
> monochromator   on  XLI_2 and it was working ok. Recorded lamp intensities
> (air to air) at 230 nm and 530 nm are at the normal level. If we perform
> the absorbance scan of a sample (for example Pyrene dye at c = 10然)  in
> the intensity mode, we received the same level of intensities for both
> reference and sample chamber! The corresponding comparison of the
> intensities is shown on the image attached. Any of your suggestions about
> the possible problem and/or the solution will be highly appreciated.
>
>
> Best regards
>
> Igor Perevyazko
>
>
> PhD Igor Perevyazko
> Physics Department, Polymer Physics
> St.Petersburg State University
> Ul. Ulyanovskaya 1, Petrodvorets
> St.Petersburg, Russia, 198504
> Tel.: (812)4284382
> Fax.: (812)4287240



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