[RASMB] question for XLA experts

[Jo Butler]

If I may follow up this side point raised by Kristian, I have also tried 
using transmission scans rather than absorbance, though in my case it was 
with the desire to get closer to the direct measurements for fitting of 
equilibrium data.  However the major problem which I found was that the 
firmware would not allow one to take multiple readings at each datum point 
and to get the mean and s.d. of the value.  Repeat scans were not much 
help, as the radial accuracy was insufficient.
Thus, I think that Kristian's suggestion is fine if one only wants a single 
reading at each point, but falls down when one wants averaging to improve 
the signal to noise of the data.

Jo

--On Thursday, November 15, 2001 11:11 pm +0100 Kristian Schilling 
<schilling at nanolytics.de> wrote:

>
> As a matter of fact, we have turned to acquire all scans in the intensity
> mode in order to recognize any errors in the raw data that might look
> like absorbance signals later. We then transform the data into Abs units
> after import into evaluation software. This has proved extremely helpful
> especially with density gradients.
>
> Hope this helps,
>
> Kristian
>
>
>
> At 15:08 15.11.01 -0600, you wrote:
>> Hi,
>> I am trying to calibrate our rotors for speed-dependent rotor stretching
>> and the channel positions of our centerpieces. The problem I am facing is
>> that it seems to be very difficult to assign the exact bottom of a
>> channel to a peak from an absorption scan.
>>
>> Attached is a typical absorbance scan of an empty 6-channel centerpiece.
>> For the first channel, I labeled the peaks 1-10 and found the radial
>> positions for them, shown below:
>>
>> 1 = 5.741
>> 2 = 5.768
>> 3 = 5.790
>> 4 = 6.125
>> 5 = 6.138
>> 6 = 6.186
>> 7 = 6.234
>> 8 = 6.249
>> 9 = 6.273
>> 10 = 6.286
>>
>> I then scanned the centerpiece on a 3200 DPI scanner and came up with
>> these dimensions (believe it or not, a half-way decent scanner does a
>> pretty good job at measuring small parts, good to within +/- 0.01 mm!)
>>
>> Cell dimensions:
>>
>> first channel: 3.83 mm, darkspace: 1.27 mm (channel width: 3.29 mm)
>>
>> Now can someone tell me which peaks correspond to the channel bottom?
>> Or won't I be able to find it correctly with absorbance optics, should
>> I use interference optics? I guess IF has a better radial resolution,
>> is it also as accurate as the absorbance radii?
>>
>> Any suggestions would be appreciated.
>>
>> -Borries
>
>
>
> =================================
> Nanolytics
> Gesellschaft fuer Kolloidanalytik mbH
> Dr.  Kristian Schilling
>
> Hauptstr. 20
> D-14624 Dallgow
>
> Tel.:		+49/3322/24200-5
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> e-mail:	schilling at nanolytics.de
> Internet:	www.nanolytics.de
>
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P.J.G. Butler,
MRC Laboratory of Molecular Biology,
Hills Road, Cambridge, CB2 2QH, UK.
Tel. +44 (0)1223 402296